EXTERNAL STUDIES PROGRAMME ABN 200 Introduction to Agricultural Biochemistry Vmvemty of Ibadan, Ibadan. UNIVERSITY OF IBADAN LIBRARY ABN 200 Introduction to Agricultural Biochemistry UNIVERSITY OF IBADAN LIBRARY IBADAN EXTERNAL STUDIES PROGRAMME SERIES ABN 200 INTRODUCTION TO AGRICULTURAL BIOCHEMISTRY by Dr. O. J. Babayemi Dr. O.A. Abu Mr. O.A. Sokunbi Department o fA nimhl Science, University o f Ibadan r m r i Published by InÄ fa The Centrefor External Studies University of Ibadan UNIVERSITY OF IBADAN LIBRARY © Centre for Extemal Studies University o f Ibadan Ibadan All rights reserved. No part of this publication may be reproduced, stored in a rctrieval System, or transmitted in any form or by any means, electric, mechanical, photocopying, recording or otherwisc, without thè prior permission of thè copyright owner. First published 2002 ISBN 978-021-075-x V Series Editor: C.O. Adejuwon Printed by Ibadan University Printery (A Division o f U.I. Ventures Limited, Ibadan) UNIVERSITY OF IBADAN LIBRARY Contents Vice Chancellor’s Message vii Foreword ix General Introduction and Course Objectives xi Lecture One: General Introduction 1 Lecture Two: Amino Acids 5 Lecture Three: Structure, Properties and Classification of Proteins 11 Lecture Four: Non-Protein NitrogenoUs Compound 19 Lecture Five: The Chemistry of Carbóhydrates I 22 Lecture Six: The Chemistry of Carbóhydrates II 27 Lecture Seven: The Chemistry of Lipids 39 Lecture Eight: Introduction to Minerals in Animai Nutrition 47 Lecture Nine: Macro-and Micro-Minerals in Animai Nutrition 51 Lecture Ten: The Vitamins 58 Lecture Eleven: The Nature, Properties and Classification of Enzymes 69 Lecture Twelve: Enzymes, It’s Mode of Action and Inhibition 73 Lecture Thirteen: The Nature, Classification and Functions ofHormones 79 Lecture Fourteen: Organisation and Control of Endocrine Systems. 85 / UNIVERSITY OF IBADAN LIBRARY LECTUREONE / General Introduction Introduction The Agricultural Biochemistry and Nutrition (ABN 200) titled introduction to Agricultural Biochemistry is an introductory to fundamental nutrients in food. Nutrients are group of food constituents of thè same generai Chemical composition that aids in thè support of life. These unavoidable substances are essential for thè preservation of life. The basic nutrients to be discussed in this course are proteins. carbohydrates, lipids, minerals and vitamins. Ànother important substance although not nutrient, but assist in proper functioning of nutrients are hormones and enzymes. Feed nutrients are vital for animals by performing thè following functions ( 1 ) provision of essential elements for repairing thè deteriorating cells (2) provision of raw materials for synthesis of body tissues in growth (3) serving as a source of energy for vital processes in thè body, growth, work or production (4) for generating heat necessary for maintaining body temperature (5) raw material for thè production of milk, meat, egg or wool as thè case may be. Objectives At thè end of this lecture, students will be able to identify thè basic nutrients required for thè upkeep of fami animals and be able to differentiate their fundamental roles. Pre-Test 1. List thè necessary nutrients that are indispensable to farm animals. 2. Explain thè occurrence of protein, carbohydrates, lipids, minerals, vitamins, hormones and enzymes in nature. 1 UNIVERSITY OF IBADAN LIBRARY CONTENT This lecture wiTI discuss what, why, when and how of proteins, carbohydrates, lipids, minerals, vitamins, hormones and enzymes. Proteins The major component of soft tissues and internai organs, e.g. liver, kidney, heart, lungs, etc o f animai body is protein. For growth and repair to be sustained in animai, there mustbe transformation of food protein into body protein. Proteins are complex compounds, each molecule being composed of a considerable number of amino acids. The animals build their body proteins primarily from thè amino acids absorbed from thè digested dietary proteins. The only consideration for thè absorption of protein is when it has broken down into amino acids. The terms essential and non-essential amino acids means that thè essential amino acids have to be supplied from extemal sources. The nori-essential amino acids missing in thè diet can be produced in thè body from other sources. In thè preceding lectures of this course, we shall somehow look into thè structures and properties of amino acids and protein. The lecture will also consider some nitrogenous compounds that are not true protein, but found in plants and animals. Carbohydrates The principal part of food for animals is carbohydrates. However, it is suffice to say that none of thè carbohydrates is found as such in thè animai body, thè only exceptions being glycogen and small amount of sugar. The term carbohydrate connotes thè presence of carbon, hydrogen and oxygen, thè latter two in thè proportion as seen in water. These compounds are very important in nutrition of animals because they are thè chief source of energy for thè animals for maintenance, growth, production and work. They also hèlp thè animals to maintain their body temperature. Carbohydrates include sugars, starch, cellulose, hemicellulose, pectins, gums, and mucilages. Sugars are thè simplest carbohydrates which are sweet and soluble in water. Starch, a polymer of glucose is a major component of animals’ diet. Plants store excess food nutrients as starch, as a reserve. Starch is not soluble in Water but easily broken down to sugars in a process of digestion. Cellulose is a more complex and less soluble and digestible carbohydrate. Thus, cellulose has a very limited role as a nutrient in thè case of camivorous and omnivorous animals. This lecture will bring to a deem light thè chemistry of carbohydrates which will involve simple and complex structures. 2 UNIVERSITY OF IBADAN LIBRARY Lipids Lipids are biological substances that are soluble in organic solvents. Apart from being structural components of biological membrane, they also play a major role in thè nutrition of thè animai. Just as carbohydrates can be a supply of energy, lipids can also fulfil this function in a higher way. Later, we shall focus on functions of lipids and structures of some common ones. Minerals Minerals are significant for normal activities in farm animals. About 40 minerals have been discovered to occur naturally in thè tissues of animals and plants. Out of these 40, thè dietary essential minerals are those that have been shown by research to have essential metabolic roles in thè body. The 27 basic dietary essential minerals include Ca, P, Mg, Na, K, Cl, S, Mn, Fe, Cu, 1, Zn, F, Vn, Co, Mo, Se, Ni, Cr, Si and Sn. Part of thè study on minerals shall include trace and major minerals, fundamental roles of minerals, requirements for different animals and their deficiencies. Vitamins Vitamins are conveniently classified into water and fat soluble vitamins. Vitamins are part of a complete diet although needed in only minute amounts but essential for animai production. Vitamins are very essential in that they cannot be produced by animals tissues at all or in sufficient quantities to supply thè needs under normal circumstances. Hormones and Enzymes Hormones are organic compounds produced in one part of thc body and then transported to other parts of thè same body where they produce a response. Enzymes are molecules which catalyse biochemical reactions by acting on their substrates and converting them into products. In our subsequent lectures, we shall be detailed about thè action, mode and thè targets of hormones and enzymes. Summary The first lecture introduced you to thè basic nutrients, their structures, properties and functions. It is however, a periphery of thè expected. The nutrients that have been highlighted are proteins, carbohydrates and lipids, minerals and vitamins. Hormones and enzymes are not nutrients but essential for thè metabolism of thè nutrients afore mentioned. 3 UNIVERSITY OF IBADAN LIBRARY Post-Test 1. List thè basic nutrients that are required by fami animals. 2. What are thè end products of proteins and carbohydrates? 3. State thè functions of protein and carbohydrates. Reference Maynard* L.A. , Looshi, J.K., Hintz, H.F. and Warner, R.S. (1983). Animai Nutrition. 7h Edition. Publishedby Tata McGrar Hill Publishing Company Limited. 4 UNIVERSITY OF IBADAN LIBRARY LECTURE TWO Amiùo Acids Introduction Protein is an indispensable nutrient required by animals for growth, replacement of deteriorating cells and generally for body health. Protein is important, but one of thè essential nutrients required to uphold thè body’s health. Chemically, proteins are complex organic compounds that contain thè same atoms as carbohydrates and lipids. The constituents are carbon, hydrogen and oxygen. However, protein, in addition to these compositions also contains nitrogen and sulphur. In this lecture, you shall be taken through thè amino acids which are thè smallest particles obtained when complex protein is broken down by thè process of digestion. Objectives At thè end of this lecture, students will be able to catch thè glimpse of amino acids in terms of structure, properties and indispensabilities. Pre-Test 1. What are amino acids? 2. From thè structure of amino acid, list three constituents that make thè structure. 3. Mention nine essential amino acids. 4. State properties of amino acids. CONTENT Meaning and structure of amino acids. Essential amino acids and properties of amino acids will be discussed step by step as follows: Meaning and Structure of Amino Acids The end product of a systematically hydrolysed proteins by digestive enzymes, acids or alkalis is known as amino acids. There are well over 200 identified amino acids, out of which 20 frequently occur as components of proteins. There is no amino acid that does not have identical fundamental structure. 5 UNIVERSITY OF IBADAN LIBRARY The structure is a carbon (C) with three groups of atoms attached to it: 1) an amino group (NH2) 2) an acid group (COOH) and 3) a hydrogen atom (H) Essentially, carbon atoms need to possess four bonds but thè differences between one amino acid to thè other is thè fourth attachment. Side group 0 II H - N - C - C - O - H Amino | | Acid group group H Hydrogen > atom Amino acid structure Common Amino Acids As mentioned at thè beginning of this lecture, there are 20 common amino acids that proteins are made up of. In order to understand it better, thè amino acids are classified into: 1. Monoamino-monocarboxylic acids. These include: H I (a) Glycine NH, - C - COOH (b) Alanine CH3 I H NH, C - COOH I H c h3 CH3 c h 3 c h 3 \ / \ / CH CH (c) Valine I (d) Leucine I NH2 - C - COOH CH, I H NH2 - C - COOH I H 6 UNIVERSITY OF IBADAN LIBRARY 2 CH,ch oh I I H - C - OH (e) Serine n j_[ C COOH (0 Threonine I I NH, C - COOH H I H CH, \ CH, CH, (g) Isoleucine \ / CH NH, C COOH I H 2. Sulphur-containing amino acids. Examples are: CH, I S CH,SH I I CH, (i) Cysteine NH, - C - COOH (ii) Methionine I ' I H CH, I NH, - C - COOH I H 3. Monoamino-dicarboxylic acids COOH CO-NH, I I CH, CH, (i) Aspartic acid | (ii) Asparagine I NH, - C - COOH NH,-C-COOH ' I ' I H H 7 UNIVERSITY OF IBADAN LIBRARY COOH c o - n h 2 I I CH, CHj I ' (iii) Glutamic acid CH, (iv) Glutamine c jj I I 2 NH, - C - COOH NH2-C -C O O H ‘ I I H H 4. Basic amino acids. They are as follows: NH2 CH,NH2 I ì 2 C = NHc h I CH, NH (i) Lysine I (ii) Arginine | CH, (CH2)3 I NH - C - COOH I I NH, - C - COOH H ' I H H C - N ^ CH I / C -N H (iii) Histidine L„ NH, - C - COOH I H 8 UNIVERSITY OF IBADAN LIBRARY 5. Aromatic and heterocyclic — These include: x x OH 1 a) Phenylalanine b) Tyrosine L J CH, | ' i NH.-C-COOH NH22 - Ci - COOH 1 H H H ^ CH\ 1 HC C - C - CH2- C - COOH Tryptophan 1 HC C CH n h 2 \ c h / V NH f i 2 - d) Proline : h C - C O O I ^N H/ Iù Essential Amino Acids The animai’s body is capable of inducing more than $0% of thè aforementioned amino acids for itself. However, there are basic nine amino acids that possibly cannot be synthesized or produced in sufficient amount to meet thè réquirement. These nine amino acids must be supplied by thè diet. They are therefore essential amino acids. The nine essential amino acids are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Properties of Amino Acids 1. Amino acids are amphoteric which exhibits dual properties of both basic and acidic 9 UNIVERSITY OF IBADAN LIBRARY 2. In acqueous solution, amino acids exist as dipolar ions. 3. In alkaline and strong acid Solutions, amino acids exist as an anion and a cation respectively. 4. Amino acids possess isoelectric point which is a pH value for a given amino acid at which ìt is electrically neutral. 5. Amino acids act as buffers, resisting changes in pH. 6. None but all thè amino acids involved in protein structure have an L- configuration. Summary Proteins are complex organic compounds that contam C,H,0,N and S. when protein undergo digestion through thè action of enzymes, it is broken down to a simpler food substances called amino acids. In nature, more than 200 amino acids exist but only 10% of these occur as component of proteins and are known as common amino acid. Structurally it has a carbon upon which three groups of atoms are anchored. There are essential amino acids that cannot be produced by thè body itself but have to be supplied through thè diet. Amino acids generally possess certain properties which are amphoteric, dipolar ions, isoelectric, buffers and L-configuration._________________________________________________ Post-Test 1. a) What are amino acids? b) List thè three groups of atoms that are attached to carbon form structure for amino acids. 2. Classify amino acids into five and structurally give 2 examples each. 3. List essential amino acids, state why they are vital than others. 4. Enumerate properties of amino acids. References Dickerson, R.E. and I. Geis (1983). Proteins: Structures, Function and Evolution. Benjamin (Cummings. Menlo Park, Calif). Lehninger, A.L. (1982). Principles o f Biochemistry.New York: Worth Pubi. Linder, M.C. (1991). Nutritional Biochemistry and Metabolism.New York: Elsevier. McDonald, P., R.A. Edwards, J.F.D. Greenhalgh (1987). Animai Nutrition. Fourth edition. ELBS, London. Whitney, E.N. and S.R. Rolfes (1993). Under standing Nutrition. New York: West Pubi. Comp. Los Angeles. 10 UNIVERSITY OF IBADAN LIBRARY LECTURETHREE Structure, Properties and Classification of Proteins » Introduction In our last lecture, we endeavoured to consider thè smallest particles of protein called amino acids. We also studied thè structure, properties and classification of amino acids. In this chapter, we will proceed to appraise protein in its entirety. It is essential to discuss its framework, its characteristics and various classes. Objectives By thè end of this class, students will be able to itemize structures of protein, properties of protein and thè major classification of protein. Pre-Test 1. List four structures of protein and discuss their peculiarities. 2. State various properties of protein. 3. Briefly classify proteins and give at least 2 examples of each. CONTENT This chapter will highlight thè structure of proteins (primary, secondary, tertiary and quatemary), properties of proteins and classification of proteins (simple, conjugated and derived). Structure of Protein Protein, as a substance has different frameworks. For your proper understanding, we shall present that structure of proteins under primary, secondary, tertiary and quatemary proteins. i) Primary Structure: This structure comes to existence as a consequence of thè linkage between thè a - Carboxyl of one amino acid and thè a - amino group of another acid. 11 UNIVERSITY OF IBADAN LIBRARY This type of linkage is known as peptide lmkage and it is a linkage formed between two amino acids followed by. thè elimination of water as revealed in above structures. In thè illustrated structure, a dipeptide was formed from two amino acids. Numerous amino acids can be married together using this addition procedure. When this happened with thè removai of one molecule of H ,0 at every linkage, thè polypeptides are produced. H R 0 Linkage H R 0 Linkage H R 0 I I II \ I I II N I I II H - N - C - C -(QH + H )~ N - C - C -(OH + H j - N - C - C - O H H H 1 1 H R O H R O H R O I I II I I II I I II H - N - C - C - N - C - C - N - C - C - O H + 2H,0 I I I H H H Polypeptide ii) Secondary Structure — This structure shows thè conformation of thè chain of amino acids emanating due to production of hydrogen bonds between thè imido (NH) and carboxyl groups of adjacent amino acids as illustrated below: 12 UNIVERSITY OF IBADAN LIBRARY H R H H o I / N v y j i ) N II / \ r i o h r H R ,H o H R H v - N V " V V c\ N ^ '/ N / Ò H IH R O H iii) Tertiary Structure — This structure is formed as a result of further interraction of secondary structure through thè R groups of thè amino acid residues. Such emanated interraction predisposes polypeptide chain to folding and bending. iv) Quaternary Structure — Proteins have this structure if they contain more than one polypeptide chain. The agents that equilibrate these combinations are hydrogen bonds and salt bonds produced between residues on thè surfaces of polypeptide chains. Properties of Proteins 1. Colloidal — Proteins are peculiar in their water solubility. Keratin and albumins are insoluble and soluble proteins respectively. Soluble proteins can be precipitated from solution and such precipitation can in tum be redissolved. 