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Transcript
Biomolecules Biomolecules may be defined as the lifeless organic substances which form the basis of life and are responsible for the growth and maintenance of the living systems. Biomolecules essential for the life process are carbohydrates, proteins, lipids and nucleic acids. Carbohydrates are naturally occurring organic compounds of carbon, hydrogen and oxygen, distributed as Glucose, fructose, sucrose, starch, cellulose, etc. The ratio of hydrogen and oxygen as 2 : 1 and they can be represented by the general formula Cx(H2O)y where x and y are integers and may be the same or different. Glucose = Sucrose = Rhamnose = Deoxyribose = C6H12O6 C12H22O11 or C12(H2O)11 do not have hydrogen and oxygen in the ratio of 2 :1 and C6H12O5 C5H10O4 cannot be called as hydrates of carbon. In fact oxygen is present in the form of (-CHO), Keto (>C=0) or hydroxyl (-OH gp). Now carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones or large polymeric molecules which on hydrolysis yield polyhydroxy aldehydes and ketones. Classifications: (1) Monossaccharides: They are polyhydroxy aldehydes or ketones which cannot be decomposed further by hydrolysis to give simpler carbohydrates. G.F = (CH2O)n = 3 β 7 Glucose, fructose C6H12O6, galactose C6H12O6, ribose C6H10O5 etc (2) Oligosaccharides: They on hydrolysis give a definite number (2 β 10) molecules of monosaccaharides. They can be further divided into: Disaccharides: Carbohydrates which upon hydrolysis gives 2 units of the same or different monosaccharides. Sucrose Maltose Lactose - C12H22O11 C12H22O11 C12H22O11 Trisaccharides: They upon hydrolysis furnish 3 units of the same or different monosaccharides. e.g. Raffinose Glucose Fructose Galactose πΆ18 π»22 π16 + 2 π»2 π π»+ οΏ½β―β―β―οΏ½ πΆ6 π»12 π6 + πΆ6 π»12 π6 + πΆ6 π»12 π6 Tetrasaccharides: They upon hydrolysis give 4 units of the same or different monosaccharides. Glucose Fructose Galactose π»+ C24H42O21 + 3H2O οΏ½β―β―β―οΏ½ πΆ6 π»12 π6 + πΆ6 π»12 π6 + 2πΆ6 π»12 π6 Polysaccharides : They upon hydrolysis give a large number of monosaccharides. They have large molecular masses. Their General Formula = (C6H10O5)n where n = 100 β 3000 Example: Starch, Cellulose, glycogen, etc. Classification on the basis of taste: Sugars: Sweet to taste. Glucose, fructose Non-Sugars: Not sweet. Starch Reducing behaviours: Reducing Sugars: Carbohydrates which are capable of reducing Tollenβs and Fehlingβs e.g. Monosaccharides and disaccharides except sucrose. Non Reducing sugars: Carbohydrates which are unable to reduce Tollenβs reagent and Fehlingβs solution. E.g. Sucrose. Monosaccharides : Classification. Based on the nature of functional gp present. They are classified as Aldoses : Possessing an (-CHO) gp are termed as Aldoses. Ketones: possessing a C = O gp are called ketones. Their structural formulae: CHO (CHOH)n CH2OH n = 1,2,3,4, or 5 CH2OH C=O (CHOH)n CH2OH Kotoses n = 1,2,3 or 4 Open Chain: Hexoses β C6H12O6 Structure of D-Glucose HβC=O Ketohexose CH2OH H β C β OH C=O HO β C β H HO β C β H H β C β OH H β C β OH H β C β OH H β C β OH CH2OH CH2OH Cyclic form: The five membered ring structure contains 4 β carbon atoms and an oxygen atom and is called the furanose form. Resemblance with (C4H4O) Six membered ring structure contains five carbon atom and a pyranose form due to resemblance with C5H6O. Test for Glucose Glucose Decolourises Bromine water and the solution becomes colourless CHO (CHOH)4 CH2OH Fructose Does not decolourise the red colour of Br2 water No reaction π΅π.πππ‘ππ + (O)οΏ½β―β―β―β―β―οΏ½ COOH (CHOH)4 CH2OH D β gluconic acid Proteins Proteins are highly complex, nitrogenous organic compounds having very high molecular masses. They are polyamines form from alpha amino acids. Amino acids are the building units of proteins. They possess both an amino group and a carboxylic group. They are classified Fibrous and globular proteins. Based on the number of -NH2 and βCOOH group, amino acids that are present in protein can be classified into 3 categories. (1) Neutral - eg. Glycine, Valine, Alanine β equal number of NH2 and COOH group. (2) Acidic amino acid β 2 COOH groups and 1 NH2 group β eg. Asparatic acid, Glutamic acid (3) Basic amino acid β 2 NH2 and 1 COOH β eg Lysine, arginine, etc. Primary Structures of proteins: The primary structure of proteins refers to the sequence of amino acids held together by peptide linkages. Secondary structures of proteins: In a protein Peptide chains are arranged in a definite shape. The determination of this shape gives the secondary structure of proteins. Secondary Structures: The lone pair of electrons on the N-atom in the peptide bond is delocalized over the C=O group. As a result C-N bond acquires a partial double bond character. The amide part CO-NH is planar and