Biomolecules

Carbohydrates Biomolecules are the complex organic molecules that form the basis of life and are responsible for growth and maintenance of all living organisms. They include carbohydrates, proteins, enzymes, vitamins, nucleic acids. Carbohydrates are the polyhydroxy aldehydes or polyhydroxy ketones. The carbohydrates can be classified on the basis of the hydrolysis product as monosaccharides (simplest carbohydrates), oligosaccharides and polysaccharides. They can also be classified on the basis of reducing properties as Reducing sugars and Non-reducing sugars. On the basis of taste, the carbohydrates can either be sugars (sweet taste) or non-sugars (not sweet in taste). Glucose is an aldohexose. There are two forms of glucose: -glucose and -glucose. In the aqueous solution, both the forms of glucose show mutarotation. Six membered cyclic structure for glucose is based on the structure of pyran known as the pyranose structure. Many attempts have been made to decide the cyclic structure of glucose. The important ones are Fischer Projection Formulae and the Haworth Projection Formulae. The - glucose and - glucose, differ only in the orientation of the hydroxyl group at C-1 atom. Such pairs are called Anomers. Fructose is a ketohexose, found in fruits and has furanose structure. Disaccharides are formed by the condensation reaction of two monosaccharide units. Monosaccharides are linked together by glycosidic linkages to form disaccharides and polysaccharides. Sucrose or cane sugar is an important disaccharide. The hydrolysis of sucrose involves a change in the optical activity of solution from dextrorotation to laevorotation; it is called the inversion of cane sugar. Starch is a polysaccharide of -glucose and can be separated into fractions: amylose (20%) and amylopectin (80%). Proteins Proteins are nitrogenous organic compounds (polyamides) of high molecular mass. Proteins are the condensation polymers of about 20 different -amino acids which are linked by peptide bonds. Amino acids are the compounds which contain an amino group and a carboxylic group. Essential amino acids cannot be synthesised in the human body and must be supplied through our diet whereas non-essential amino acids can be synthesised in human body and therefore, we do not require them in our diet. On the basis of relative number of amino and carboxylic groups, amino acids can be acidic, basic or neutral. In aqueous solution, amino acid molecule exits as a dipolar ion, called Zwitter ion. The pH at which there is no net migration of the amino acid under the influence of the applied electric field is the isoelectric point. Based on the molecular shape, proteins are classified as Fibrous proteins and Globular proteins. On the basis of hydrolysis product, proteins may be simple, conjugated and derived proteins. The structure of protein is studied at four different levels, i.e., primary, secondary, tertiary and quaternary structure. The sequence of the amino acids in a protein is said to be its primary structure. It is responsible for the specific biological functions of the protein. The arrangement of peptide chain into definite 3-D structures is called secondary structure of proteins. This arrangement is due to the folding of chain. The folding gives rise to two types of structures: a-helix and b-pleated sheets. The a-helix is due to the formation of hydrogen bonds between the amide groups of the same peptide chain. b-pleated sheets is formed when the chain of the a-amino acids are arranged side-by-side. Tertiary structure arises due to the further folding, coiling and bending of the secondary structure. Quaternary structure determines the number of sub-units and their arrangement in a protein molecule. The secondary and tertiary structures of proteins get disturbed on changing the pH or temperature as they are not able to perform their functions. This is known as denaturation of proteins. During denaturation, the protein molecule uncoils from an ordered and specific conformation into a more random conformation. Enzymes Enzymes are biological catalysts produced by the living cells which catalyze many biochemical reactions in animal and plant bodies. Chemically enzymes are naturally occurring simple or conjugate proteins. They speed up the biochemical reactions up to ten million times as compared to the uncatalysed reactions. Biochemical reactions occurring in the body of a living organism during life processes such as