2. Amphoteric — All proteins possess a certain amount of free amino and carboxyl groups, either as terminal units or in thè side-chain of amino acid residues. 3. Denaturation — All proteins can be altered or dephased from their naturai occurrence. It is a Chemical, physical and biological alteration of a unique 13 UNIVERSITY OF IBADAN LIBRARY structure ofproteins. Coagulation of a protein solution upon heating, shrinking of meat when heated or fried and roasting of nuts are few examples of denaturation of protein. Classification of Proteins Proteins can conveniently be grouped on thè basis of both physical (shape) and Chemical properties. The physical properties commonly employed for grouping are those of solubility and heat coagulation. Standing on these two characteristics; proteins are classified into three as simple, conjugated and derived proteins. A. Simple Proteins Simple proteins are thè proteins that yield only amino acids or their derivatives when hydrolysed. Examples are many which include albumins, globulins, glutelins, albminoids, histones, prolamins. It is impoftant we briefly examine these simple proteins. i) Albumins — Soluble in water and coagulable by heat. They are found both in plants and animais, e.g. myosin of muscle, serum albumin of blood and lactalbumin of wheat. ii) Globulins — These are not soluble in pure water but could be dissolved in solution of alkaline and acid. They are heat coagulated. They generally contain glycine. Globulin constitute an important and widely distributed group of animai and plant proteins. For example, ovoglobulin of egg yolk, myosin of muscle, phaseolin of beans, legumins of peas and arachin of peanuts. iii) Glutelins — Are all plant proteins and soluble in very dilute acids and alkalis but they are insoluble in naturai solvents. iv) Prolamins— Prolamins are soluble in alcohol but insoluble in water or neutral solvents. These proteins generally yield proline and amide nitrogen upon hydrolysis but are deficient in lysine. Prolamins are plant proteins found principally in seeds, e.g. zein of com, hadein of barley, gleaden of wheat. v) Albuminoids — It is thè least soluble of all thè proteins. They are generally insoluble in water, dilute acids, alkalis and alcohol. They are entirely animai protein and are thè chief constituents of skeletal structures such as hair, hom, hoof, and nails. They are also constituents of supporting and connecting of fibrous tissues and of thè cartilage and bone. 14 UNIVERSITY OF IBADAN LIBRARY vi) Histones — The proteins are soluble in water and insoluble in dilute ammonia They are readily soluble in dilute acids and alkali. They are not readily coagulated by heat. Histones are basic proteins. They yield a large proportion of basic amino acids upon hydrolysis. They often precipitate other proteins from solution. vii) Protamins — Protamins are strongly basics and yield mainly basic amino acids on hydrolysis particularly arginine. They are soluble in water, dilute ammonia acid and alkalis. They are not coagulated by heat. They precipitates other proteins from their solution. B. Conjugated Proteins Conjugated proteins are composed of simple proteins combined with non-proteins substance. The non-protein group is referred to as prosthetic group or addition group. The types of conjugated proteins include thè following: 1) Nucleo proteins — They composed of simple basic protein (protamin or histone) in salt with nucleo acid or nucleic. They are proteins of celi and apparently thè chief constituents of chromatin. These are thè most abundant in tissues of both plants and animals, having a large proportion of nucleic materials such as yeast, thymus and other glandular organs. 2) Mucoproteins or mucoids — The mucoproteins are composed of simple proteins combined with mucopolysaccharide such as hyaluromc acid, chomdrotin sulphates. They generally contain large amount of N-acetylated henosamine and in addition + or - of such substances are uronic acid, sialic acid and monosaccarid. Water soluble mucoprotein have been obtained from human urine, serum and egg white. Each water soluble mucoprotein are not easily denatured by heat or readily precipitated by agents such as picric acid and trichloro acetic acid. 3) Chromoproteins — These proteins are composed of simple proteins united with coloured prosthetic group. Many proteins of important biological function belongs to this group. Examples of chromoproteins are: a) Haemoglobin:- Respiratory proteins in which thè prosthetic group is iron containing prophysm called EME. b) Cytochromes:- These are cellular of oxidation, reduction protein in which thè prosthetic group is also HEME. 15 UNIVERSITY OF IBADAN LIBRARY c) Flavoproteins:-. They are cellular oxidation-reduction proteins in which thè prosthetic group are riboflavin. d) Visual purple of thè retina:- It is a chromoprotein in which thè prosthetic group is carotenoid pigment. 4) Phosphoproteins — Phosphoric acid is thè prosthetic group of phospho- protein. Phosphosenine has been isolated from casein (milk) and vitellin (egg). 5) Lipoproteins — Lipoproteins are formed by combination of proteins with lipid such as lecithin, cephalin, fatty acid, etc.' phospholipid proteins are widely distributed in plants and ammals, milk, and in chloroplast of plant. 6) Metalloproteins — This is a large group of enzyme proteins which contain metallic element such as Fe, Co, Mn, Zn, Cu, Mg, etc. which are parts of their essential structures. C. Derived Protein This class of proteins as thè name implies mcludes those substances formed from simple and conjugated proteins. It is thè least well defined of thè protein group. Derived proteins are sub-divided into primary and secondary. Primary Derived Protein This protein derivatives are formed by processes which cause only slight changes in thè protein molecules and its properties. There is little or no hydrolytic cleavage of peptide bond. The primary derived proteins are synonymous with denatured protein. Examples of primary derived proteins are: 1 ) Proteans — They are insoluble product formed by thè incipient action of H20, very dilute acids and enzymes. They are particularly formed from certain globulins and differ from globulins being insoluble in dilute salt solution. 2) Metaproteins — They are formed by thè actiort of acids and alkalis upon protein. They are generally soluble in very dilute acid and alkalis but insoluble in neutral solvent. 3) Coagulatedproteins — These are thè soluble proteins formed by thè action of heat or alcohol upon naturai protein. 16 UNIVERSITY OF IBADAN LIBRARY Secondary Derived Protein The substances are produced in thè continuous hydrolytic cleavage of thè peptide unions of protein molecules. They represent a great complexity of protein molecules of different sizes and amino acid composition. They are grouped into proteoses, peptones, peptides according to average molecular complexity. Each group is composed of many substances. 1 ) Proteoses — These are hydrolytic product of proteins which are soluble in water and not coagulated by heat and are precipitated from their solution by saturation with (NH4), S04. 2) Peptones — Peptones are hydrolysed in water. They are not coagulated by heat and not precipitated by saturation with (NH4)2 S 04. 3) Peptide — They are composed of only a relatively few amino acid united through peptide bonds. They are named according to thè number of amino acid group present as di, tri, tetra, penta, — peptide, etc. They are water soluble, not coagulated by heat, not salted out of solution and are often precipitated by phosphotungstic acid. Summary Protein possesses different structures in which it can be identified. There are four basic structures that include primary, secondary, tertiary and quatemary proteins. Proteins are endowed with distinctive characteristics which ranges from colloidal, amphoteric and denaturation. For conveniences, proteins are classified into simple proteins (albumins, globulins, glutelins, prolamins, albuminoids, histones, and protamins), conjugated proteins (nucleo proteins, mucoproteins, chromoproteins, phosphoproteins, lipoproteins, metalloproteins) and derived proteins (primary and secondary derived proteins). Post-Test 1. Enumerate structures of proteins. 2. Identify thè inherent characteristics of proteins. 3. Discuss thè following with specific examples: a) Simple proteins b) Conjugated proteins c) Derived proteins 17 UNIVERSITY OF IBADAN LIBRARY References Linder, M.C. (1991). Nutritional Biochemistry and Metabolism. Elsevier. McDonald, P., R.A. Edwards and J.F.D. Greenhalgh (1987). Animai Nutrition. 4* ed. ELBS. 18 UNIVERSITY OF IBADAN LIBRARY LECTURE FOUR Non-Protein Nitrogenous Compound Introduction There are true proteins as earlier discusseci. These are thè proteins that are routinely analysed for in Chemical analysis. However, there are some nitrogenous compounds that are not true protein, but found in plants and animals. They are classified as non-protein nitrogenous (NPN) compounds. Certain amino acids such as, alanine, glutamic acid, serine, aspartic acid, glycirte and proline belong to NPN. Some other NPN compounds are lipids, amines, amides, purines, pyrimidines, nitrates and alkaloids. Also, numerous vitamin B complex possess nitrogen in their structure, e.g. thiamine, riboflavin, Niacin, pantothenic acid, Vitamin B6, etc. Objectives At thè end of this chapter, students will be able to differentiate thè difference between true protein and non-protein nitrogen. Pre-Test 1. State examples of true protein 2. Define non-protein nitrogenous compounds. 3. List various examples of NPN compounds and where they are obtained. CONTENT Our discussion in this lecture today will revolve around specific and common NPN compounds to include (1) Amines, (2) Amides, (3) Nitrates, (4) Alkaloids and nucleic acids. Amines Amines occur in nature as fundamental compounds that are available in various animai and plant tissues. In decayed or decaying organic matter, sizeable number of amines occur as toxic decomposition products. Through thè process of decarboxylation of amino acids, many of thè micro-organisms are capable of 19 UNIVERSITY OF IBADAN LIBRARY yielding amines. Under certain circumstances, these may be produced in thè rumen o f any ruminants that could culminate in physiological symptoms. In a poorly prepared silages for pasture preservation, which clostridia predominated thè fermentation, significant amount of amines are contained. Betaine is a tertiary amine whose occurrence is in sugar beet, and it is this amine present that is behind thè fish-like aroma commonly characterised thè commercial extraction of sugar ffom beet. Likewise, in thè animai body, especially dairy, betaine is capable of transforming into, trimethyl-amine, and it is this which, gives thè fishly smeli to milk produced by cows that have been given eccessive amount of sugar beet by- produets. Amides An essential amides that occur as components of proteins are asparagine and glutamine, which are derivatives of certain amino acids. They occur as ffee amides and play an important role in transamination reactions. Urea is an amide which is thè main end-product of nitrogen metabolism in mammals. In human beings and other primates, urie acid is thè end product of purine metabolism and is found in thè urine. In birds, urie acid is thè principal end-product of nitrogen metabolism and thus corresponds, in its function, to urea in mammals. Nitrates Nitrate is present in certain plants and naturally non-toxic except by reduction to nitrite in a favourable rumen condition that becomes toxic. Oat hay poisoning is traced to thè concentrated amounts of nitrate present in ff esh green oats. There were reports that established thè high levels of nitrate in herbage given heavy dressings of nitrogenous fertilisers. Alkaloids Alkaloids are present only in some plants and many of them have poisonous properties. Their presence is limited to a few orders in thè dicotyledons. Some important alkaloids occurring in plants are quinine (cinchona bark), nicotine (tobacco), conine (hemlock), atropine (deadly nightshade), cocaine (leaves of coca plant), solanine (unripe potatoes and potato sprouts), ricinine (castor plant seeds). Nucleic acids Nucleic acids are high molecular weight compounds consisting of nitrogenous compounds (purines and pyrimidines), a pentose (ribose or deoxyribose) and phosphoric acid. Nucleic acids are thè bedrock in plants and animals as a reservoir 20 UNIVERSITY OF IBADAN LIBRARY of genetic information, and they are thè means by which this information is utilised in thè synthesis of proteins. 1 ) The main pyrimidines found in nucleic acids are cystosine, thymine and uracil. 2) Adenine and guanine are thè principal purine bases present in nucleic acids. 3) Phosphoric acid — if nucleotides such as adenosine are esterified with phosphoric acid they form nucleotides, e.g. Adenosine monophosphate (AMP). 4) Ribose — Nucleotides containing ribose are termed ribonucleic acids (RNA) while those containing deoxyribose are known as deoxyribonucleic acids (DNA). Summary There are non-protein nitrogenous (NPN) compounds that are present in plant and animals. Some of these NPN are highly poisonous primarily or secondarily. For example, amine is only poisonous or toxic under decomposition or fermentation of organic matter (OM). Also, nitrates in certain plants is not toxic but toxic as nitrite in a favourable rumen condition. On thè other hand, certain NPN, e.g. alkaloids are primarily toxic in some plants, e.g. cocaine in thè leaves of coca plant. _________________________ Post-Test 1. What are non-protein nitrogenous (NPN) compounds? 2. List those NPN that are secondary poisonous and state how? 3. Explain why nucleic acids formed thè ‘bedrock’ of living orgamsms. References Lehninger, A.L. (1982). Principles o f Biochemistry. New York: Worth Pubi. McDonald, P., R.A. Edwards, J.F.D. Greenhalgh (1987). Animai nutrition. Fourth edition. London: ELBS, 21 UNIVERSITY OF IBADAN LIBRARY LECTURE FIVE The Chemistry of Carbohydrates I Introduction Carbohydrates make up most of thè organic structure of all plants, as well as being present to some extent in all animals. Carbohydrates in plants are produced by thè processs of photosynthesis (thè most important Chemical reaction in nature). During photosynthesis radiant energy (solar energy) from thè sun is captured by chlorophyll and changed to Chemical energy, which in tum supports formation of glucose from carbon dioxide and water. This overall reaction can be represented by thè equation below. However, thè intermediate biochemical reactions involved are much more 6CO, 6H?0 ■ i unl‘Sh! . r //,0, 60, 2 2 Chlorophyll 6 2 6 2 (Sugar) complex and should be left for an advance course. The animai life is basically dependent on thè process of photosynthesis. Objective In this course, we shall concentrate on thè different courses of carbohydrates, and their Chemical structures and functions. Pre-Test Discuss thè types and functions of carbohydrates. CONTENT What are Carbohydrates? Carbohydrates simply put, means hydrated carbon because many of them can be represented by thè simple stoichoimetric formula (CH20 )n. This formula is an oversimplification because many carbohydrates (saccharides) are modified, and contain amino, sulphate and phosphate groups. 