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Chapter No. 2 Biochemistry It is a branch of biology, which deals with the study of chemical components and chemical processes in living organisms. Or The scientific study of chemical substances, process, and reactions, that occurs in living organism. Importance Of Biochemistry A basic knowledge of biochemistry is essential for understanding anatomy (physical structure of organism) and physiology (study of functioning of living things), because all of the living structures of an organism have Biochemical Organization. For example, Photosynthesis, Respiration, Digestion and Muscle Contraction can all be described in Biochemical terms. Chemistry Of Life All living organism are made up of chemical compounds, which are either organic or inorganic. The most important organic compounds in living organisms are carbohydrates, proteins, lipids and nucleic acids. The important inorganic compounds are water, carbon dioxide, acids, bases and salts. The biochemical compounds of a typical bacterial (prokaryotic) and animal (eukaryotic) cell are: Cellular Metabolism And Material Exchange Chemicals taken in from the environment Used to make chemicals of living matter New cellular materials Used for E. Need METABOLISM: (Gk; matabole = to throw differently, to Change) All the chemical reactions taking place within a cell are collectively called Metabolism Anabolism Reaction: (Gk; katabole=throwing up) Those reactions in which simpler substances are combined to form complex substances with the help of energy are called anabolic reactions. Catabolic Reaction: (Gk; Katabole = throwing down) A metabolic process in which energy is released through the conversion of complex molecules into simpler ones. Catabolism (Destructive metabolism) Pe pti de Bo nd C-O Clycosipic Linkage Anabolism (constructive metabolism) C Ce la llu r uc S tr e tur N Po of ten en tia l e rg so y u rc e H , O O r g anic , N, P, S Co m p oun ds Im m ed i en ate s erg ou y A rce TP of s ent lem ic e ns dro ahe Tetr in g Central position Bas C o v al en tB o nd LIFE’S MOLECULAR DIVERSITY & PROPERTIES OF CARBON Carbon is the fundamental element of organic compounds. Certain special properties give it the central position in the skeleton of life. It can react with many other elements forming covalent bonds. When it combines with four other atoms or radicals, the four bonds are arranged symmetrically in a tetrahedron. (Tetraedron=four sided, hedra=face, an object with four triangular sides) Tetrahedron is a very stable configuration; this property combined with tetravalency of carbon makes it a favourable element for synthesis of complicated cellular structures. CARBON BONDING BEHAVIOUR Carbon atom combines covalently, forming branched or unbranched chains or ring structures. Carbon combines with H, O, N, P and S, forming a variety of organic compounds. Carbon and Hydrogen (C-H bond) is the potential source of chemical energy for all cellular activities. C-O association is glycosidic linkage provides stability to the complex carbohydrate molecules. Carbon combines with nitrogen to from peptide bonds and produce proteins, which are important due to their diversity (variety) in structure and function. (Peptide bond= A chemical bond formed when the amino group of one amino acid condenses with the carboxyl group of another) IMPORTANCE OF ORGANIC COMPOUNDS Large organic molecules (macromolecules) such as cellulose, fats, proteins etc are insoluble in water hence they form cellular structures. Macromolecules act as storage for smaller molecules like glucose that is later on used as source of energy by the cell. Micro molecules, such as glucose, amino acids, fatty acids etc. are either function as pool of energy or subunits to build macromolecules. Certain other unstable molecules that are immediately broken down to release energy e.g. ATP. Such compounds are instant source of energy for cellular respiration. Biochemical reactions Almost all e.g. Hydrolysis of Most abundant reactions of macromolecules in all organisms cell occur in presence of water (65---89%) e.g. Human Tissues