digestion, respiration, control and coordination, etc. are catalysed by enzymes. Mostly enzymes require an additional non-protein chemical component for their activity called a cofactor. Cofactor can be metal ions such as Fe2+, Mg2+, Mn2+ or Zn2+. A cofactor that is tightly or even covalently bound to the enzyme protein is called a prosthetic group. Enzymes are highly specific and can discriminate between very closely related molecules. The enzymes are active at moderate temperature (about 310 K) and pH (around 7). Only the active site of an enzyme combines with the substrate. Enzyme catalysis can be explained on the basis of lock and key mechanism. Vitamins A group of biomolecules which are not produced by the body but are required in very small quantities for normal metabolic activities and healthy growth of human beings and animals is called vitamins. On the basis of their solubility vitamins can be either water soluble (vitamin B and C) or fat-soluble (vitamin A, D, E and K). Deficiency of different vitamins leads to different diseases. Such as deficiency of vitamin A causes Night blindness and Xerophthalmia, deficiency of vitamin B1 causes Beri beri, deficiency of vitamin B2 causes Cheilosis, deficiency of vitamin B6 causes Convulsions, deficiency of vitamin B12 causes Pernicious anaemia, deficiency of vitamin C causes Scurvy, deficiency of vitamin D causes Rickets and Osteomalacia, deficiency of vitamin E causes increased fragility of RBCs and muscular weakness, deficiency of vitamin K increases the blood clotting time. Nucleic acids A nucleic acid is a macromolecule composed of chains of monomeric nucleotide. The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acid has three components: pentose sugar (ribose or deoxyribose), nitrogen containing heterocyclic base (purine or a pyrimidine base) and a phosphate group (present at C5 of the sugar unit). The repeating units in the nucleic acid chain are linked through the phosphate group. Nucleosides contain a pentose sugar and a nitrogeneous base. Depending upon the sugar present, there are two types of nucleosides: Ribonucleosides and Deoxyribonucleosides. Nucleotides contain a pentose sugar, a nitrogeneous base and a phosphate group. These are of two types: Ribonucleotide and Deoxyribonucleotide. Deoxyribonucleic acid (DNA) is the genetic material and is responsible for the heredity character of the cell. It is present in the nucleus of the cell. DNA contains a pentose sugar (2-deoxyribose), nitrogenous bases (Purine: adenine, guanine; Pyrimidine: thymine, cytosine) and a Phosphate group.DNA has a Double helix structure. DNA consists of two polynucleotide strands running in opposite directions. They are held together by specific hydrogen bonding between bases. A purine base of one strand is always paired with pyrimidine base of the other strand. The possible pairing in DNA is between G (guanine) and C (cytosine) and between A (adenine) and T (thymine). Ribonucleic acid (RNA) is found as a genetic material in some plants and animals. It is found in nucleolus, cytoplasm and on the membrane in ribosomes. Each ribonucleotide consists of a ribose sugar, a nitrogenous base and a phosphate group. RNA molecule is single stranded, except in certain viruses in which it is double stranded. Base pairing occurs between Adenine and Uracil and between Guanine and Cytosine. Three classes of RNA, Messenger RNA, Ribosomal RNA and Transfer RNA are found in living organisms which actually carry out the protein synthesis in the cell. Hormones Hormones are the organic substances that are secreted by the ductless glands called endocrine glands. Hormones are transported to the different organs of the body by blood. Chemically, hormones can be proteins, polypeptides, single amino acids and steroids. These are required in small quantities and are specific in their functions. The deficiency of hormones leads to a particular disease, which may be treated by the administration of that hormone. Based on structure the hormones are classified as steroid hormones and non-steroid hormones. Testosterone, oestrogen, progesterone, cortisone are examples of steroid hormones. Non steroid hormones include thyroxin, adrenaline, insulin, glucagon, oxytocin and vasopressin. Pituitary gland secretes growth hormones, Thyroid secretes thyroxin, Pancreas secretes insulin, Testes secrete testosterone while Ovaries secrete oestrogen hormone.

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