22 UNIVERSITY OF IBADAN LIBRARY Generally speaking, carbohydrates are a group of organic compounds that include sugar and related compounds. However, chemically, carbohydrates are polyhydroxy aldehydes and ketones, or substances which yield them (aldehydes and ketones) upon hydrolysis. In this respect, thè group termed carbohydrates include sugars, starches, cellulose, gums, pectins, saponins, glucosinolates, cyanogenic glucosides, lectins, glycogen, chitin, etc. i Importance of Carbohydrates Carbohydrates are extremely versatile molecules essential to every kind of living organism. Carbohydrates are among thè most abundant constituents of plants and animals. They serve thè following functions: i) As major storehouse of Chemical ènergy, i.e. provision of energy for carrying out life processes. ii) They serve as sources of raw materiale for thè Chemical synthesis, e.g. milk is synthesis from two kinds of carbohydrates namely galactose and glucose. iii) They serve as supportive structural components in plants, e.g. cellulose, lignin, hemicellulose, etc. iv) Carbohydrates are essential in thè genetic control of development and growth of living cells. Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) thè genetic materials contain ribose sugar, a form of carbohydrate. v) Some kinds of carbohydrates protect plants against infections, e.g. polyphenolics, saponins, etc. Some General Properties of Carbohydrates Many of thè carbohydrates may contain thè same number of atoms and thè same kind of groups yet behave differently, i.e. same molecular formula but different structural formulae. Example, thè formula C6H120 6 represents sixteen different simple sugars. The different structural formulae is due to different arrangement of thè constituent groups of thè molecular in space. This phenomenon is called STEREOISOMERISM (space isomerism) and these differently arranged sugars are referred to as “STEREOISOMERS”. An illustration of this phenomenon will be given by examining three of thè sixteen stereoisomers of C6H120 6. These three stereoisomers are glucose, mannose and galactose. 23 UNIVERSITY OF IBADAN LIBRARY 'CHO 'CHO 'CH1O H -JC -O H HO - 2C - H HO -3C - H HO - C - H HO - 3|C - H H - 4C1 - OH H - 4C 1- OH H - 4Ci - H H - fC - OH H - 5C - OH H - 6C1 - OH 6c h 2o h t H 2OH c h 2oh glucose Mannose Galactose A closer look at these structures of mannose and galactose will show that they (mannose and galactose) would have assumed thè structure of glucose but for a change in thè positions of OH group on carbon 2 and 4 for mannose and galactose respectively. The carbon atoms involved are in asterisks. Other structures (stereoiserms) do not exist naturally in nature. Carbohydrates also exhibit a phenomenon called ENANTIOMERS. Enantiomers are compounds with thè same Chemical formula but can exist in two forms — one of thè forms being a mirror image of thè other. This phenomenon is common with monosaccharides because they (monosaccharides) tend to have more than one chiral carbon, which results in their having two types of stereoisomers. An example of this stereoisomer can be illustrated with thè monosaccharides, Threose and Erythrose ni 1c : — o o —I 1 o Ih p I— *c.- —11 - E5FT1 ì i 3c : I i l! IT-TOI c: ‘ h i l - Jci — I l 11 - : - i i HV MV D -Thrcosc L-Thrcosc H H c : =I o <> —- C H - C - lox-l 1 Ih o I c : - T I *rL ' I — — [oird l liHLOl - (C - K H CI H H - C — H H? VIT H>- Erythrose 1— - Erythrose 24 UNIVERSITY OF IBADAN X X L 1 0I 0B 1 -O L - 1 R oX oXARY The enantiomers for Threose and Erythrose are arranged according to thè manner in which thè substituents ai 2 arranged about thè asymmetric carbon atoms. The naming by L and D (for “dextrorotatory” and “Levorotatory”) are according to a convention established by Emil Fisher. The carbohydrates also exhibit thè property of optical activity and therefore exist as optical isomers. When carbohydrates are placed in a POLARIMETER (an instrumeijt for studying thè interaction of polarized light with optically active substances (Fig. 1-) thè resulting light is either circularly polarized to thè right-or left. When thè piane polarized light is rotated clockwise (i.e. to thè right) thè substance is classified as DEXTRORATORY (d-), but when rotated counterclockwise (anticlockwise) (i.e to thè left), thè substance is termed LEVOROTATORY (L-). However, when equal mixtures of d and L substances are mixed (di) thè resultant (RACEMIC) is optically inactive. Rotateci piane Piane polarized eight Monochromatic Light Sample tube Nicol Prism Unpolarized Linearly Circularly polarized Circularly polarized Light (Piane polarized light light light) (right) D (Left) L 25 UNIVERSITY OF IBADAN LIBRARY Summary Carbohydrates make up most of thè organic structures of all plants and to some extent in all animals. Carbohydrates are manufactured by process of photosynthesis—thè most important Chemical reaction in nature. Chemically carbohydrates are polyhydroxy aldehydes and ketones, or substances which yield aldehydes and ketones upon hydrolysis. The term carbohydrdte includes sugars, starches, cellulose, gums, pectins, saponins, glucosinolates, etc. Functionally, carbohydrates serve as a major storehouse of energy, raw materials for synthesis of milk and also supportive structural components. In addition, carbohydrates are essential in synthesis of RNA and DNA — thè genetic materials. Carbohydrates exhibit stereo isomerism. Post-Test 1. What are carbohydrates? 2. List thè importance of carbohydrate to cattle ; ^ 3. Carefully distinguish between glucose, mannose and galactose References Chesworth, J.M., Stuchbury, T. and Scaife, J.R. (1988). Agricultural Biochemistry Ist Edition Published by Chapman and Hull. Maynard, L.A., Loosli, J.K., Hintz, H.F. and Warner, R.G. (1983). Animai Nutrition (7th Edition). Tata McGraw Hill Publishing Company Limited. 26 UNIVERSITY OF IBADAN LIBRARY LECTURE SIX The Chemistry of Carbohydrates II Introduction Carbohydrates play an important role in thè supply of energy, structural rigidity and formation of RNA and DNA in living organisms (plants and animals). The carbohydrates come in different forms (classes) and thè ability of carbohydrates to carry out thè above mentioned functions depends on thè type (class) of carbohydrate. In livestock nutrition, carbohydrates serve as thè major energy sourccs. However, thè ability of livestock to utilize thè carbohydrate will depend on thè typc of carbohydrate and thè type of livestock (whether monogastric or ruminant). It is therefore imperative for us to study thè carbohydrate type available and some of their Chemical reactions. Objectives In this chapter, students will leam thè classes of carbohydrates and their properties. Emphasis will also be placed on thè structures of thè carbohydrates studied. Pre-Test la) What are monosaccharides, oligosaccharides and polysaccharides? b) Give four examples of each of thè classes of carbohydrates listed above. CONTENT Classes of carbohydrates; monosaccharides, oligosaccharides and polysaccharides. Classifìcation of Carbohydrates Carbohydrates are classified into three broad groups, namely: I. Monosaccharides II. Oligosaccharides III. Polysaccharides We will now take each of these carbohydrates (above) and discuss them in 27 UNIVERSITY OF IBADAN LIBRARY details. The type of carbonyl group is denoted by thè prefix of aldo-for an aldehyde and keto-for a ketone, e.g. glyceraldehyde is an aldo-triose. The structures of some common monosaccharides are given below: Trioses (C,) H - C = 0 , H - C = 0 H - C - OH H O - C - H CH;OH CH2OH D-glyceroie L-glycerose Tetroses (C4) H - C = 0 H - C - OH H - C - OH CH2OH D-erythrose Pèntoses (C5) H - C = 0 H - C = O H - C = O H- C- OH H - C -H H - C - OH H- C- OH H- C- OH HO - C - H H- C- OH H- C- OH H - C - OH |1 CH2OH c h2oh CH2OH D-Ribose 2-Deoxy-D-Ribose D-xylose (RNA) (DNA) (Hemicellulose) I. Monosaccharides The monosaccharides are also referred to as simple or monomeric sugars. The monosacchande is thè fundamental unit from which all carbohydrates are formed. Monosaccharides are therefore thè simplest carbohydrates. 28 UNIVERSITY OF IBADAN LIBRARY The monosaccharide can be represented by thè empirical formular (CH20 )n when ‘n ’ a whole number is equal or greater than thè value 3. The smallest molecules usually regarded as monosaccharides are thè trioses with n = 3 (The suffix -ose is commonly used to designate compounds as saccharides). Monosaccharides containing 2 to 10 carbon atoms have been synthesized, and many occur in nature. Naming of Sugars The Chemical names of sugars and many complex carbohydrates end with thè sufftx-ose. They are also named on a basis of thè number of carbon atoms that they contain; tri- for three, and tetra-, petra, hex-, and hept- for 4, 5, 6 and 7, respectively. H - C = O CH;OH HO - C - H C = O HO - C - H HO -C -H HO - C - H H -C - OH CH:OH CH:OH L - Arabinose D - Xylulose (Gums) (Phosphogluconate pathway) H exoses (C 6) (1) CHO CH;OH CHO CHO (2) * HCOH * HCOH HOCH > (3) * HOCH * HOCH * HOCH HOCH | 1 (4) * HCOH * HCOH * HOCH HCOH (5) * CHOH * HCOH * HCOH HCOH 1 1 (6) CH,OH c h 2o h CH2OH CH2OH D-glucose D-fructose D-galactose D-mannose 29 UNIVERSITY OF IBADAN LIBRARY O il - U - Note that all thè hexoses above are aldehyde except fructose which is a ketone. Because of thè presence of asymmetric carbon atoms (labelled with an asterisk) a number of stereoisomers are possible. Some monosaccharides occur in nature while others are synthetic. The hexoses and pentoses are thè most important of thè simple sugars. The monosaccharides or simple sugars are generally well-crystallined solids, soluble in water, and have more or less sweet taste. Pentoses and hexoses with 5 and 6 carbon atoms respectively have thè potential to form very stable ring structures via internai HEMLA.CETAL formation. The bond angles characteristics of carbon and oxygen bonding are such that rings containing fewer than five atoms are strained to some extent, whereas fire- or six-numbered rings are easily formed. In principle, aldotetroses can also form five-numbered ring structure, but they rarely do. Hemiacetals with five-membered rings are called FURANOSES, while those hemiacetals with six-membered rings are called PYRANOSES (figures 2). However, we should note that in cases where either five- or six-membered rings are possible, thè six-membered ring usually predominates. For example, for glucose less than 0.5% of thè furanose forms exist at equilibrium. Why? Reason for this is not yet clear. But furanoses and pyranoses are more realistically represented by pentagons or hexagons as in HAWORTH CONVENTION. In another way thè structures can also be represented as straight chain showing thè acetal bonding as described in thè FISHER PROJECTION (Figure 3). Fructose (C6H,20 6) p-D-glucose in thè pyranose (fructofuranose) (glucopyranose) Fig. 2: Rug structure o f six carbon atom compounds 30 UNIVERSITY OF IBADAN LIBRARY 'C -O H I H - !C - OH HO - ’CI - H O I H - JC - OH I li - 'C------------ I ’CHjOH « - D - Glucose (Fisher projection) II. Oligosaccharides The oligosaccharides contain sugars with 2 -1 0 glucose units joined together by glycosidic bonds. The oligosaccharides are therefore formed by thè combination (coming together) of 2 or more (maximum of 10) of thè monomers. The monomer sugars may be of same sugars or different monomer sugars. Examples of some common oligosaccharides are mentioned below: a) Disaccharides — made up of 2 monomer sugars, e.g. sucrose, maltose, cellubiose. b) Trisaccharides — made up of 3 monomer sugars, e.g. raffinose c) Tetrasacchandes — made up of 4 monomer sugars, e.g. stachyose. d) Pentasaccharides — made up of 5 monomer sugars, e.g. verbascose. The simplest and biologically most important oligosaccharides are thè DISACCHARIDES, made up of glycose units, e.g. sucrose, lactose, maltose, cellubiose, gentiobiose. The types of monomer sugars that make up these disaccharides are shown in Table 1. Table 1: Compo^ition of some disaccharide sugars Disaccharide Structure Sucrose Glucose -Fructose Lactose Galactose - Glucose Trehalose Glucose - Glucose 31 UNIVERSITY OF IBADAN LIBRARY ( A\ - ' , t Maltose Glucose - Glucose Cellubiose Glucose - Glucose Gentiobiose x Glucose - Glucose A look at 'Table 1 shows that glucose appeared as a constituent of all thè disaccharide.- This underscores thè importance of glucose as a substrate in thè nutrition of plants and animals. Secondly, a look at maltose, cellubiose and gentiobiose showed that these disaccharides contain only glucose units. The question now is that how can two glucose units combine to give three different products. This may appear confusing at first. A little explanation is therefore needed at this stage. This will depend firstly on whether thè connecting sugars are a or P type and secondly it will also depend’on thè points at which thè sugars are connected to each other. These points are illustrated by discussing how thè disaccharides are formed from two units of monomers. The disaccharides derive their name from thè fact that they are a combination of two molecules of monosaccharides. Their generai formular, C12H22D ,, indicates that one molecule of water has been eliminated as two monosaccharides combine h 2o C,H,A + C,Hl20 „ -£* C„H„0 „ Formation of Disaccharides Two molecules of simple sugars (monomers) are linked together by an acetal to form a disaccharide. The two simple sugars may either be similar or different. The following features therefore distinguish one disaccharide from another. i) The two specific sugars involved and their stereoconfiguration. (Remember thè stereoisomerism discussed in lecture I). ii) thè carbons involved in thè linkage. Most common linkages are 1 - 1, 1 - 2, 1 - 4 and 1 - 6. iii) thè order (arrangement) of thè two monomers iv) thè anomeric confìguration of thè hydroxyl group on carbin 1 of each glucose unit. The disaccharide with a bond between thè 1 carbon of a - glucose and 4 - carbon of another a - glucose is called a MALTOSE. The bond is called a - 1, 4 32 UNIVERSITY OF IBADAN LIBRARY glycosidic link. If however thè left-hand sugar has been in thè p form before linking then thè compound would be a P-linked disaccharide. The compound of this sort which is comparable to maltose is called a CELLOBIOSE. Lactose, thè sugar found in milkresembles cellobiose but thè left-hand sugar is galactose instead of glucose. The structures of some common disaccharides are shown below: Common disaccharides CIIOII CI 1,011 a) maltose CI 1,011 C1I.O I1 c) Lactose P - galactose a - glucose 33 UNIVERSITY OF IBADAN LIBRARY / " I I ( il I o d) Sucrose il OH Oli li a - glucose (3 - fructose Note; with thè exception of sucrose, thè ring of thè right-hand glucose unit can open exposing a free aldehyde group and giving reducing properties to thè sugars. Also, thè dissaccharides are soluble in water, though to varying levels. Short Notes on some Dissaccahrides Sucrose (Cane Sugar) Sucrose is made up of a combination of one molecule of D-glucose and one molecule of D-fructose. It occurs in sugar cane hence thè synonym “cane sugar” and also in beets (major sources of commercial sugar). Sucrose also occurs in ripe fruits, in tree sap (maple sugar), and in many fruits and vegetables. Sucrose is dextrorotatory but it is not a reducing sugar as it has no free aldehyde or ketone group. When hydrolysed by dilute acid or thè enzyme sucrose, sucrose splits into two constituents monosaccharides. The resulting sugar is levorotatory. Since thè hydrolysis thus results in a change from destrorotation to levorotatum, thè process is called INVERSION and thè mixture of glucose and fructose is often termed INVERT SUGAR. Such a process is thè way by which honey bees convert sucrose of plant nectar to honey. Maltose (Malt Sugar) This disaccharide consists of 2 molecules of a - D - glucose joined together in an a - 1,4 linkage. The position of H on thè number 1 carbon atom molecule (a) is thè a position. Note that thè number 6 carbon atoms are in as configuration. Maltose derives its name from thè fact that it is produced commercially ffom starch by thè action of malt, obtained from germination barley which contains a starch hydrolysing enzyme distaste. 