Medium of life 20% in bone cells 85% in brain cells Heat capacity Solvent properties Ionization of water Heat of Vaporization Protection LIFE SUPPORTING PROPERTIES OF WATER Water As Solvent Solvent = A substance that dissolves another material (solute). Water is an excellent solvent for polar substances. These include ionic substances like salts, whose charged particles (ions) dissociate (separate) in water. Some non-ionic substances like sugar and simple alcohols, which contain changed (polar) groups such as (- OH), are dispersed in water. Once a substance is in solution its molecules or ions can move about freely, thus making it more chemically reactive. It is because of this property of water that almost all reactions in cells occur in aqueous media. In cells all chemical reactions are catalysed by enzymes, which work in aqueous environment. Non-polar organic molecules, such as fats are insoluble in water and help to maintain membranes that make compartments in the cells. High Heat Capacity: The specific heat capacity of water is the amount of heat, measured in calories to raise the temperature of 1g water by “1C0 ” (i.e., 150c —160c). It is “1” for water. Due to high heat capacity water can absorb much of heat with out increase in its temperature. The most of energy supplied is used to break hydrogen bonds that result in relatively small rise in temperature. Benefits: (Water’s Temperature Stabilizing Effects) i) Biochemical reactions proceed at more constant rates and are less likely to be inhibited by extremes of temperature. ii) Water also provides a very constant external environment for many cells and organisms. High Heat of Vaporization: Water absorbs much heat as it changes form liquid to gas. Heat of vaporization is expressed as clones absorbed per gram vaporized. The specific heat of vaporization of water is 574 Kcal/ Kg, which plays an important role in the regulation of heat of produced by oxidation. The high heat of vaporization means that a large amount of heat can be lost with minimal loss of water from the body e.g evaporation of only 2ml out of 1liter of water, lower the temperature of the remaining 998 ml by 10c Sweating and Panting of mammals The grening of mouth of source reptiles in sunshin IONIZATION OF WATER The water molecules ionize to from H+ and OH- ions. Transpiring leaves H2O H+ + OHThis reaction is reversible but equilibrium to maintain. At 25 0 c the concentration of each of H+ and OH- ions in pure water is about 10-7 mol/litre. The H+ and OH- ions affect, and take part in many of the reactions that occur in cells. PROTECTION Water is affective lubricant that provides protection against damage resulting from fiction. For example, tear protect the surface of eye from the rubbing of eyelids. Water also forms a fluid cushion around organs (lungs, heart etc) that helps to protect them form trauma. PROTEIN PRIMARY STRUCTURE: The primary structure is the number sequence of amino acids held together by peptide bonds in a polypeptide chain. The sequence of amino acids of a protein dictates its biological function. In turn this sequence is strictly controlled by the sequence of bases in DNA. Substitution of just a single amino acid can cause a major alteration of the function of protein e.g sickle cell anaemia. Example: Insulin Discover = F. Sanger (1944-1954) No. of amino acids = 51 Chains = 02 SECONDARY STRUCTURE: The polypeptide chains is protein molecule usually do not lie flat. They usually coil into a helix or into some other regular configuration. - Helix - pleated sheet - Helix : It usually takes the form of an extended spiral spring. The structure is maintained by many hydrogen bands which are formed between adjacent Co and NH groups. The H atom of NH group of one amino acid is bonded to “O” atom of the Co - Helix makes group three amino acids away. X-ray diffraction analysis shows that one complete turn for every 3.6 amino acids. H N-H R-C-H C=O H-N H-C-R O=C N-H R-C-N C=O H-N N-C-R O=C N-H R-C-H C=O N-H Example: Keratin [entirely - helical and hence fibrous] It is structural protein of hair, wool, nails, Claus, beaks feathers