rigid. Iso-electric point: An amino acid exists as a positive ion in acidic solution and as a negative ion in the basic solution. Therefore, on passing current, it will migrate towards the cathode in acidic solution and towards the anode in basic solution. Hence, at a particular pH of the solution, the amino acid molecule should not migrate to either electrode and should exist as a neutral dipolar ion. This pH is known as Isoelectric point. Denaturation of proteins: Proteins are very sensitive to the action of heat, acids, alkalis and electrolytes. When they are subjected to heat, acid and alkali they undergo coagulation to form fibrous proteins which are insoluble in water. This results in a change of physical and biological properties of protein. The coagulated protein thus obtained is called denatured protein and the process is called denaturation. Formation of zwitter ion: In aqueous solution the acidic carboxyl (-COOH) group loses a proton which is taken by the basic amino group. Zwitter ion is neutral but contains positive and negative charges. Due to the dipolar nature, it is also referred to as a dipolar ion. The amino acids exist in this form. They show amphoteric behaviour and react with both acids and bases. Enzymes: Enzymes are the important class of globular proteins which acts as a biocatalysts in the living species and are produced in the living cells. Eg. Invertase, Amylase, Maltose, Lactose. Mechanism: It follows a lock and key mechanism. It assumes the existence of active sites and cavities on the surface of the enzymatic molecules. I. Binding the enzyme (E) on the substrate (S) to form an enzyme β substrate complex. E + S β ES Enzyme β Substrate complex II. III. Products formation in the complex ES β EP Enzyme-Substrate complex Enzyme product Release of the product from the enzymes EP β Enzyme + Product Vitamins: Group of organic compounds which are required in very small amounts for the healthy growth and normal functioning of animal organisms. They are classified as: (1) Fat Soluble vitamins: Not readily soluble in water β e.g. Vitamin A, D, E and K (2) Water Soluble vitamins: e.g Vitamin B, B complex, Vitamin C Deficiency and their diseases Vitamin A Vitamin B Complex (a) Vitamin B1 (b) Vitamin B2 (c) Vitamin B3 (d) Vitamin B6 (e) Vitamin B12 Vitamin C Vitamin D Vitamin E Vitamin K Vitamin H Coenzyme Q10 - Night Blindness, Xerosis - Beri Beri Cheilosis, cracking of lips, inflammation of tongue Dermatitis ,graying of hairs and retardation of body and Mental health. Anaemia, Nervous disorders, Insomnia, Pellogra Anaemia, Inflammation of tongue and mouth - Scurvy, bleeding of gums, skin diseases Rickets, deformation of bones and teeth Sterility, Muscular atrophy Haemorrhage, Lengthening of the time of blood clotting Dermatitis, loss of hair and paralysis Low order of immunity of body against many diseases Nucleic Acid Nucleic Acids constitute an important class of biomolecules which are present in the nuclei of all living cells. They are biopolymers. The monomer present in them are called nucleotide. A nucleotide consists of three chemical constituents: a sugar, a nitrogen containing heterocyclic base and phosphate group. Composition and Primary Structure of Nucleic Acids: Nucleic acids are the polymers of nucleotides. Their composition and primary structures are described below: Constituents of Nucleic Acids A nucleotide consists of three chemical constituents: a sugar, a nitrogen containing heterocyclic base, and a phosphate group. (i) Sugars in nucleic acids: Two types of pentose sugars have been obtained by the hydrolysis of nucleic acids. They are π½ - D β ribose and π½- D β 2 deoxyribose. Their structures are as follows: (ii) In these sugars, the C1 is an anomeric carbon. Therefore, both the sugars can exist in πΌ and π½ β forms. The nucleotide present in DNA contains π½ -D-2 deoxyribose, whereas that present in RNA contains π½-D-ribose. Nitrogen bases in nucleic acids: The nitrogen base is a residue present in a nucleotide, is a heterocyclic nitrogenous base and is a derivative of either purine or pyrimidine. Thus, the nitrogen bases present in nucleic acids belong to either of the following two classes of heterocyclic nitrogenous bases. (a) Purines: The commonly found purines are adenine (abbreviated as A) and guanine (G). (b) Pyrimidines: The commonly found pyrimidines are thymine (T), cytosine (C) and uracil (U). The base residues present in RNA are adenine (A), guanine (G), cytosine (C) and uracil (U); while those present in DNA are adenine (A), guanine (G), cystosine (C) and thymine (T). (iii) Phosphate group: A nucleotide possesses a phosphoric acid unit. This unit is responsible for linking nucleotides together in a nucleic acid molecule. The phosphoric acid unit can be represented as given below: DNA : Deoxyribonucleic acid