34 UNIVERSITY OF IBADAN LIBRARY Cellobiose Consist of 2 molecules of B - D-glucose joined together in a [3- 1,4 linkage. This linkage is thè fundamental one for thè cellulose molecule and cannot be split by mammalian enzyme. It can be split, however, by microbial and fungal enzymes or acid. Cellobiose does not occur in free form in nature but only as a component of glucose polymers. Lactose (Milk Sugar) This is thè sugar of milk and consists of one molecule of a - D - glucose and one molecule of P - D - galactose, joined in a linkage. This linkage can be separated by thè enzyme lactase or by thè addition of acid. It is a reducing sugar and is only one- sixth as sweet as sucrose. Lactose is of special interest in nutrition, because it makes up ncarly half of thè solids of milk and because it does not occur in nature except as a product of thè mammary gland. Having discussed thè mono-and disaccharides we shall now focus on thè third and last class of carbohydrates — thè polysaccharides. III. Polysaccharides The carbohydrates consisting of 10 or more monosaccharides are referred to as POLYSACCHARIDES. They may be considered as condensation of polymers in which thè monosaccharides (or their derivatives such as amino sugars and uronic acids) are joined together by glycosidic (acetal) linkages. Polysaccharides are also called GLYCANS and they consist of two types namely HOMOGLYCANS and HETEROGLYCANS. Homoglycans are polysaccharides that consist of a single kind of monosaccharide while heteroglycans consist of more than one kind of monosaccharide. Polysaccharides consisting mainly of glucose are called GLUCANS while those consisting of fructose, mannose and xylose alone are referred to as FRUCTANS, MANNANS and XYLANS, respectively. Examples ofhomoglycans are starches, cellulose, glycogen, insulin, chitin, etc. while examples of heteroglycans are gum acacia, pectins, alginic acids, mucopolysaccharides (hyaluronic acid, heparin, chondroitin sulphates). Generally speaking, polysaccharides are insoluble in water but upon hydrolysis by acids or enzymes, they are broken down into various intermediate products and finally their constituent monosaccharide units. In this aspect of thè course we shall be concemed with starch, cellulose and glycogen. Other polysaccharides will be discussed in future. 35 UNIVERSITY OF IBADAN LIBRARY Starch i Storage carbohydrate found in plants. It consist of glucose units. it is ; homoglucan (rememberourearlierdiscussion onhomoglycans!). Starch ; : - ; of a mixture of 2 different types of molecules, amylose and amylopectin Amylose consists of a long chain of glucose units joined by a-1,4 linkages while amylopectin consists of a mixture of a 1,4 links with occasionai a 1, 6 branches (fig 3. )..The branches occur after about 25 straight a 1, 4 bonds. Starches from different sources vary in thè ratio of amylose and amylopectin, in thè size of thè individuai molecules, in generai amylopectin accounts for about 70% of starch. cuoii cu,oh aio» H OH H OH H OH I. 4 link ape Fig. 3 : Structure o f amylose The structure above is thè glucose units of amylose linked in an unbranched chain. The amylose structure can therefore be considered as an expanded maltose structure with a free sugar group on one end. CH.OH CH OH H OH H OH 1. 6 Linkage Fig. 4: Structure o f amylopectin 36 UNIVERSITY OF IBADAN LIBRARY Amylopectin also contains chains of glucose units like those of amylose, also has branches of these glucose chains linked through thè 6 - OH of glucose in thè manner as shown in Fig. 4. The long chains of amylose roll themselves into a stable helix shape which is held in place by hydrogen bonding. The helix is a tube into which other molecules or atoms can fit. One example of this is thè fact that iodine can fit inside thè helix and form a blue coloured complex with amylose, a reaction which is often used to detect thè presence of starch or iodine. The bluer thè colour obtained, thè more thè amount of amylose component of thè starch. Amylose is soluble in hot water while amylopectin is insoluble in hot water. Starches from different plants when viewed microscopically show difference in shapes and sizes (appearances). This property fumishes thè basis for microscopie identification of different types of starches. Some starches show a high degree of hydrogen bonding and such starches are quite resistant to rupture. Tuber starch, such as found in thè potato, is extremely resistant and must be cooked before being utilis'ed by species such as pigs or chickens. Starch type in plants is genetically determined. However, starch modification techniques are available and have applications in thè food industry. Dextrin is an intermediate resulting from thè hydrolysis and digestion of starch as well as thè action of heat on starch. Cellulose This is thè most abundant substance in thè plant kingdom and is a major structural component of plant celi walls. Cellulose is made up of polymerised glucose molecules ranging from 900 - 2,000 molecules. Cellulose is also a glucan. Chemically, cellulose is a polymer of p - 1,4 - linked D - glucose units. As such, thè six carbon atoms are in thè trans position which results in cellulose being fiat, band-like microfibril. Naturai cotton is one of thè purest forms of cellulose. Cellulose is not subject to attack by thè digestive enzymes of man and other monogastrics, hence it is an important source of bulk in thè diets. Contrarily, microbes in thè rumen of ruminants can secrete cellulose enzyme which can degrade cellulose. Cellulose is not soluble in water but soluble in ammonical solution of Cupric hydroxide, HC1 acid solution of zinc chloride. Glycogen This is thè Storage form o f carbohydrates in animals and fungal cells. G lycogen is deposited in thè liver, which acts as a centrai energy Storage organ in many animals. G lycogen is also abundant in muscle tissue, where it is more immediately available 37 UNIVERSITY OF IBADAN LIBRARY for energy release. The structure of glycogen is of D-glucose combined with « - 1 , 4 linkage and an « - 1,6 cross linkage, very similar to that of amylopectin (component of starch moeity) except that thè molecules are iarger and thè cross linkages move frequently (once every 15 or so straight bonds). Glycogen gives a red-brown, red, or at times, violet colour with iodine, and which yields D - glucose upon complete hydrolysis. Summary Carbohydrates are classified into 3 majorgroups namely; monosaccharides, oligosaccharides and polysaccharides, respectively. The monosaccharides are thè simplest forms of sugars and make up oligosaccharides and thè polysaccharides. The carbohydrates can be represented by Chemical and structural formulae. The structural formulae are either represented in straight chain or in ring forms. This is specially represented by thè hexoses (6 - carbon sugars). The carbohydrates are source of energy for animai nutrition. The monosaccharides and oligosaccharides are efficiently metabolised by simple stomach animals. On thè other hand ruminants contain microbes while secrete enzymes capable of degrading cellulose. Glycogen is a polysaccharide found in animai and fungal cells. Glycogen is a Storage form of carbohydrate and readily utilized when there is deficiency of energy. Post-Test la ) What are m onosaccharides, oligosaccharides and polysaccharides? b) U sing necessary Chemical structures give 2 exam ples o f thè classes o f carbohydrates listed in l(a ) above. 2. Write short notes on thè following: a) Glycans b) Starch c) Cellulose Reference Maynard, L.A., Lopsli, J.K., Hintz, H.F. and Warner, R.G. (1983). Animai Nutrition. 7* edition. Published by Tata McGraw Hill Publishing Company Limited. 38 UNIVERSITY OF IBADAN LIBRARY LECTURE SEVEN The Chemistry of Lipids Introduction Lipids are biological substances that are soluble in organic solvents. Apart from bemg structural components of biological membrane, they also play a major role in thè nutrition of thè animai. Just as carbohydrates can supply energy, lipids can also carry out this function. In this chapter, we will focus on functions of lipids, their classification and thè structures of some common lipids. Objectives Students will leam what lipids are, their functions and structures of some lipids. Pre-Test la) What are lipids? b) Discuss thè importance of lipids in thè animai. 2a) Name 3 unsaturated fatty acids. b) Name 3 saturated fatty acids. c) Give thè Chemical structures o f thè fatty acids mentioned in 2(a) and 2(b) above. CONTENT Definition of a lipid, functions of lipids, classes of lipids, naming of fatty acids. Definition of Lipid Lipids are biological molecules that are soluble in organic solvents. Lipids therefore include fats, oils, waxes, and related compounds. Occasionally, thè term lipoid may be used in place of lipid. These two terms are synonymous and therefore can be used interchangeably. 39 UNIVERSITY OF IBADAN LIBRARY Importance of Lipids Lipids ha ve thè following biological functions: i) Certain lipids, fats, serve as efficient reserves for Storage energy. Such lipids are found in thè adipose tissues. ii) Fats serve as carriere for thè fat soluble vitamins. The fat-soluble vitamins are, Vitamins A, D, E and K (A,D,E,K). iii) Lipids constitute thè major structural elements of membranes. When lipid is in combination with a protein thè resulting substance is termed LIPOPROTEIN, i.e. lipid-protein. vi) Fat serves as insulating material in thè subcutaneous tissues around certain organs. v) Cholesterol, an example of a lipid, is a major substance from which Vitamin D and sex hormones are synthesized. Classification of Lipids Bioor classified lipids as follows: i) Simple Lipids — These are esters o f fatty acids with various alcohols. Example of simple lipids include fats (esters of fatty acid with glycerol), waxes. ii) Compound Lipids — These are esters of fatty acids but containing in addition, alcohol and a fatty acid. Examples of compound lipids include phospholipids, e.g. (glycerophospholipids), sphingophospholipids, cerebrosides (glycolipids) — compounds containing thè fatty acids with carbohydrates, containing nitrogen but no phosphoric acid. Other compound lipids include sulpholipids, aminolipids, lipoproteins. iii) Derived Lipids — These are substances derived from thè hydrolysis of simple lipids and compound lipids. The derived lipids include fatty acids, glycerol, steriods, alcohols in addition to glycerol and sterols, fatty aldehydes and ketone bodies. Because glycerides (acylglycerols), cholesterol and cholesteryl esters are unchanged they are also termed neutral lipids. Fatty Acids Fatty acids are a group of aliphatic carboxylic (- COOH) acids, which contains from 2 to 24 or more carbon atoms. Fatty acids are obtained from thè hydrolysis of fats. However, fatty acids can also occur in naturai fats and such fatty acids normally contain an even number of carbon atoms (i.e. from 2-carbon units) and are also striaght-chain derivatives (aliphatic). Fatty acids can either be saturated or unsaturated. We shall elaborate on this shortly. Fatty acids can also be straight-chain or branched. However, thè most 40 UNIVERSITY OF IBADAN LIBRARY abundant types of fatty acid are saturated and unsaturated straight-chain fatty acids. Before we get to discuss how fatty acids are named (nomenclature) let us first look at saturated and unsaturated fatty acids. Saturated Fatty Acids These are fatty acids that do not contain any unsaturated bonds (i.e. having single bonds). The generai formular for thè saturated fatty acid is C„H2n + ,COOH - thè first member of this group is acetic acid. Others will be discussed later. Unsaturated Fatty Acids These are fatty acids that contain one or more doublé bonds (unsaturated bonds). Unsaturated fatty acids with only one doublé bond are called MONOUNSATURATED fatty acids or MONOETHENOID ACIDS. Those with more than one doublé bonds are referred to as POLYUNSATURATED fatty acids (PHFA) or POLYETHENOID. Naming of Fatty Acids (Nomenclature) Genevan System This is thè most frequently used systematic nomenclature. This System is based on naming thè fatty acid after thè hydrocarbon with thè same number of carbon atoms. In this case — oic is substituted for thè final -e in thè name of thè hydrocarbon. This is illustrated with thè examples below: Butan/e becomes butan/oic acid methane becomes methanoic acid But for unsaturated fatty acid — enoic is added in place of -ioc. Carbon atoms are numbered from thè carbonyl carbon (i.e. carbon number 1). The next carbon atom after thè carboxyl carbon (i.e. carbon 2) is also known as thè « - carbon (alpha carbon). Carbon atom number 3 is thè p - carbon (Beta carbon) and end methyl carbon is known as w - carbon (omega carbon). The second convention uses thè number of carbon atoms between thè methyl carbon and thè nearest doublé bond and uses thè n - (n minus) notation. This convention is particularly useful for ìdentifying formulas of fatty acids derived from common precursor fatty acids as A9,12 (18, 2 or C18: 2n - 6). It is conventional to indicate thè position of thè doublé bond by thè following A9, i.e. indicates a doublé bond between carbon atoms 9 and 10 of thè fatty acid. 41 UNIVERSITY OF IBADAN LIBRARY Methyl Carbon Carbonyl Carbon / **CH3 - 3PCH, - 2”CH - ’COOH Monòsaturated fatty acids (CnH2n + 1COOH) Name Formular Occurrence Acetic acid CHjCOOH M ajor end p ro d u c ts o f carbohydrate fermentation by rumen microbes Propionic acid C2H5COOH M ajor end p ro d u c ts o f carbohydrate fermentation by rumen microbes Butyric acid (Butarwic) c 3h 7c o o h In certain fats in small amounts as butter. Fermentation in rumen Caproic (Hexanoic) C5HuCOOH In certain fats in small amounts as butter. Fermentation in rumer Caprylic (Octanoic) c 7h ,5c o o h Butter Capric (Decanoic) c 9h ,9c o o h Butter Lauric (Dodecanvic) C uH23COOH Spermacetic, cinnamon, palm kernel, coconut oils Myristic (Tetradecanoic) c I3h 27c o o h Nutmeg, palm kernel, coconut oils Palmitic (Hexadecanoic) C ì5H31COOH Common in all animai and plant fats Stearic (Octadecanoic) c I7h 35c o o h Common in all animai and plant fats Arachidic (Ficosanoic acid) c I9h 39c o o h Peanut (arachis) oil Othcr higher members also occur in waxes. 42 UNIVERSITY OF IBADAN LIBRARY A few branch-chain saturated fatty acids have also been isolated from both plant and animai sources. The long chain saturated fatty acids have lower rates of absorption than thè shorter chain or thè unsaturated fatty acids in both non- ruminants and thè ruminants. Monosaturated Fatty Acids General formula CnH2n - 1COOH Trivial Name Systematic Name Shorthand Palmitoleic acid C|5 - A9 - hexadeconoic acid A9 C 16 : 1 Oleic acid C,5 - A9 - octadecenoic acid A9 C I8 : 1 Gondoic acid C |5 - A11 - eicosenoic acid A" C20 : 1 Erucic acid C15 - A13 docosanoic acid A13 C22 : 1 Nervonic acid C |5 - A15 - tetrasenoic acid A15 C24 : 1 Palmitoleic and oleic acids are more nutritional signifìcance than other mentioned above. Polyunsaturad Fatty Acids 2 doublé bonds General formular CnH2ll - 3COOH e.g. Linoleic acid (C I8 : 2; 9, 12). 3 doublé bonds General formular C„H2n - 5COOH e.g. Linolenic acid (C18 : 3; 9, 12, 15). 4 doublé bonds General formular CnH2n - 7COOH e.g. Arachidonic acid (C20 : 4; 5, 8, 11, 14). Linoleic acid C , j - A9,12 - Octadecadienoic acid A9,I2(C 18:2) 8 Unoleic acid Cl5 - A6,9,12 - Octadecatrienoic acid A6,9,12 (CI8 : 3) 43 UNIVERSITY OF IBADAN LIBRARY « - linolenic acid C15 - A9,12,15 - octadecatrienoic acid A9, l2,15 (CI8 : 3) Arachidonic acid C15 - A5,8 " '14 - eicosatetrempoc acid a5,8 "' l4(C20 : 4) Linoleic, linolenic and arachidonic acids are called ESSENTIAL FATTY ACIDS because animals are unable to synthesis (de novo) by themselves - for this reason they must be included in thè diets. C15 and Trans Confìgurations The polyunsaturated fatty acids also exhibit isomerism just as thè carbohydrates do. But in thè case of polyunsaturated fatty acids (PUFA) thè isomerism depends on thè orientation of atoms or groups around thè axis of thè doublé bonds. These two forms of isomerisms are described as C15 and trans confìgurations. As a generai rule, when thè H atoms are found on thè same sides of a doublé bond this is referred to as C,5, while if thè fi atoms are found on different sides of thè doublé bond. this is referred to as trans. (Fig. X). H H H C = C — — C H C|5 trans The doublé bonds in rnost naturally occurring unsaturated fatty acids have thè Cj5 - configuration, although fatty acids with trans doublé bonds are found in bacterial lipids. PUFAS with a combination of both C15 and trans doublé bonds are produced from C15 unsaturated fatty acids by Chemical hydrogenation of vegetable oils, during thè manufacture of margarines and during biohydrogenation of dictary PUFAS in rumen of ruminant animals. Branched Chain Fatty Acids This term is normally reserved for fatty acids which contain one or more methyl (aid rarely ethyl) substituents along thè carbon chain. Many microorganisms contain branch-chain fatty acids which are mainly iso and anteiso type. CH, - CH - (CH2)n - COOH CH, - CH, - CH - (CH,)nCOOI 1 CH, CH, Iso-branched fatty acids Anteiso-branched fatty acids Fig. Y 44 UNIVERSITY OF IBADAN LIBRARY The fatty acid is Iso- type if thè methyl (branch) is on thè same carbon atom as thè last methyl group of thè fatty acid. It is anteiso - type if thè methyl group (branch) is found on any carbon atom other than thè one on which thè last methyl group is attached (See Fig. Y). These fatty acids are typical of most gram positive and sene gram-negative organisms. Trace qualities of iso and anteiso fatty acids (o.l - 0.3%) are found in ruminano animai fat deposits. They arise as a result of thè digestion and absorption of lipids from thè rumen microorganisms as they pass through thè small intestine. When certain unusual diets are provided, thè proportion of branch-chain fatty acids in sheep and goat fat can be greatly increased. Summary Lipids are biological molecules that are soluble in organic solvents. Lipids play important role as sources of stored energy, structural components of biological membranes. Lipids are classified into three major groups namely; simple, compound and derived lipids. Fatty acids are obtained when fats are hydrolysed and they can be foods or synthesized deinovo. Fatty acids are either saturated or unsaturated or short or, long or straight or branched-chained. The saturated fatty acids contain single bonds and examples are acetic, propionic, butyric, stearic, arachidic acids, etc. while thè long chain polyunsaturated fatty acids (PUFAS) contain one or more doublé bonds. Examples of PUFAS are palmitoleic, oleic, linoleic, linolenic and arachidonic acids. The last three PUFAS (linoleic, linolenic and arachidonic acids) are classified as essential fatty acids because thè body cannot synthesize enough hence they must be included in thè diets. Post-Test la) What are lipids? b) Discuss thè importance of lipids in livestock. 