and horns. Its hardness and stretch ability vary with degree of cross-linking by disulphide bridges between neighbouring chains. Theoretically all Co and NH groups can participate in H-bonding So -helix is a very stable structure. ß-PLEATED SHEET: This protein comprises a number of adjacent chains which are arranged in parallel fashion but running in opposite directions to each other. They are joined together by H-bonds formed between the C=O and NH groups of one chain and NH and C=O groups of adjacent chains. This is called ß-configuration and the whole structure is known as a ß-pleated sheet. O C O N N R4 O N C C C C R5 N N O R1 N O C N C N N R2 O N C C C C N N C N R3 O N R 1 R3 O N R1 C N C C C C N C C N O R2 N O R4 N C O TERTIARY STRUCTURE: Usually the polypeptide chain bends and folds extensively forming a precise, compact, globular shape. This is proteins tertiary conformation and is maintained by the interaction of three types of bonds i.e. Ionic Hydrogen Disulphide bonds as well as hydrophobic interactions The latter are quantitatively the most important and occur when protein folds so as to shield hydrophobic side groups from the aqueous surroundings, at the same time exposing hydrophilic side chains. C=O H-N Hydrogen bonds between aminoacids Hydrogen Bonds between side chains O-H O=C Disulphide bond formed by sulpher-containing amino acids S S Ionic bond between charged groups of polypeptide chains CO H3N+ Hydrophobic interaction of non-polar R-groups RO R QUATERNARY STRUCTURE: Many highly complex proteins consist of an aggregation of polypeptide chains held together by hydrophobic interactions and Hydrogen and ionic bonds. Their precise arrangement is the quaternary structure. Example: Haemoglobin [auocked out by Kendrew and perutz] It consists of for separate polypeptide chains of two type’s i.e two -chains contain 141 amino acids which each ß chain contains 146 amino acids. Structure Fibrous Type Fibrous Globulins Composition Alobabr Simple Function Conjugated Nature Function Secondary structure most Perform structural important (little or no tertiary functions in cells and structure) organisms e.g. Insoluble in water Collagen (tendons, Physically tough bone matrix) Long parallel polypeptide Myosin (in muscles) cahins cross-linked at Silk (spider, rubes) interuals forming long Keratin (hair, horn fibres or sheets. and feathers) Tertiary structure most important Polypeptide chains tightly folded to form spherical shape. Easily soluble to form a colloidal suspension. Globulins of blood serum (immunology) Form antibodies. Form enzymes Form hormones Important in protoplasm b/c they hold water and other substances and serve to maintain molecular organisation. LEVELS OF PROTEIN STRUCTURE Level of structure Primary Description Sequence of amino acids Secondary Alpha helix and ß-sheet Tertiary Folding and twisting Type of Bond Covalent (peptide) bond between amino acids Hydrogen bond between amino acids along the peptide chain Hydrogen, ionic and Quaternary Several polypeptides covalent (S – S) bonds, hydrophobic interactions between R groups. Hydrogen, ion bond between polypeptide chains. CARBOHYDRATES (Hydrated Carbons) SEVERAL FORMULAS: C x (H2o) y, where x is whole number from three to many thousands. DEFINITION: Chemically, carbohydrates are defined as polyhedron aldihydes or ketenes or complex substances which on hydrolysis yield plyhydroxy aldalydr or ketene subunits. OR Organic compounds deceived from carbon, hydrogen, and oxygen. They are important source of food and energy for humans and animals. EXAMPLES: i) Cellulose of wood, cotton and paper ii) Starch preset in cereals, root tubers iii) Cane sugar and milk sugar etc. SOURCES: The sources of carbohydrates are green plants. These are primary produces of photosynthesis. Other compounds of plants (i-e proteins, lipids etc) are produced from carbohydrates by various chemical changes. IMPORTANCE: Carbohydrates are of great significance because i) They play both structural and functional roles. ii) Simple carbohydrates are the main source of energy in cells. iii) Some carbohydrates are the main constituents