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Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter Contents All living organisms are made up of the same chemicals i.e., elements and compounds. If we analyse a plant tissue, animal tissue or a microbial paste, we obtain elements like carbon, hydrogen, oxygen etc. HOW TO ANALYSE CHEMICAL COMPOSITION? While performing a chemical analysis, when a living tissue is grinded in trichloroacetic acid (Cl3CCOOH), a thick slurry is formed. This slurry when strained through cheese cloth or cotton gives two fractions, one is the filtrate which is called acid-soluble pool where thousands of organic compounds are found. The other fraction is called the retentate or the acid-insoluble pool where compounds like proteins, nucleic acids, polysaccharides etc. are found. All the carbon compounds that we get from living tissues can be called ‘biomolecules’. However, inorganic elements and compounds are also present in the living organisms, which can be identified with the help of a technique called ‘ash’ analysis. A small amount of a living tissue (say a leaf or liver) is weighed (wet weight) and dried. All the water evaporates. The remaining material gives dry weight. When this tissue is fully burnt, the carbon compounds are oxidised to gaseous forms like CO2 and water vapour that are lost and the remnant is called ‘ash’. This ash contains many inorganic elements like calcium, magnesium etc. In the acid-soluble fraction, inorganic compounds like sulphate, phosphate etc. are also present. Chapter 2 Biomolecules How to Analyse Chemical Composition? Primary and Secondary Metabolites Carbohydrates Amino Acids Proteins Lipids Nucleic Acids Dynamic State of Body Constituents – Concept of Metabolism The Living State Enzymes
32 Biomolecules NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 The most abundant element in cell/living matter is oxygen. Table : A comparison of elements present in non-living and living matter* Hydrogen (H) Carbon (C) Oxygen (O) Nitrogen (N) Sulphur (S) Sodium (Na) Calcium (Ca) Magnesium (Mg) Silicon (Si) Element 0.14 0.03 46.6 Very little 0.03 2.8 3.6 2.1 27.7 % Weight of Earth’s crust Human body 0.5 18.5 65.0 3.3 0.3 0.2 1.5 0.1 Negligible * Adapted from CNR Rao, , Universities Press, Hyderabad. Understanding Chemistry Fe++ and Cu++ are found in cytochromes. The concentration of the cations inside the cell is K > Na > Ca. Table : A list of inorganic constituents of living tissues Sodium Potassium Calcium Magnesium Water Compounds Component Na K Ca Mg H O NaCl, CaCO , PO , SO + 3– 2– 2 3 4 4 + ++ ++ Formula From a biological point of view we can classify the biomolecules into micromolecules and macromolecules. Biomolecules Micromolecules (acid soluble fraction) Macromolecules (acid insoluble fraction) Amino acids Simple sugars Nucleotides Polysaccharides Proteins Nucleic acid The acid soluble pool contain chemicals with small molecular mass of 18 - 800 daltons approximately. They are called micromolecules or biomicromolecules. They include amino acids, sugar, nucleotides etc. while those which are found in the acid insoluble fraction are called macromolecules or biomacromolecules. Lipids are not strictly macromolecules. Their molecular weight does not exceed 800 Da, but they are obtained in the acid insoluble fraction because when we grind a tissue, cell membrane and other membranes are broken into pieces and form vesicles which are not water soluble (lipids are also present in structures like cell membrane and other membranes). Therefore, these membrane fragments in the form of vesicles get separated along with the acid insoluble pool.