2a) What are saturated and unsaturated fatty acids? b) Give thè Chemical structures o f thè fatty acids mentioned in 2(a) above. 3. Write short notes on thè following: i) C |5 and trans fatty acids ii) branch-chain fatty acids 45 UNIVERSITY O IBADAN LIBRARY References Chessworth, J.M.; Stuchbury, T. and Scaife, J.R. (1998). Agricultural Biochemistry. Published by Chapman and Hall. l st edition Maynard, L.A., Loosli, J.K., Hintz, H.F. and Warner, R.G. (1983). Animai Nutrition. 7th edition. Published by Tata McGraw Hill Publishing Company Limited. Zubay, G. (1993). Biochemistry. 3rd edition. Published by Wm. C. Brown Publishers. 46 UNIVERSITY OF IBADAN LIBRARY LECTURE EIGHT Introduction to Minerals in Animai Nutrition Introduction Minerals are indispensable part of a complete diet of farm animals. In this lecture, dictary essential minerals functions, factors affecting thè requirements and sources will be discussed. Objectives At thè end of this lecture, students should be able to: 1) Define essential and non-essential minerals. 2) List essential functions of minerals. 3) Enumerate factors that affect minerals requirements by thè animals. 4) Identify thè major sources of minerals. Pre-Test 1) What are thè essential minerals. 2) State thè roles played by thè minerals in thè body of animals. 3) Enumerate factors that affect minerals requirements by thè animals. CONTENT What are Essential Minerals Essential minerals are those minerals recognised to carry out vital roles and which must be prcscnt in thè feed. About forty minerals have been discovered to occur naturally in thè tissues of animals and plants. Out of these forty, thè dietary essential minerals are those that have been shown by research to have essential metabolic roles in thè body. The proof that each of these elements is essential rests upon experiments with one or more species. If thè experimental animals develop deficiency symptoms, thè omitted minerai in thè diet is considered to be essential to thè animals diet. There are twenty-seven basic dietary essential minerals that have been recognised, it includes: calcium, phosphorous, magnesium, sodium, potassium, chlorine, sulphur, manganese, iron, copper, iodine, zinc, flourine, vanadium, cobalt, molybdenum, selenium, chromium, nickel, Silicon and tin. 47 UNIVERSITY OF IBADAN LIBRARY Fundamental Roles of Minerals 1) A very prominent function is in thè formation of skeletal trame work. The skeletons of thè vertebrates are macie up of minerals especially Ca and P as constituents of bones and teeth, they give rigidity and strength to thè skeletal structures. 2) Minerals are constituents of thè soft tissues, example is in phospholipids that are.present in protoplasm. They are components of body fluids, e.g. iron bond to protein in thè blood. 3) The acidity and alkalinity of digestive juices are maintained by minerals and thè acidity arises from hydrochloric acid which is formed from sodium chloride. 4) Many of their vital functions are due to an ionie inter-relationship which finds expression in thè terms “antagonistic action” and “balanced solution”. For example a certain balance between Ca, Na, and K in thè fluid which bathes thè heart muscle is essential for thè normal relaxation and contraction which constitutes its beatings. 5) Minerals are important in thè activation of many enzymes and hormones. 6) Minerai salts are sometimes fed to dairy and feedlot cattle beyond thè established requirements because in their role as buffers, thè salts have been reported to improve feed intake, milk production, milk composition and animai health. Minerai salts used as buffers control excess hydrogen ion concentration in thè rumen, intestines, tissues and body fluids or increase thè rate of passage of fluids from thè rumen or both. Factors Affecting Minerai Requirements Many factors determines thè utilization of minerals: a) Inter-relationship among minerals or relationship between minerals and organic fractions may result in enhanced or decreased minerai utilization. Because of thè many inter-relationships among minerals, almost any minerals, may influence directly or indirectly thè utilization of any other minerai. b) The actual amount of minerai in thè diet may also influence utilization. For example if thè diet contains more Ca than that required, thè efficiency of absorption is usually decreased c) The minerals status of thè animai may also influence absorption. A magnesium deficient animals is more efficient in thè absorption of magnesium better than animai with sufficient magnesium Stores. d) The form of thè minerals is also an important determinant of utilization. Iron oxide is not available but ferrous sulphate can be readily utilized. 48 UNIVERSITY OF IBADAN LIBRARY e) Many genetic-nutrition relationships have also been demonstrated. Examples of thè extreme genetic effects are shown by one strani of mice that requires a high dietary level of Cu and by another stram of mice that requires a very high level of Mn. A stram of cattle that has a genetic defect in Zn metabolism has been identified. On thè other hand, a strain of mice that is resistant to Zn depletion has been reported. f) Many1 more subtle differences exists. The copper requirements of merino sheep is reported to be 1 to 2 ppm higher than that for thè British breeds. g) Changes in management practices may also influence thè minerals requirement. For example, thè Ca nutrition of growing pigs has been studied at many experiments stations but there is stili disagreement as to thè optimum dietary level. Sources of Minerals The minerai content of plants depends largely on thè minerai content and pH of thè soil in which thè plants are grown. Many soils are deficient in specific minerals, and crops raised on these soils have same minerai deficiencies. Plants’ Ca and P contents are especially important since animals need fairly large amounts of Ca and P. Other plants usually contain minute amounts of Ca or levels that are lower than animals need. Seeds are low in Ca but contain high level of P. Leaves contain higher levels of both Ca and P than stems. The main minerai in bone are Ca Phosphate and carbonate. Small quantities of Mg, Na, Sr, Pb, cifrate, flouride hydroxide and sulphate are present in thè bone. Minerai Supplements As mentioned earlier in our lecture, in certain parts of thè world, thè soils may be insufficient in one or more minerals that animals need and therefore, thè plants grown in those soils are minerai defìcient. However, for animals to survive in these areas, their rations must include minerals fortifìcation. When selecting a minerai supplement one should consider its:- 1) Minerai composition. 2) Availability in thè immediate environment. 3) Cost per unit of minerai compare to other supplements. 49 UNIVERSITY OF IBADAN LIBRARY Summary Minerai elements are solid cristalline, Chemical elements that cannot be decomposed and synthesized by ordinary Chemical reactions. They are present in both plants and animals to execute specific functions. The amount to be required by animals is largely determined by certain inherent factors. Post-Test 1) Differentiate between essential and non essential minerals. 2) What are thè functions of minerals to farm animals? 3) State thè factors that determine thè minerai requirements by thè livestock. References Alien, D.T., E.R. Harlan and R.G. Will (1986) A Guide to thè Feeding and Nutrition ofRuminants in thè Tropics. U.S.A.: Winrock International Institute for Agricultural Development Petit Jean Mountain Morrilton, AR 72110. Anke, M.A. Hennig, M.Grun, M. Partschelfield, B. Groppel, and H. Ludke (1976). Arsenic, a New Essential Trace Element, Archiv. Tierem-ahrung. 26:742- 743 Babayemi, O.J., A.O. Akinsoyimi, O.A. Isah, A.A. Adeloye, M.A. Bamikole and M.K. Adewumi (1999). Effect o f Magnesium Supplement on Performance Characteristics ofLactating West Africa Dwarf Goats. Trop. Animai Prod. Invest. 2:61-68. Maynard, L.A. J.K. Loosh, F.H. Harold and G.W. Richard (1983). Animai Nutrition Seventh Edition. Tata McGraw-Hill Publishing Company Limited. 50 UNIVERSITY OF IBADAN LIBRARY LECTURE NINE Macrò- and Micro-Minerals in Animai Nutrition Introduction In thè last lecture, twenty-one minerai elements were listed and tagged “essential elements”. In this lecture, thè twenty-one elements will be grouped into macro (major) and micro (trace) minerals. Also, thè specific functions of some macro and micro minerals shall be highlighted. Objectives At thè end of this lecture, students should be able to define macro and micro minerals. In addition, you should be able to give some examples, functions and deficiency symptoms of macro and micro minerals. Pre-Test 1. Differentiate between major and trace minerai 2. What are thè functions of calcium, phosphorus, magnesium, sodium, sulfur and iron? 3. List thè deficiency symptoms of Ca, P, Mg,Na, sand, Fe. CONTENT Macro-minerals Macro minerai, also called major element are essential minerals that are required in large amount by thè animals. These include calcium, phosphorus, magnesium, sodium, potassium sulfur and chlorine. Micro-minerals Micro minerals (trace elements) are those that animals need in small amounts but that are indispensable to animals productivity and health. Such minerals include 51 UNIVERSITY OF IBADAN LIBRARY I manganese, iron, copper, lodine, flourine, vanadium, cobalt, molybdenum, chromium, Tin, N ickel and Silicon; some o f these trace elem ents could be potentially toxic i f used in large quantities. Specific Functions and Deficiencies of Minerals Calcium Calcium is thè most abundant minerai in thè body of thè animals with over 99% of it present in thè bones and teeth. It is an important constituent of most living cells and tissue fluids, it functions in blood coagulation, bone formation, homostatic relations and as enzyme co-factors. Calcium defìciency a) Rickets: In young growing animals, bone growth is affected as sub normal calcification of bone occurs. Thus thè joints become swollen, stiffness and lameness of thè limb. Such deformations are seen in thè chicken breasts, arched back in calves and bowed legs in humans. b) Osteomalacia: This occurs in mature vertebrates. The bones become weak, porous and soft. They break readily hence fractures are common in farm animals and human suffering ffom osteomalacia. In pregnant sows, thè fractured vertebrae may pinch thè spinai cord leading to paralysis. c) Osteoporocis: There is a decrease in thè absolute amount bone in thè skeleton. The rate of bone formation may be normal but increased bone resorption occur in attempt to maintain blood, calcium. Phosphorus A part from thè large amounts of phosphorus in thè bones and teeth, a range of 20- 25% of P in thè body is found in thè extracellular soft tissues. The major functions of P are:- 1. Needed for bone and teeth formation. 2. Carbohydrate metabolism as sugar phosphate, adenosine phosphates and creatine phosphate. 3. In lipid metabolism as it is essential for thè formation of lecithin. 4. Formation of phospho lipid that are essential components of nerve tissues. 5. Formation of nucleoproteins of thè chromatin material of genetic importance. 6. Regulate acid-base balance. 52 UNIVERSITY OF IBADAN LIBRARY Phosphorus Deficiency Rickets in young growing animals and ostcomalacia in thè adult. In rickets due to phosphorus deficiency, reduction occurs in blood level phosphorus. Depraved appetite called “Pica” also occur in cattle. The animals eat woods, rags, bones, rocks. They have rough hair coat and become emaciated. Reproductive disorders, reduced growth and reduced milk production can also occur in cattle. • Magnesiutn The skeleton contains 60% of thè Mg found in thè body. Magnesium functions in relation to enzyme is several ways. a) Component of an enzyme. Metallo proteins contain inorganic elements. Arginase that breaks arginine into omithine and urea contains Mg as a component of its molecules. b) Activator of Enzyme; for example, kinase and mutases that catalyse phosphorylation by ATP and molecular rearrangement respectively require magnesium. c) Enzyme inactivator. In muscles, myosin ATP is activated by Ca but in activated by Mg contrast with actomyosin ATP. Magnesium Deficiency Magnesium deficiency can be due to low intake. However, trace elements studies show how absorption as low as 10-20% in some cases, from feeds and forages. Results are:- 1. Vasodilation with reduced blood pressure 2. Hyperirritability and 3.. Tetany followed by death “Grass staggers”, “Grass tetany” and Magnesium tetany are used for Mg deficiency in adult ruminants. Sodium Sodium is supplied to animals mainly in thè form of Nacl. Most of thè feeds and forages are low in Na. However, plants that grow in alkaline soil have fair amounts. Two major functions of Na are: a) Regulation of osmotic pressure b) Maintenance of acid-base balance A 53 UNIVERSITY OF IBADAN LIBRARY Sodium Deficiency 1. There is reduction of growth 2. Reduced utilization of protein and energy 3. Lowered egg production in poultry 4. In laboratory animals, there is reproductive disturbances Potassium Potassium is found abundantly in plants and animals. It functions in thè regulation of intracellular osmotic pressure, it regulates intracellular acid- base balance, stimulates muscular irritability like Na, and take part in thè metabolism of proteins and carbohydrates. Potassium [k+] and sodium [Na+] in adrenal arterial - blood are important regulators of aldosterone secretion potassium is also important in thè pyravic kinase reaction. Potassium Deficiency When hypo potassemia occurs, thè generai effects are muscular weakness, lethargy, anorexia, myocardial degenerative changes, pulmonary oedema, peripheral paralysis. Chlorine Supplied to animals mainly as Nacl like Na, CI is present biologically in ionie form. The functions of chlorine include: 1. Regulation of osmotic pressure 2. Acid- base equilibrium 3. Chief anion of gastric juice that plays major roles in di gesti on and absorption of foods and feeds. Deficiency of Chlorine Animals deficient of chlorine exhibit decreased appetite, reduced growth rate, ' lowered milk production, feather picking and cannibalism in poultry. There is also heamoconcentration and retention of nitrogenous waste produets. Sulphur Found mainly in organic form as components of proteins (cysteine, cystine and methionine). In thè hormone insulin in glutathione, thiamine, biotin and lipoic acid. In ruminants traces of inorganic S tends to improve thè utilization of urea as a Nitrogen sources. Large inorganic S intake is injurious to these animals. The rumen microflora produce H2S which is absorbed and then causes disturbances. 