of cell walls in plants and micro-organisms. CONJUGATED MOLECULES: (Conjugate Latin = to marry) Carbohydrates in cell combine with proteins and lipids and the resultant compounds (conjugates compounds) are called glycoprotein and glycolipids respectively. These molecules are much important because. i) Glycoproteins and clycolipids, have structural role in the extra cellular matrix of animals and bacterial cell wall. ii) Both of those conjugated molecules are components of biological membranes. CLASSIFICATION OF CARBOHYDRATES (Carbohydrates also called saccharides that is a Greek word “Sakcharon” meaning sugar) Sugars Monosaccharides Polysaccharides (many sugars) Oligosaccharides (Few Sugars) A. PHYSICAL PROPERTIES i) They are small i) molecules ii) They are sweet in taste. iii) They are readily soluble in water. ii) iv) They are crystalline in form. v) They are not hydrolyzed. iii) They are larger than monosaccharide but smaller than polysaccharides. They are also sweet but their sweetness is less than that of monosaccharide. They are less soluble iv) They are also crystalline v) They are hydrolyzed and on hydrolysis 2—10 monosaccharide are produces. i) They are macromolecules. ii) They are tasteless. iii) They are insoluble iv) They are non crystalline v) They are also hydrolyzed and on hydrolysis they yield simple sugars. B. SYNTHESIS They are simple sugars Made by joining 2---10 They are made by anonosacckocides joining many molecules of monosaccharide C. DIAORAMATIC REPRESENTATION OF STRUCTURE Glycosidic linkage D. GENERAL FORMULA (CH2O)n n=3—7 Usually C12H22O11 (2—10 monosaccharide) Cx (H2O) E. CHEMICAL PROPERTIES All are reducing sugars Some are reducing All polysaccharides are sugars and some are non-reducing non reducing In nature monosaccharide with 3 to 7 carbon atoms are found. They are called trios (3c), tetroses (4c), pentoses (5c), hexoses (6c) and heptoses (7c) FORMULA: Glucose is the most important hexose. It is present in free state in fruits like grapes, figs and dates. Our blood normally contains 0.08% glucose. In combined form it is present in disaccharides and polysaceliarides e.g. Glucose is naturally produced in green plants by photosynthesis. Light energy Chlorphyll 6CO2 + 12H2O 12O6 + 6O2 + 6H2O Energy is consumed in this process. This energy is provided by sunlight. 717.6 Kcal of solar energy is required for the synthesis of 10 grams of glucose. This energy is stored in glucose as chemical energy. During oxidation (respiration) of glucose this energy is released in the body of organisms and is used in different activities e.g. in animals it is used for: i) Growth and repair ii) Maintenance of body temperature. SIGNIFICANCE OF MONOSACCHARIDES TRIOSES: C3H6O3 for example cluceraldelyde, Dihydroxyacetone. They are intermediate sin respiration (glycolysis) and photosynthesis (dark reaction) TETROSES: C4H8O4 Rare in nature. They occur mainly in bacteria. PENTOSES: CyH10O5 e.g. ribose, ribulose. They are the integral part of nucleic acids i.e, ribose is a constituent of RNA and deoryribose of DNA. They are involved in the synthesis of some co-enynos e.g. NAD and NADP. They are involved in the synthesis of AMP, ADP and ATP. They play a role in biochemical reactions e.g. Ribulose bisphosphate is the CO2 acceptor is photosynthesis. HEXOSES: C6H12O6 e.g. glucose, fructose, galactose, manose. They are immediate source of energy e.g glucose in sugar They are used in the synthesis of oligosaccharides. They are used for the synthesis of polysaccharides. SIGNIFICANCE OF OLIGOSACCHARIDES Most commonly studied are: Glucose + glucose = maltose Glucose + galactose = lactose (milk sugar) Glucose + fructose = sucrose (cane sugar, most abundant in planty, commercial sugars are sugar cane and sugar beat) Disacchacide and polysaccharide synthesis formula IMPORTANCE OF POLYSACCHARIDES IMPORTANCE OF STARCH: It is found in fruits, vegetables, grains, seeds and tubers. It is main reserve food material in plants, available for animals. It gives many molecules of glucose on hydrolysis. STARCH TEST: Starch gives blue colour with iodine. TYPES: Amylase have unbranched