NEET Biomolecules 33 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 The acid-soluble fraction represents roughly the cytoplasmic composition (without organelles), while the acid- insoluble fraction represents the macromolecules of the cytoplasm and cell organelles. The two fractions together represent the entire chemical composition of living tissues or organisms. Table : Average composition of cells Water Proteins Carbohydrates Lipids Nucleic acids Ions Component % of the total cellular mass 70-90 10-15 3 2 5-7 1 Note: Water is the most abundant chemical in living organisms. PRIMARY AND SECONDARY METABOLITES Living organisms produce thousands of organic compounds (biomolecules) including amino acids, sugars, chlorophyll, haem etc. These are required for their basic or primary metabolic processes like photosynthesis, respiration, protein and lipid metabolism etc. These organic compounds are called primary metabolites. Primary metabolites have identifiable functions and play known roles in normal physiological processes. Many plants, fungi and microbes of certain genera and families synthesize a number of organic compounds (biomolecules) which are not involved in primary metabolism and seem to have no direct function in growth and development of organisms. Such compounds are called secondary metabolites. The functions or role of secondary metabolites in host organisms are not understood. However, many of them are useful to human welfare (e.g., rubber, drugs, spices, scents and pigments). Some secondary metabolites have ecological importance. Table : Some secondary metabolites Pigments Alkaloids Terpenoides Essential oils Toxins Lectins Drugs Polymeric substances Carotenoids, Anthocyanins, etc. Morphine, Codeine, etc. Monoterpenes, Diterpenes etc. Lemon grass oil, etc. Abrin, Ricin Concanavalin A Vinblastin, Curcumin, etc. Rubber, Gums, Cellulose CARBOHYDRATES Carbohydrates are mainly compounds of carbon, hydrogen and oxygen. These are also known as saccharides because their basic components are sugars. They are of two types: small and large (complex). Small carbohydrates (biomicromolecules) are further divided into monosaccharides, derived monosaccharides and oligosaccharides. Large carbohydrates (biomacromolecules) are called polysaccharides. 1. Monosaccharides : They are those sugars or simple carbohydrates which cannot be hydrolysed further into smaller components. These are composed of 3-7 carbon atoms and are biomicromolecules.
34 Biomolecules NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph.011-47623456 Example - Ribose, glucose, fructose etc. O CH OH 2 HO OH OH OH C H O (Glucose) 6 12 6 O HOCH2 OH OH OH C H O (Ribose) 5 10 5 H — C = O H — C — OH HO — C — H H — C — OH H — C — OH C — OH H H Open chain of Glucose H — C = O H — C — OH H — C — OH C — OH H H Open chain of Ribose H — C — OH Glucose, fructose, mannose, galactose are hexoses. These are white, sweet–tasting, crystalline and extremely, soluble in water. Glucose is the universal sugar. It is also known as dextrose or grape sugar or corn sugar. Fructose is called fruit sugar. It is also known as levulose. It is the sweetest among naturally occurring sugars. Monosaccharides have ‘free’ aldehyde or ketone group which can reduce Cu++ to Cu+ . Hence, these are also called reducing sugars. 2. Derived monosaccharides : Monosaccharides are modified variously to form a number of different substances. Deoxy sugar : e.g. Deoxygenation (removal of oxygen at 2nd carbon) of ribose produces deoxyribose, a constituent of DNA. O HC H 2 O OH OH Ribose (C )5 H 3 H 2 1 H OH H 5 4 Deoxygenation O HC H 2 O HO H Deoxyribose (C )5 H 3 H 2 1 H OH H 5 4 Amino sugar : e.g. glucosamine Sugar acid : e.g. glucuronic acid, ascorbic acid Sugar alcohol : e.g. mannitol (present in brown algae) 3. Oligosaccharides : They are small carbohydrates which are formed by condensation of 2-9 monosaccharides. The monosaccharide units are joined together by glycosidic bond, formed by dehydration. It is normally formed between carbon atoms 1 and 4 of neighbouring unit (1, 4 bond). Depending upon the number of monosaccharide molecules condensed to form oligosaccharides, they can be disaccharides (e.g., sucrose, maltose, lactose, trehalose (present in haemolymph of insects), trisaccharides (e.g., raffinose - made up of glucose, fructose and galactose), tetrasaccharides (e.g., stachyose) etc. O CH OH 2 OH OH Glucose H H H H OH O O CH OH 2 OH OH H H H H OH H H Glycosidic bond 1-4 Maltose Glucose 6 5 4 3 2 1 6 5 4 3 2 1