54 UNIVERSITY OF IBADAN LIBRARY Manganese Found in fairly Constant amounts in plants and animals. Manganese functions as thè activator of many enzymes systems. The major ones are (a) pyravate carbonylase which contains thè minerals and Mn functions in thè trans carboxylation phase of enzymatic reactions (b) In thè synthesis of micopoly saccharine of cartilage, Mn act as a catalyst in thè glucosamine-serine linkages. Others are bone phosphatase, muscle adenosine - tri-phoshate, peptidases and choline esterases. Mn is needed for normal reproduction in mammals. Defìciency of Manganese In defìciency States, thè sexual maturity of thè female is delayed, irregular ovulation and weak young ones are produced. In males, testicular degeneration leads to sterility. In cattle there is poor growth, leg disorders, poor fertility and ffequent abortion. In pigs, thè defìciency symptoms are poor bone growth, shortening of leg bones, enlarged hocks muscular weakness, increase back fat and irregular oestrus. In poultry, slipped tendon, malformation of bones of leg, reduced egg shell thickness and reduced hatcherbility. Iron Iron is present in small amount, 70% of which is found in thè haemoglobin, thè remainder is found mainly in thè liver, spleen, bone-marrow, plasma myoglobin and various oxidation reduction enzymes. Iron functions as respiration pigments (haemoglobin, myoglobin) and in enzyme systems. Defìciency of Iron More than half of iron in thè body is found in haemoglobin and thè formation of pigment is affected by Fe defìciency. Anaemia is thè result. Iron defìciency is not common in ruminants. Iron defìciency in sheep and cattle causes depraved appetite (pica) similar to phosphorus defìciency. It is characterised by diarrhoea, loss of appetite and anaemia. Copper Copper like Fe is needed for haemoglobin formation. Like Fe, Cu is stored in thè liver but smaller amounts are stored in thè brain, bone marrow, spleen, heart and kidneys. Like Fe, Cu may also be components of enzymes systems especially oxidation reduction systems. However, Cu also function in thè neurological systems. 55 UNIVERSITY OF IBADAN LIBRARY Defìciency of Copper Anaemia results from low intake of either Cu or Fe. Other results are depresseci growth bone disorders, depigmentation of hair and wool, demyelination of spinai cord and lesion in thè brain. There is muscular inco-ordination of gastrointestinal disturbances and diarrhoea.. Young lambs tends to be more susceptible to neonatal ataxia or sway back. Fading disease in grazing cattle is an atrophy of thè myocardium with replacement fibrosis. The animai staggers, falls and sudden death tends to ensue due to acute heart failure. Peat scours in cattle is due to low Cu and high molybdenum. In cattle Cu defìciency delays or depresses ocstrus thereby decreasing fertility. In poultry, hatchability is reduced and embryonic abnormalities may occur. Copper functions as a growth promotant as it has antibacterial properties against a broad spectrum of organism.. Zinc Very small amounts of zinc are needed by animals and many plants contain zinc adequately. The major role of Zn is as component of thè enzyme carbonio anhydrase. It is also present in metallo enzymes like pancreatic carboxy-peptidase, alkaline phosphatase, various dehydrogenase as well as tryptophan desmolase. Zn is also a cofactor in enzymes like originase enolase, peptidases, camosinase and oxaloacetic decarboxy lase. Defìciency of Zn The defìciency of Zn results in reduced appetite, retarded growth, gross lesions in thè epithelial tissues hence poor reproductive organ development. In pigs, there is skin lesions on thè legs and belly. In poultry, there is poor feathering. In ruminants, there is disorder of thè hair coats and low milk production. Summary Minerals although nutritionally required in smaller amounts are essential for maintenance and production purposes by thè livestock. However thè major and trace minerals are needed by thè body in large and small amount respectively. Generally, deficiencies of most minerals are shown by a reduced appetite and production, slow growth and occasionally death. 56 UNIVERSITY OF IBADAN LIBRARY Post-Test 1 Differentiate between major and trace minerals. 2. What are functions of calcium and phospherus, magnesium sulfur and iron to livestock. 3. List thè deficiency symptoms of Ca, P, Mg, Na, S and Fe. Referenees Menecty, G.R and H.D. Battarec (1976). Sodium and Potassium in Present Knowledge in Nutrition, 4th ed. New York: .Nutrition foundation. Pamp, D.E., R.O. Goodrich, and J.C Meiske (1976) A Review o f thè Practice o f Feeding Minerals Free Choice, World Rev. Animai prod; 12: 13-31. Posuer, A.S. (1973). Bone Minerai on thè Molecular Level, fed; proc., 32. Underwood, E, J ( 1977). Trace Elements in Human and Animai Nutrition, 4lh ed; New York: Academic Press. 57 UNIVERSITY OF IBADAN LIBRARY LECTURE TEN The Vitamins Introduction The vitamins are part of a complete diet although needed in only minute amounts but essential and which deficiency could speli a doom for farm animals. Although thè discovery of thè vitamins dates from thè beginning of thè twentieth century, thè association of certain diseases with dietary deficiencies had been recognised much earlier. The administration of cod-liver óil for example, in preventing rickets has long been appreciated. It was also discovered by thè end of nineteenth century that beri-beri, a disease caused by vitamin B-complex could be cured by giving brown rice grain rather than polished rice. Objective At thè end of this lecture, students should be able to define and classify vitamins with examples. They should also be able to state functions óf thè specific vitamins and list their deficiency symptoms. Pre-Test 1) What are vitamins? 2) Classify vitamins with specific examples. 3) What are thè functions and deficiency symptoms of vitamins A,D,E,K and B- complex? CONTENT What are Vitamins? Vitamins are pure Chemical compounds that livestocks require in very small amounts for growth, maintenance, reproduction and lactation. They differ from other nutrients in that they do not build body tissues but are components of certain enzyme and hormone systems and thus are essential for thè normal life processes. Some vitamins are metabolic essential for animals but are not considered as dietary essential because sufficient amounts are synthesized in thè body to meet 58 UNIVERSITY OF IBADAN LIBRARY requirements. For easy understanding and comprehension, vitamins are naturally divided into two groups of fat and water soluble. Fat-Soluble Vitamins Fat soluble vitamins may be stored where fat is deposited and thè Storage increases with intake. The fat-soluble vitamins regulate metabolism of structural unit. The fat- soluble vitamins include vitamins A,D,E and K. Vitamin A Vitamin A, known chemically as retinol, is an ùnsaturated monohydric alcohol with thè following structural formula: There is no animai that does not require a dietary source of vitamin A. Liver is a good source of vitamin A. Other animai spurces are cod-liver oil, egg yolk and milk fat. Plants are said not to contain thè actual vitamin A but its precusor, carotene. Carotene is a provitamin A because thè body can transform it into thè active vitamin. The carotenoids present in thè food get changed to vitamin A within thè intestinal wall. Excess vitamin A is stored in thè liver. Vitamin A affects vision and a necessity for normal bone development. It helps to keep epithelial tissues healthy and functional. The main deficiency disorders of vitamin A in animals include: a) Loss of appetite, inhibited growth, increased susceptibility to infection and death. b) The skin is dry, scaly and poor hair production. c) Night blindness d Respiratory tract, that is extensive keratinisation of lining cells, loss of ciliary epithelium. e) Digestive tract (Keratinisation of mucous membrane, loss of gland activities, poor absorption, infections). 59 UNIVERSITY OF IBADAN LIBRARY f) Urinary tract (Metaplasia of epithelium and increased tendency to stone formation) g) Bones (There is overgrowth of porous bone tissue resulting in nerve compression). h) Male, severe degeneration of ovary, decline in egg production by poultry and decreased fertility. Infection of genital tract. Vitamin D There are many forms of vitamin D, but thè two outstanding forms are ergocalciferol (D2) and cholecalciferol (D3). Incorporation of Ca and P into bone matrix is dependent on adequate supply of vitamin D. The vitamin stimulates absorption of Ca and P from thè intestinal lumen. It also stimulates thè reabsorption of Ca+P in thè renai tubules. If vitamin D is not present, rickets develop or thè bones demineralize. Osteomalacia due to vitamin D deficiency is not common in farm animals. In poultry, deficiency of vitamin D causes thè bones and beak to become soft and rubbery. The need to supplement thè rations of ruminants with vitamin D is not so great as that for pigs and poultry. Vitamin D2 (ergocalciferol) 60 UNIVERSITY OF IBADAN LIBRARY Many fish oils, especially cod-liver oil and sun cured legume hays are good sources of vitamin D. Growing plants have no vitamin D, but vitamin D2 is formed by thè irradiation of plant ergosterol by thè sun’s rays after thè plant is cut. Animals kept outside thè pen receive enough vitamin D3. The ultraviolet rays convert a precusor into D3 to meet thè animals needs, so thè sun is a valuable vitamin source in thè tropics. Vitamin E There are eight known forms of vitamin E that exist in nature, which can be grouped into «, p, Y and 8-tocopherols. Out of these, a-tocopherol is thè most biologically active and most widely occurring everywhere. Vitamin E is a powerful antioxidant in thè lining tissues, particularly for lips. It protects other nutrients from oxidative destruction. Vitamin E is essential for reproduction in several species. Testicular degeneration has been reported in vitamin E-deficient pigs and rabbits. The vitamin can prevent and cure “stiff-lamb” disease, which is characterizedby stiffness and dystrophic lesions. Chronic vitamin E deficiency has been noted to produce, in rabbits, lambs, poultry and cattle, electrocardiogram changes which are considered to reflect tieart muscle injury. Vitamin E is abundant in whole cereal grains, in thè germ, and in by-products that contain thè germ. Green forages are excellent sources. Since vitamin E deteriorates easily, rancid feeds usually have none. Vitamin K A number of compounds posses vitamin K activity, but thè two outstanding compounds naturally occurring are vitamins K, (Phylloquinone), found in green plants, and K2 (menaquinone), which is a product ofbacterial growth. Menaquinone is thè metabolically active form of thè vitamin. 61 UNIVERSITY OF IBADAN LIBRARY Menaquinone Vitamin K is usually prescnt in adequate amounts in dietary sources. There is also an intestinal synthesis of thè vitamin. Physiologically, vitamin K is usually needed for thè production of some factors in thè plasma needed for blood coagulation. These are proteins formed in thè liver in thè presence of minute quantities of vitamin K. Deftciency of vitamin K is usually in adult human beings. But inadequate intake and production cause haemorrhagic disease of thè babies. Milk is a very poor source of vitamin K. Calves and piglets may occasionally develop bleeding at mucous membranes or into organs. This is prevented by vitamin K administration. In chicks and growers, a deficiency results in generai weakness, rough plumage, paleness and icteric colouration of thè comb, wattles and eyelids as a result of anaemia. Water Soluble Vitamins The water soluble vitamins are concemed with reactions dealing with energy transfer. Water soluble vitamins must be consumed regularly in thè ration and in adequate amounts. The water-soluble vitamins include B-complex and vitamin C. Vitamin B, (Thiamin) Thiamin chloride 62 UNIVERSITY OF IBADAN LIBRARY Thiamin is widely distributed in foods. Brewers’ yeast is a rich source. The vitamin is concentrated in thè germ of cereal grain and is also present in thè aleurone layer. Other sources are beans, peas and green leafy crops. Animai products rich in thiamin include egg yolk, liver, kidney and pork muscle. Vitamin B, is present in almost all living tissues thus reflecting its significance in carbohydrate metabolism. The deficiency symptoms of vitamin B, include: 1) General condition in terms of loss of appetite, decreased growth, weight loss, generai weakness, lowered temperature. 2) Nervous System (paralysis). 3) Slowing of pulse and respiration, fatty degeneration of heart muscle fibre. 4) Diarrhoea and intestinal atomy. 5) Inhibition of testicular development, ovarian atrophy, premature birth and high neonatal mortality. Vitamin B2 (Riboflavin) Riboflavin is stored in small quantities in thè liver, spleen, kidney and cardiac muscle. HO OH OH I I I CH ,- C - (j: - C - CH,OH ! H H H N N The vitamin B2 occurs in all biological materials. It functions as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) as components of thè flavin enzymes catalyzing hydrogen transfer. The flavin enzymes of thè respiratory chain participate in thè metabolism of carbohydrates, amino acids and fatty acids. Typical deficiency symptoms of riboflavin are seen in thè skin and mucous membranes with inflamation at thè interphase between thè skin and mucous membrane at several body apertures e.g inflamation of thè mouth and nasal mucous membranes, fissures at thè comers of thè mouth and eye lids. Atrophy, oedema and 63 UNIVERSITY OF IBADAN LIBRARY ìnflamation of thè mucous membranes o f thè digestive tract result in difficulties in swallowing, disorders in food absorption and diarrhoea in pigs and chicken. In laying birds hatchabiìity of incubated eggs is first reduced, followed by fall in egg production. Nicotinamide This vitamin is thè amide derivative of nicotinic acid and it is thè form in which it functions in thè body. Nicotinamide is a stable vitamin and is not easily destroyed by heat, acids, alkalis, or by oxidation. CONH Nicotinamide Deficiency symptoms of nicotinamide are shown and characterised by severe metabolic disorders in thè skin and thè digestive organs. There is Ìnflamation and ulceration of thè mucous membranes of thè tongue, mouth, oesophagus. Also, there is dark pigmentation of thè edges and tips of thè tongue (black tongue disease). In poultry, thè bones, especially thè femur, become deformed and curved. The blood and vascular System is affected in pigs and fur-bearing animals, normocytic anaemia develops. Vitamin B6 There are three interconvertible forms of vitamin B6 occurring is thè body which include pyridoxine, pyridoxal and pyridoxamine. c h 2o h c h o c h 2n h 2 Pyridoxine Pyridoxal Pyridoxamine 64 UNIVERSITY OF IBADAN LIBRARY The vitamin is widely distributed, and yeast, liver, milk, pulses and cereal grains are rich sources. Vitamin B6 functions in several enzyme Systems concemed in protein metabolism. Its deficiency symptoms include poor appetite, slow growth and poor feed utilization by pigs and poultry. In rabbits, there are flakes formed on thè skin of thè ears, nose and paws. In pigs, thè coat looks rough and brown. The calf suffers loss of hair and poor feathering in poultry. There is also a fall in poultry egg production, lowered hatchability, high embryonic mortality in second week. Pantothenic acid Pantothenic acid is ubiquitously available in nature. Some good sources of thè vitamin are egg yolk, liver, groundnuts, peas, yeast, molasses and cereal grains. CH3 OH HOCH2 - C - CH - CGNHCH2CH2COOH c h 3 Pantothenic acid Pantothenic acid is a vitamin essential in thè synthesis and catabolism of fats and thè synthesis of steroids. These various roles of thè vitamin serve to illustrate thè fact that it plays an essential role in many cellular reactions. The main lesions of pantothenic acid deficiency involve thè nervous System, thè adrenal cortex and skin. Poor growth also occurs. In pigs a high stepping action with thè hind legs (goose-stepping) often accompanied by a scabby dermatities around thè eyes and snout occurs. In most other animals, there is alopecia after loss of hair pigment. Folacin Folacin is a derivative of folic acid denoted by thè following formula: Folic Acid 65 UNIVERSITY OF IBADAN LIBRARY Folacin is an antianaemia factor. It is widely distributed in nature; green leafy materials, cereals, extracted oilseed meals and animai protein meals are rich sources. The vitamin plays a basic biochemical role in thè transfer of simple-carbon units in various reactions. There is increased demands for folic acid during pregnancy as thè foetus withdraws thè vitamin from thè mother. Hence folic acid, proteins and iron are considered important for thè expectant mothers. Biotin The structure of biotin is written below. O II / C\ HN NH I [ H C----- CH I I H,C CH - (CHJ, - COOH \ s / All cells contain some biotin but larger concentration in thè liver and kidneys. Biochemically, biotin participates in carboxylation reaction by causing biological “activation” of carbon-dioxide. Biotin is widely distributed in foods; liver, yeast, milk and vegetables are rich sources. In poultry, thè deficiency of biotin results in impaired growth, dry and brittle feathers, dermatitis and perosin. Eggs from biotin deficient birds have poor hatchability and embryonic malformations. In pigs, mucous membranes are affected resulting in furry tongue. Choline Illustrated below is thè structure of our next vitamin known as choline. Choline can largely be obtained from yeast, egg yolk, green leafy vegetables or other green leafy materials and cereals. CH3 + CH3- N - C H 2CH2OH c h 3 66 UNIVERSITY OF IBADAN LIBRARY Choline is a vital structural component of animai body tissues. It is a constituent of lecithins which play an essential function in cellular structure and activity. It prevents thè accumulation of fat in thè liver. Deficiency symptom is indicated by retarded growth and accumulation of fat in thè liver, especially in pigs and chicks. Choline is also concemed with thè prevention of perosis or slipped tendon in chicks. Vitamin B12 Another name so called by this vitamin is cyanocobalamin and it is thè most complex of all vitamins. In this lecture, you will not be bothered about its structure. The vitamin is believed to be synthesised exclusively by micro-organisms and its presence in foods is thought to be mainly of microbial origin. Vitamin B12 could be obtained from animai origin, thè liver being a principally rich source. The matured animals are less affected by thè deficiency of vitamin B12, unlike young growing animals in which there is retarded growth and high mortality. In poultry, poor feathenng and kidney destruction may take place. Despite thè fact that thè deficient birds remain healthy but hatchability is badly affected. In pigs, there is uncoordination of thè hind legs. Vitamin C Vitamin C is more popular among other vitamins. Chemically, it is otherwise called L-ascorbic acid and posses thè following simple formula: HO C I H - C ----- I H O - C - M I CHjOU Vitamin C is heat-stable in acid solution, decompose in alleali and thè destruction is motivated by exposure to light. The most common sources of thè vitamin are green leafy vegetables, citrus fruits and some other fruits. Deficiency scurvy occurs which is a disease in which multiple haemorrhages take place. Usually, there is weakness and especially at thè joints. There is pain, bleeding gums and loosening of thè teeth. Haemorrhages may also occur in thè conjuctivae, retina or even cerebrum. 