chain of glucose. It is soluble in hot water. AMYLOPECTIN: It has branched chains. It is insoluble in hot or cold water. IMPORTANCE OF GLYCOGEN It is also called Animal Starch. It is chide storage compound of animals. It is found in liver and muscles. It is also found in all animal cells. It gives glucose on hydrolysis. TEST: It is insoluble in water It gives red colour with iodine IMPORTANCE OF CELLULOSE It is most abundant carbohydrate in nature. Cotton and paper are the pure forms of cellulose. It is the main component of cell walls of plants. It cannot be digested in human trail. However it plays a role in reabsorption and propulsion of faces in large intestine. It is digested in herbivores due to presence of micro-organisms (bacteria, yeasts, protozoa). These micro-organisms secret an enzyme called cellulose for its digestion. It yields glucose molecules on hydrolysis. TEST: It is insoluble in water. It gives no colour with iodine. i) Solubility ii) Iodine test Starch Genrally insoluble Blue colour Glycogen Insoluble Cellulose Insoluble Red colour No colour PROTEIN The word protein is derived from a Greek word proteios meaning “first place”. Every one of us has tens of thousands of different hinds of proteins each with unique structure suited fro its function. Proteins are important to the structure of cells and organisms and participate everything they do. Proteins are made of amino-acids. An amino-acid can be defined as a molecule containing an amino group (NH2), a carboxyl group (-COOH2), and a hydrogen atom, all bonded to a central carbon atom: R= may be a hydrogen atom as in glycine or CH3 as in alamine or any other group. So amino-acids mainly differ due to the type or nature of R group. About 170 types of amino-acids have been found to occur in cells and tissues. Of these about 25 are constituents of proteins. Most of the proteins are however made of 20 types of amino-acids. AMINO ACIDS CAN BE LINKED BY PEPTIDE BONDS Cells link amino acids together by dehydration synthesis. The linkage between the hydroxyl group (-OH) of carboxylic group of one amino acid releases H2O and C-N link to form a bond called Peptide Bond. The resultant compound gycylolanine has two amino acid subunits and is called a dipeptide. A dipeptide has an amino group at one end a carbonyl group at the other end of the molecule. So both reactive parts are again available for further peptide bonds to produce tripeptide, tetrapeptide and pentapeptides etc. leading to a polypeptide chains. Polypeptides range in length from a few monomers to 3000 thousand or even more in different proteins. For example insulin has 51 amino acids where as haemoglobin has 574. LIPIDS (Gr. Lipos = fats) The lipids heterogonous group of compounds related to fatty acids. They are insoluble in water but soluble in organic solvents such as ether, alcohol, chloroform and benzene. Lipids include fats, oils waxes, cholesterol and related compounds. ACYLGLYCEROLS (triglycerides or neutral lipids) Acylglycerols can be defied as Esters of fatty acids and alcohol (glycerol). ESTER: It is defined a chemical compound produced as a result of chemical reaction of an alcohol with an acid and a water molecule is released as shown below. C2H5OH + HOOCCH3 C2H5OCOCN3 + N2O Alcohol Acetic acid an ester GLYCEROL: A three carbon alcohol, each of whose carbon bears a hydroxyl group. Glycerol forms the back bone of a fat molecule. FATTY ACIDS: Long hydrocarbon chains ending in a carboxyl (-COOH) group. Three fatty acids are attached to the glycerol backbone in a fat molecule. PROPERTIES OF FATTY ACIDS 1. Fatty acids contain even number (4-30) of carbon atoms in straight chains attached with hydrogen and having an (-COOH) group. 2. They may be salutated with no double bonds or unsaturated with 1---- 6 double bonds. 3. In animals the fatty acids are straight chains while in plants these may be branched on signed. 