6 7 UNIVERSITY OF IBADAN LIBRARY Summary Vitamins, which thè two main classes are fat soluble and water soluble are chemically unrelated organic compounds. The requirement by thè animate is very low but thè deficiency in these animate could result in poor growth, poor egg and milk production, loss of appetite high mortality and susceptibility to diseases. ». are vitamins? 2. Classify vitamins with specific examples. 3. What are thè functions and deficiency symptoms of vitamins A,D,E and K? References McDonald, P., R. A. Edwards and J.F.D. Green-halgh ( 1987). Animai Nutrition. ELBS edition of fourth edition. Maynard, L.A., Loosh J.K., Hintz H.F. and Warner R.G. (1979) Animai Nutrition. 7* Ed. New Delhi: Tata McGraw-Hill publishing company Ltd. Tillman A.D., Ridenour H.E and W.R. Getz ( 1986). A Guide to thè Feeding and Nutrition o f Ruminants in thè Tropics. Winrock International Institute for Agricultural Development. 68 UNIVERSITY OF IBADAN LIBRARY LECTURE ELEVEN The Nature, Properties and Classification of Enzymes Introduction Enzymes were discovered by thè German Chemist, Edward Buchner towards thè end of thè nineteenth century. The \fcord enzyme which literally means ‘in yeast’ serves as a collective name for thè many hundred of compounds that have been shown to have a catalytic action on specific biochemical reactions in living cells. Enzymes are molecules which catalyse biochemical reactions by acting on their substrates and converting them into products. Enzymes are referred to as reaction specific catalysts because, in contrast to inorganic (non protein) catalysts, each enzyme catalyses a small number of reactions, sometimes only one. Objectives 1. To understand thè nature and importance of enzymes in biochemcial reactions of living organisms. 2. To be able to name and classify enzymes according to thè type of reactions they catalyse. 3. To have a knowledge of thè properties of enzymes. Pre-Test 1. What are catalysts? 2. What is catalysis? 3. What are thè importance of enzymes? 4. Give four examples of enzymes of metabolic reactions. CONTENT • The importance of enzymes • The classification of enzymes • The properties of enzymes • C o-enzymcs 6 9 UNIVERSITY OF IBADAN LIBRARY The Importance of Enzymes Most biochemical reactions of living cells would occur very slowly were it not for catalysis by enzymes. Although, enzymes undergo physical change during biochemical reactions, they revert to their originai state after thè completion of reactions. Enzymes not only speed up reactions in thè living cells, they also control them, ensuring that metabolism proceeds in an orderly fashion. The Classification of Enzymes Generally, an enzyme is named by attaching thè suffix (-ase) to thè name of thè substrate on which it acts e.g. proteases act on proteins, maltose catalyses maltese and lipase acts on lipid. Enzymes are grouped according to thè type of reaction they catalyse. The groups are: 1. Transferases: Enzymes in this group play an importate part in energy production and other metabolic processes in cells. The reactions they participate in involve thè transfer of atoms or group of atoms from one molecule to another, e.g a hydrogen atom, phosphate group, amino group, aldehyde or kentone residues etc. Examples of enzymes classified under this group are phosphorylase, hexokinase, cholineacyttransferase etc. 2. Oxidoreductases: These include thè enzymes also known either as dehydrogenases (enzymes that specifically catalyse thè removai of hydrogen atom from a substrate e.g. alcohol dehydrogenase) or as oxidases (enzymes that catalyse thè addition of oxygen to hydrogen e.g. cytochrome oxidase) oxidoreductases are involved in thè final steps in respiration. 3. Hydrolases: These are enzymes catalysing hydrolysis of ester, ether, peptide, glycogyl etc. E.g. B-galactosidase, pepsin, Chymotrypsin etc. 4. Lyases: These are enzymes that catalyse thè removai of groups from substrate by mechanism different from hydrolysis. Examples are aldolase and fumarase. 5. Isomerases : These are enzymes catalysing thè transfer of atoms from one part of a molecule to another, e.g alanine racemase, triosephosphate isomerase. 6. Ligases: These include enzymes catalysing thè linking together oftwo 70 UNIVERSITY OF IBADAN LIBRARY compounds and thè breaking of a pyrophosphate bond in ATP (Adenosine triphosphate) or a similar compound e.g glutamine synthetase and succinic thiokinase. The Properties of Enzymes 1. Enzymes generally work very rapidly. This speed of action makes enzymes much more efficient than inorganic catalysts. 2. Enzymes are not destroyed by thè reactions they catalyse and so are reversible. However, they differ ffom inorganic catalysts in that they cannot be used indefinitely. Enzymes are very unstable and are readily inactivated by heat, acids etc. 3. Enzymes work in either directiòry' i.e forward and backward. Reactions catalysed by an enzyme will move in .these forward and backward direction until an equilibrium between substrate and product is reached. 4. Enzymes are inactivated by excessive heat. This is because they are proteins and at high temperatures, proteins are denatured. 5. Enzymes are sensitive to PH. Every enzyme has its own range of PH in which it functions most efficiently, but most enzymes in thè cells fìmction best at or a round neutral. 6. Enzymes are action specific. An enzymes will catalyse only one, or a type of reaction. Co-enzymes Many enzymes catalyse Chemical reactions only in thè presence of a specific non protein organic molecule called thè co-enzyme. In this type of reaction, it is only when both thè enzyme and thè co-enzyme are present, will catalysis occurs. Chemical reactions that require thè participation of co-enzymes are oxidoreductive, group transferring and isomerizative in nature. Also, reactions resulting in thè formation of covalent bonds require thè participation of co-enzymes. Chemical reactions including hydrolytic reactions catalysed by thè enzymes of thè digestive tract, are not known to require co-enzymes. An important co-enzyme is Nicotinamide Adenine Dinucleotide (NAD) which works in conjunctiori with dehydrogenase enzymes. 71 UNIVERSITY OF IBADAN LIBRARY Summary Enzymes are molecules which catalyse biochemcial reactions by acting on their Substrates and Converting them into products. The main function of enzymes is to speed up reactions in the living cells. They also control this reactions, ensuring that metabolism proceeds in an orderly fashion. An enzyme is named by attaching the suffix (-ase) to the name of the Substrate on which it acts. Enzymes are classified according to the type of reaction they catalyse. The groups are Transferases, Oxidoreductases, hydrolases, Iyases, Isomerases, and ligases. Some of the properties of enzymes are; their speed of action, limitation to their use in living cells, inactivation by excessive heat, sensitivity to PH, and reaction specificity. Many enzymes catalyse Chemical reactions only in the presence of specific non protein organic molecule called the co-enzyme. These reactions are oxidoreductive, group transfering and isomerizative in nature. Post-Test 1. What are the factors affecting the rate of enzyme catalysed reactions. 2. Classify enzymes according to their functions in biochemcial reactions in living cells. 3. What is a co-enzymes? References Chang, R. (1981). Physical Chemistry with Applications to Biological Systems; 2nd Ed. New York: Macmillan Publishing Co. Inc. Chesworth, J.M., Stuchbury, T. and Scaife, J.R. (1998). An Introduction to Agricultural Biochemistry. London: Chapman & Hall. Harper, H.A, Rodwell, V.W. and Mayes, P.A. (\919).-Review ofPhysiological Chemistry, 17* Ed. California: Lange Medical Publications, Löss Altos, Mensah, I.A., Asomaning, W.A., Bempah, O.A. and Yeboah, S.K. (1983). General and Physical Chemistry, 2nd Ed. Lagos: West African BookPublishers Ltd. Roberts, M.B.V. (1972). Biology: A Functional Approach; 2nd Ed. London:Cox and Wyman Ltd. 72 UNIVERSITY OF IBADAN LIBRARY LECTURE TWELVE Enzyme, It’s Mode of Action and Inhibition Introduction An enzyme-catalysed reaction is usually characterized by a very large increase in the rate (on the order of 106 to 1012). The enzyme molecule is capable of selectively catalysing certain reactants, called Substrates, while discriminating against other molecules. Enzymes generally work very rapidly and are not destroyed by the reactions they catalyse, and so are reversible. There are compounds in living cells that decrease the rate of an enzyme-catalysed reaction. These are known as inhibitors. Objectives 1. To have an insight on how enzymes work. 2. To understand the reason for the high degree of specificity shown by enzymes. 3. To have a knowledge of the importance of enzyme inhibition. Pre-Test 1. What do you understand by Chemical equilibrium? 2. What are the factors affecting the rate of Chemical reactions? 3. What do you understand by feed back mechanism? 4. Explain reversible and irreversible reactions. CONTENT • How enzymes work • Enzyme Inhibition How Enzymes Work When an enzyme-controlled reaction takes place, the enzyme and Substrate molecules combine with each other. The Substrate molecules collide with the usually much larger enzyme molecules and then combine with them. Figure 1 below shows an increase in the rate of reaction as presented by curve A with an increasing 73 UNIVERSITY OF IBADAN LIBRARY concentration o f substrate, thè enzym e concentration being kept Constant Fig. 1: The EJfect of Substrale Concentration on thè rate of an enzyme-controlled reaction The curve levels up at a point when thè substrate concentration reaches a certain level, and thè System has become saturated. This phenomenon indicates that, thè more substrate molecules there are, thè greater thè chances of substrate and enzyme molecules colliding in thè right way. Therefore thè only way to increase thè rate of reaction is to increase thè enzyme concentration to give a new picture as presented by curve B. In an enzyme controlled reaction, thè substrate molecules combine with thè enzyme to form an enzyme-substrate complex. The substrate molecules with their various bonds held in relation to each other by thè enzyme react together to form an enzyme-product complex, which then splits into thè enzyme and product. The enzyme, unchanged by thè reaction is re-usable. E + S ^ E S ^ P + E Where E and S are enzyme and substrate respectively; ES, an enzyme-substrate complex; and P, thè product formed. The high degree of specificity shown by enzymes leads to thè suggestion of thè lock and-key hypothesis, where thè substrate can be represented by thè padlock and enzyme by thè key. It is suggested that each enzyme molecule has a precise place 74 UNIVERSITY OF IBADAN LIBRARY on its surface, known as thè active site, to which thè substrate molecules become attached. The active site of an enzyme molecule has a distinctive configuration into which only certain specific substrate molecules will fit. The shape of this active site, and thè positions of thè different Chemical groups within it, ensure that only those substrate molecules with a complementary structure will. combine with thè enzyme (see Fig. 2). The lock-and-key hypothesis also explains why enzymes are inactivated by excessive heat. Since enzymes are proteins, denaturation by heat brings about changes in shape, and prevent thè substrate molecules fitting into thè Fig. 2: The lock-and-key hypothesis explaining enzyme action 75 UNIVERSITY OF IBADAN LIBRARY Enzyme Inhibition Inhibitors are compounds that decrease thè rate of an enzyme-catalysed reaction. The activity of certain enzymes may be regulated by a feedback mechanism so that thè end products act as specific inhibitors to thè enzymes in thè initial stages of a chain producing them. There are two types of enzyme inhibitions; reversible and irreversible. > Reversible Inhibition An equilibrium exists between thè enzyme and thè inhibitor. There are three important types: i) Competitive inhibition: A situation where both thè substrate (S) and thè inhibitor (I) compete for thè same active site. The reactions are E + S ^ E S — E + P E + 1 —EI Where thè complex EI does not form products. An increase in thè substrate concentration relative to thè inhibitor is required to overcome competitive inhibition. ii) Non competitive inhibition: A non competitive inhibitor usually does not bind at thè active site of thè enzyme. The reactions are: E +S —ES — P E + I - E I E + I ^ E S I Where both EI and ESI do not form products. Since I does not interfere with thè formation of ES, non competitive inhibition cannot be reversed by increasing thè substrate concentration. iii) Uncompetitive inhibition: Anuncompetitive inhibitor does not bind to thè enzyme, instead it binds reversibly to thè enzyme-substrate complex to yield an inactive ESI complex. The reactions are: 76 UNIVERSITY OF IBADAN LIBRARY E + S ^ E S — P ES + I ^ E S I where, thè ESI does not form a product. Again, since I does not interfere with thè formation of ES, uncompetitive inhibition cannot be reversed by increasing thè substrate concentration. Irreversible Inhibition In irreversible inhibition, inhibition progressively increases with thè passage of time. A complete inhibition is reached when thè concentration of thè irreversible inhibitor exceeds that of thè enzyme. A — B — U— ----- ►Z In this feed back mechanism, thè product Z inhibits thè enzyme involved in one of thè early steps and thereby limits thè amount of thè final products formed. Summary When an enzyme-catalysed reaction takes place, thè enzyme and substrate molecules combine with each other to form an enzyme-substrate complex which later transforms into an enzyme-product complex. This then splits into thè enzyme and product. The only way to increase thè rate of reaction is to increase thè enzyme concentration. The high degree of specificity shown by enzymes leads to thè suggestion of thè lock-and-key hypothesis, where thè substrate can be presented by thè padlock and enzyme by thè key. It is suggested that, an enzyme has an active site with a distinctive configuration into which only certain specific substrate molecules will fit. The activity of certain enzymes may be regulated by a feedback mechanism so that thè end products act as specific inhibitors to thè enzymes in thè initial stages of a chain producing them. Inhibitors are compounds that decrease thè rate of an enzyme-catalysed reactions. There are two main types, reversible and irreversible. There are three types of reversible inhibitors namely, competitive inhibition, non competitive inhibition and uncompetitive inhibition. 