4. Solubility of fatty acids in organic solvents increases with increase in number of carbon atoms e.g. palonitic and (cl6) is much more soluble an organic solvent than butyric acid. 5. Melting paint also increases with increase in number of carbon atoms. e.g. the melting point of potmicitic and is 63.10c and of butyric acids -80c. Formula from book FATS AND OILS Fats containing unsaturated fatty acids are usually liquid at room temperature and are said to be oils e.g. most of plant fats. Fats containing saturated fatty acids are sold at room temperature e.g animal fats. SPECIFIC GRAVITY OF FATS AND OILS Fats and oils are lighter than water and have a specific gravity of about 0.8. They are not crystalline but can be crystallized under specific conditions. Q; What is the drawback of a good with high fat contents? Ans. Higher fat contents of food causes. Slower movement of faces through the bowels. The bacteria present in food convert the undigested fats into came causing compounds. Also the cholesterol level rises that results in heart disorders. PHOSPHOLIPIDS Phospholipids are derivatives of phosphotidic acid, which are composed of glycerol + fatty acids + nitrogenous bases. Nitrogen Bases e.g. chorine, ethanolamine and saline OR A phospholipid has almost the same molecular structure as a cylglycerol. The only difference is that a phospholipid has one of its fatty acids replaced by a phosphate ion (Po4) and an R group. _______ R- Represents a nitrogen base. Phospholipids are widespread in bacteria, animal and plant cells and frequently associated with membranes. WAXES Waxes are mixtures of long chain alhanes (C25 = C35) and alcohols, ketenes and esters of long chain fatty acids. They are mainly used as water prefixing material by plants and animals e.g A. Additional protective layer on cuticle of epidermis of some plant organs eg. Leaves and fruits. Waxes are esters of fatty B. Skin, fur and feathers of animals acids with long chain C. Exoskeleton of insects D. Beeswax is a constituent of the honeyalcohols comb of bees. TEREMPOIDS Terpenoids are very large and important group of compounds which are made up of simple repeating units called isoperenoid units that contain C5 H8 atoms. These units by condensation in different ways, gives rise to compounds such as rubber, carotenoids, steroids, terpenes etc. NUCLEIC ACIDS (DNA and RNA) ISOLATION: Nucleic acids were first isolated in 1870 by F. Mieschoer from the nuclei of pus cells and states sperms of fish. REASON FOR NAMING: Nucleic acids are called “nucleic acid” because of their acidic nature. DEFINITION: Nucleic acids are complex substances. They are polymers of units called nucleotides. NUCLEOTIDE: A nucleotide is made up of three subunits: Nucleoside= Nitrogen bare+sugar Nucleotide = nitrogen +sugar+phosphorus i) 5- carbon sugar (monosaccharide) ii) A nitrogen base iii) A phosphoric acid TYPES: Nucleic acids are of two types i-e. DNA (deoxyribonucleic acids) and RNA (ribonucleic acids) OCCURRENCE: DNA occurs in chromosome, in the nuclei of cells and in much lesser amounts in mitochondria and chloroplasts. Whereas RNA is present in the nucleolus in the ribosomes, in the cytosol and in smaller amounts in other parts of cell. RNA DNA Phosphoric Sugar Nitrogen Phosphoric Sugar acid bases acid Deoxyribose Ribose Purines (larger) Pyrimidine (smaller) Purines Adenine Adenine (A) Nitrogen bases Pyrimidine Guanine Guanine (G) Cytosine (F-?) Thyonine (F-?) Cytosine (F-?) Diagrams= Formation of nucleotide -------- show? Formula of ATP List of nucleotides and nucleosides CHARGAFF’S RULES 1. The amounts of A, T, G and C in DNA varies form species to species. 2. In each species, the amount of A = T and the amount of G = C The percentage of A + G equal 50% And percentage of T + C equal 50% Uracil (F-?) FEATURES OF THE DNA MOLECULE Maurice Wilkins and Rosalind Franklin used the technique of X-ray diffraction to determinate the structure of DNA. At the same time Watson and Crick published the model of DNA in 1953 in the Journal Nature. They suggested that DNA molecule has following characteristics. i) DNA consists of two plynucleotide chains. ii) The two strands are coiled round each other in the form of a double helix. iii) The two strands run in opposite direction i-e Antiparallel, the 3/ end one being opposite to the 5/ end of the other. iv) The