77 UNIVERSITY OF IBADAN LIBRARY Post-Tests 1. Describe an enzyme-catalysed reaction. 2. Explain thè concept of enzyme inhibition. 3. Describe with illustration, thè lock-and-key hypothesis. References Chang, R. ( 1981 ). Physical Chemistry with Applications to Biological Systems, 2™1 Ed. New York: Macmillan Pubiishing Co. Ine. Chesworth, J.M.; Stuchury, T. and Scaife, J.R. (1998). An Introduction to Agricultural Biochemistry. London: Chapman & Hall. Harper, H.A; Rodwell, V.W. and Mayes, P.A. (1979). Review ofPhysiological Chemistry, 17* Ed. California: Lange Medicai Publications, Los Altos. Roberts, M.B. V. ( 1972) Biology: A Functional Approach, 2nd Ed. London: Cox and lalyman Ltd. 78 UNIVERSITY OF IBADAN LIBRARY LECTURE THIRTEEN The Nature, Classification and Functions of Hormones Introduction Hormones are organic compounds produced in one part of thè body, from which they are transported to other parts where they produce a response. Hormones are secreted by endocrine organs directly into thè blood stream. They are carried by thè blood around thè body bringing responses in various organs referred to as target organs. Hormones have influence on one another and are integrated into a highly coordinated System called thè endocrine System. This System provides means o f communication within thè body o f an organism. The m essage transmitted from an endocrine organ to a target organ takes thè form o f a Chemical substance conveyed through thè blood System. Objectives 1. To understand thè nature and importance of hormones in thè physiological process of thè living organisms. 2. To have a knowledge of thè endocrine.system; thè glands and their secretions. 3. To understand thè functions-of hormones in thè animai body. Pre-Test 1. What are hormones? 2. What are thè importance of hormones? 3. Give examples of organs in thè body where hormones are produced. CONTENT • The endocrine System. • Hormones secreted by thè endocrine glands and their functions. 79 UNIVERSITY OF IBADAN LIBRARY The Endocrine System The endocrine System consists of glands widely separated from one another and having no direct anatomical relationship. The glands are commonly referred to as ductless glands because their secretions pass directly from their cells into thè blood stream, and not through a duct or a canal. The endocrine System consists of thè following glands; i) Pituitary gland ii) Thyroid gland iii) Parathyroid glands iv) Adrenal glands v) The Islets of Langerhans in thè pancreas vi) Pineal gland vii) Ovaries in thè female viii) Testes in thè male Hormones Secreted by thè Endocrine Glands and their Functions Pituitary giand The pituitary gland has three distinct parts; i) thè anterior lobe ii) thè middle lobe and iii) thè posterior lobe The anterior lobe: The hormones produced by thè anterior pituitary is responsive for thè stimulation of thè production hormones by other endocrine glands or thè growth of thè body as a whole. The hormones secreted by thè anterior lobe and their functions are: a) Growth hormone or som atotrophic hormone: stimulates growth directly and in association with other hormones. The hormone affects thè growth in thè length of thè long bones and promotes protein anabolism. It also influences thè absorption of calcium from from thè bowel and in conversion of glycogen to glucose. b) Thyrotrophic horm one or ThyroidStim ulating Horm one (TSH): Controls thè growth and activity of thè thyroid gland. It also influences thè uptake of iodine, for thè synthesis of thè hormone thyroxine and tri iodothyronine by thè thyroid gland. c) Adrenocorticotrophic H orm one (ACTH): stimulates thè adrenal gland to produce its hormones. 80 UNIVERSITY OF IBADAN LIBRARY d) Lactogenic Hormone (Prolactin): in conjunction with other hormones stimulates thè mammary glands to secrete milk. e) Gonado trophic Hormones (Sex hormones): The anterior lobe secretes three gonado trophic hormones; i) The Follicle Stimulating Hormone (FSH); which stimulates thè development and maturation of thè ovarian follicle in female animals and promotes thè production of spormatozoa (thè male germcells) in thè male. ii) The Luteinising Hormone (LH); promotes thè final maturation of thè ovarian follicle and influences thè discharge of mature ovum (ovulation). It is also responsible for thè formation of thè Corpus luteum (yellow body) which secretes an ovarian hormone known as progesterone. iii) The Interstitial Celi Stimulating Hormone (ICSH); stimulates thè interstitial cells in thè testes to secrete thè hormone testostorone. f) The Posterior Lobe: The secretion of thè posterior lobe is known as pituitrin and it consists of two hormones, oxytocin (pitocin) and vasopressin (Antidiuretic Hormone — ADH). i) Oxytocin: this hormone promotes contraction of thè uterine muscle and thè release of milk during lactation. ii) Vasopressin: increases thè permeability to water of thè cells in thè kidney and is responsible for thè contraction of thè involuntary muscle in thè walls of thè intestine, gali bladder, urinary bladder and blood vessels. g) The middle lobe: This is thè smallest part of thè pituitary gland. It is believed that it secretes a hormone that is associated with thè growth and development of melanocytes which give thè skin its colour. The Thyroid Gland The thyroid gland secretes three hormones; thyroxine, tri iodothyronine and calcitonin. The functions of thyroxine and tri iodothyronine are; i) The control of utilization of oxygen in thè body thus influencing basai metabolic rate. ii) Stimulation of thè absorption of carbohydrate from small intestine. iii) Influence of heat production during catabolism of nutrients materials in thè cells. iv) Association with nerve stability. v) Responsibility for thè maintenance of healthy skin and hair and vi) For normal mental and physical development. The function of calcitorum is to reduce thè blood level of calcium by inhibiting thè re-absorption of calcium from bones. 81 UNIVERSITY OF IBADAN LIBRARY The Parathyroid Glands The parathyroid glands secrete thè hormone parathormone, to maintain thè blood concentration of calcium within normal limits. The hormone stimulates thè mobilisation of calcium from thè bones. The Adrenal Glands The adrenal cortex produces a considerable number of different substances which have beenclassified into three groups; glucocorticoids, mineralocorticoids and sex hormones. Glucocorticoids: Contains cortisol and corticosterone for regulation of carbohydrate metabolism. Mineralocorticoids: Aldosterone is thè name given to thè main mineralocorticoid and its functions are associated with thè maintenance of thè electrolyte balance in thè body. The Sex Hormones: These are testosterone, oestrogen and progesterone. The adrenal gland is thè sources of sex hormones until thè testes and ovaries mature at puberty. The secretion of thè sex hormones by thè adrenal cortex is controlled y ACTH and not by gonado troping which stimulate thè testes and ovaries. The functions of thè sex hormones include; thè influence of development and maintenance of secondary characteristics in both male and female, and to increase thè deposition of protein in muscles and reduce thè excretion of nitrogen, especially in thè male. The adrenal medulla produces catecholamines called adrenalin and noradrenalin which function in; dilation of thè coronary arteries, thus increasing thè blood supply to thè heart muscle; dilation of thè bronchi, allowing greater amount of air to enter thè lungs at each inspiration; dilation of thè pupil of thè eye; constriction of blood vessels to thè skin, thus raising thè blood pressure and reducing thè secretion of saliva and other digestive juices. The Islets of Langerhans The Islets of Langerhans have two main types of celi. These are thè « cells which produce a hormone called glucagen and P cells which produce insulin. Both hormones influence thè level of glucose in blood, each balancing thè effects of thè other. Glucagen tends to raise thè blood glucose level while insulin reduces it. 82 UNIVERSITY OF IBADAN LIBRARY Functions of Glucagen 1. Raises blood glucose level. 2. Converts liver glycogen to glucose. 3. Promotes gluconeogenesis. Functions of Insulin 1. Reduc.es blood glucose level. 2. Enables glucose to enter cells. 3. Promotes conversion of glucose to glycogen. 4. Promotes Storage o f fat. 5. Promotes synthesis of protein. An insufficiency of insulin in thè body leads to thè development of a disease condition known as diabetes mellitus, whi,ch is characterised by disturbances in both glucose and fat metabolism. The Pineal Gland The functions of thè pineal gland are yet not clear. It may be associated with thè development of gonads by influencing thè release of gonado-trophic hormones ffom thè anterior pituitary. Ovaries in thè Female The hormones oestrogen and progesterone are produced in thè ovaries. The production of oestrogen is stimulated by thè gonado-trophin, Follicle Stimulating Hormone (FSH), where progesterone is produced ffom Corpus luteum under thè influence of thè Luteinising Hormone (LH). Functions of Oestrogen 1. Influences ovulation 2. Stimulates thè proliferation of thè endometrium in preparation for thè reception of fertilized ovum. Functions of Progesterone 1. Prepares thè endometrium to assist thè passage of spermatozoa. 2. Influences thè preparation of thè uterine walls for thè development of thè fertilized ovum or ova. 83 UNIVERSITY OF IBADAN LIBRARY Testes in thè Male The Luteinising Hormone, or as it is called in thè male, thè Interstitial Celi Stimulating Hormone from thè anterior lobe of thè pituitary gland stimulates thè testes to produce thè hormone testosterone. The function of testosterone is to influence thè development of thè body to sexual maturity. Summary Hormones are organic compounds produced in one part o f thè body, from which they are transported to other parts where thè produce a response. Hormones have influence on one another and are integrated into a highly cor-ordinated System called thè endocrine System. The endocrine System consists o f glands com m only referred to as ductless glands because their secretions pass directly from their cells into thè blood stream, and not through a duct. Hormones produced by thè anterior pituitary is responsible for the.stimulation o f thè production o f hormones by other endocrine glands or thè growth o f thè body as a whole. The thyroid gland, parathyroid glands, adrenal glands and thè Islet o f langerhans secrete hormones w hose main functions are to influence thè metabolic process. The hormones o f thè gonads i.e. thè ovaries in thè female and testes in thè male are associated with thè developm ent o f thè body to sexual maturity and thè reproductive process. Post-Tests 1. Describe thè endocrine System. 2. Give two examples of hormones that have direct influence on metabolism and in what ways? 3. Explain briefly thè functions of hormones produced by thè gonads. References Harper, H.A; Rodwell, V.W. and Mayes, P.A. (1979). Review ofPhysiological Chemistry, 17* Ed. California: Lange Medicai Publication, Loss Altos. Robets, M.B.V. ( 1972). Biology: A FunctionalApproach, 2nd Ed. London: Cox and Wyman Ltd. Ross, J.S. and Wilson, K.J.W. (1981). Foundations o fA natomy andPhysiology, 5* Ed. London: Churchill Livingstone. 84 UNIV SITY OF IBADAN LIBRARY LECTURE FOURTEEN Orgaiiisation and Control of Endocrine Systems Introduction At thè physiological level of organization in thè endocrine System, thè control units are cells. Hormones act to change thè activities of cells or thè number of responsible cells. The activity of thè entire endocrine System is a highly integrated network. Hence, a disturbance such as a removai or malfunction of one gland, leads to changes in thè fiinctions of many other glands and a change in thè activities of other hormones upon target cells (cells responsive to hormones). Objectives i) To have an insight into hormonal action. ii) Understanding thè mechanism of hormonal control. Pre-Test i) What is a negative feed-back mechanismf? ii) Describe thè following; a) hormonogen b) tropic hormones and c) target organs CONTENT • Hormone action. • Hormonal control mechanisms. Hormone Action The principle of endocrine action using thè thyroid gland as an example. 85 UNIVERSITY OF IBADAN LIBRARY Pituitary gland (anterior lobe) ◄.....J Thyroid stimulating hormone (Thyrotrophin) Inhibition (negative feed-back) Thyroid gland • Thyroxine Increased basa metabolic rate The thyroid gland secretes thyroxine which is a complex organic compound containing iodine. Thyroxine is responsible for controlling thè basai metabolic rate and is therefore important in growth regulation. The release of thyroxine into thè blood stream is triggered by a hormone secreted by thè anterior lobe of thè pituitary gland. This hormone is called thyroid stimulating hormone or thyrotrophic hormone. The production of this hormone is regulated by thyroxine itself. A slight excess in thè level of thyroxine in thè blood stream acts on thè pituitary to secrete less thyrotrophic hormone and this in tum reduces thè activity of thè thyroid gland leading to thè reduction in thè production of thyroxine. This reduction of thyroxine in thè blood stream removes thè inhibiting influence on thè pituitary so that more thyrotrophic hormone will be produced again. This example illustrates thè principles of hormone action and this is referred to as negative feed-back mechanism. Hormonal Control Mechanisms Various types of endocrine control systems have been recognized. Some of these are: 1. The sim plest appears to be a System in which thè hormone acts on specifìc cells, thereby promoting a change in thè controlled variable in thè extracellular 86 UNIVERSITY OF IBADAN LIBRARY fluid, which in tum regulates thè output of hormone by thè gland (fig. 1). This negative feed-back System can be changed by endocrine and neural action exerted either upon thè gland itself or upon thè hormonally responsive effector cells. Systems of this type appear to operate in thè case of insuline, parathyroid hormone (PTH) and aldosterone. An important feature of this type of System is thè absence of direct hypothalamic or pituitary control. F.g. 1: X Negative feed-back -(h), hormone EG, endocrine gland. X X and X 1, represents other factors operating independently of feed-back loop and influencing respectively, thè activity of EG and celi 2. A hormonogen (a hormone precursor) is secreted into thè blood stream by one organ, which is acted upon in thè blood by an enzyme from another organ and is converted to a tropic hormone, which stimulates thè production of a hormone by another organ. The hormone then acts on a target organ stimulating a response which leads to a decrease in enzyme production. E O -A , endocrine organ A EO - B, endocrine organ B An example is angiostensonogen (hormonogen) converted into angiostensin, then into aldosterone (hormone). 87 UNIVERSITY OF IBADAN LIBRARY 3. In this case, thè hormonal precursor hormonogen can be derived from thè diet or synthesized within thè organism. It goes through successive transformations in several additional organs before becoming a biologically active substance. An example is thè conversion of cholecalciferol to 25 - hydroxy - and 1, 25 - dyhydroxy cholecalciferol. Fig.3: 4. In this type of System, thè activity of thè endocrine gland is under thè control of thè hypothalamus. The control of secretion of growth hormone by thè anterior pituitary, and of vasoprelsin by thè posterior pituitary are examples. A differentiating feature of this type of System is that feed-back control is exerted not on thè endocrine gland directly, but upon hypothalamic function, which in tum regulates gland function. The feed-back effector appears to be one or more plasma constituents. 88 « UNIVERSITY OF IBADAN LIBRARY Post-Tests 1. Using thè thyroid gland as an example illustrate thè principle ofhormone action. 2. Describe two mechanisms of hormonal control. References J.S, Ross and K.J.W., Wilson (1981). Foundations ofA natom y an dP hysiology, 5th Ed. London: Churchill Livingstone. M.B.V. Roberts ( 1972). Biology: A Functional Approach. 2nd Ed. London: Cox and Wyman Ltd. Robert H Williams (1974). Test B ook o f E ndocrinology. 5* Ed. Philadelphia: W.B. Saunders Company. 89 UNIVERSITY OF IBADAN LIBRARY Studente are expected to send in questions, commente and evaluation on thè texts including any further help to tutors at locai leaming centres nearest to them. They may also write to us at thè University directing all enquiries to thè: Deputy Registrar Centra far Extemal Studies University of Ibadan, ìbadan. UNIVERSITY OF IBADAN LIBRARY