two strands are held together by hydrogen bonds thymine ( T ) and Guanine (A) is always paired with cytosine ( c ). v) There are two hydrogen bonds between A and T ( A = T) and three H-bonds between G and C (G = C). vi) Along the axis of the molecule the base pairs are 0.34 nm apart and a complete turn of the double helix comprise 3.4 nm or 10 base pairs. (3.4 nm = 34 Angstrom) 5/ Sugar + Phosphate 3/ 3.4nm (10 base pairs) 5/ 3/ THE AMOUNT OF DNA The amount of DNA is fixed for a particular species, as it depends upon the number of chromosomes. The amount of DNA in germ cells (sperms and oxa) is one half to that of somatic cells (cells of body). RNA (Ribonucleic Acid) RNA is a polymer (many parts) of rob nucleotides. The RNA molecules occur as single strand, which may be folded back on itself, to give double helical characteristics. There are also four nitrogenous bases in RNA i-e A, G, C and uracil U. SYTHESIS: RNA is synthesized by DNA in a process known as transcription. Messenger RNA (mRNA) Ribosomal RNA (rRNA) Transfer RNA (tRNA) MESSENGER RNA: As the name indicates it takes the genetic message (message from DNA) from the nucleus to the ribosomes to form particular proteins. This is a single-strand molecule formed on a single strand of DNA by a process known as Transcription. In the formation of RNA only one strand of DNA molecule is copied. Messenger RNA carries the genetic information from DNA to ribosomes, where aminoacids are arranged according to the information in mRNA to form specific protein molecule. This type of RNA consists of a single strand of Variable length. Its length depends upon the size of the gene as well as the protein for which it is taking the message. For example, for a protein molecule of 1,000 amino acids, mRNA will have the length of 3,000 nucleotides. PERCENTAGE: mRNA is about 3 to 4% of the total RNA in the cell. The smallest mRNA molecule is approximately 300 nucleotide units long TRANSFER RNA Each amino acid has its own tRNA molecule which transfer amino acids present in the ribosome. It acts as an intermediate molecule between the triplet code of mRNA and the amino acid sequence of the polypeptide chain (protein). TYPES OF tRNA: There are more than 20 different tRNA molcecules. PERCENTAGE: tRNA comprises about 10-20% of the cellular RNA. SIZE: It is the smallest of all RNAs, consisting a chain length of 75 to 90 nucleotides. RIBOSOMAL RNA Ribosomal RNA was the first RNA to be identified. It makes approximately 80% of the total RNA of the cell. It is synthesized by genes present on the DNA of several chromosomes found with in a region of the nucleolus known as the Nucleolus Organiser. It is found in the cytoplasm where it is associated with protein molecules which together form the cells organelles known as ribosomes (in ribosomes RNA is 40---50% protein = 50---60%) ribosomes are the sites for protein synthesis where mRNA and tRNA molecule interact to translate the information from genes into a specific protein. COMPARISON OF “DNA” AND “RNA” 1. 2. 3. 4. 5. 6. 7. DNA It contains pentose sugar known as deoxyribos (formula) The molecule contains the phosphoric acid molecule which connects various sugars with one another. The nitrogen bases are Adenine, Guanine, cytosine and thymine. Molecules have four nucleotides as deoryadenomice monophasphate, deoryguanosine Môn phosphate. The molecule contains a double strand helix structure in which many nucleotides remain arranged in pair, DNA is a genetic material. Occurs in chromosomes, nucleoplasm and mitochondria etc. 1. 2. 3. 4. 5. 6. 7. RNA It contains pentose sugar called the ribose (formula) The molecule contains the phosphoric acid molecule which connects various sugars with one another. The nitrogen bases are: Adenine, Guanine, cytosine and uracil. Molecules have four nucleotides as adenosine Môn phosphate, guamosine monophsphate and uridine monophosphat. The molecules consist of single chain of polynucleotides. RNA is a carrier of genetic informations and it plays very significant role in the mechanism of protein in synthesis. It mostly occurs in nucleolus, micleoplams and cytoplasm.