Biomolecules — Class 12 Chemistry

Biomolecules are the complex organic molecules that build and run living systems: carbohydrates, proteins, nucleic acids and lipids, along with vitamins and hormones. Carbohydrates are optically active polyhydroxy aldehydes or ketones, or compounds that yield these on hydrolysis; they are classed as monosaccharides (glucose, fructose), oligosaccharides such as disaccharides (sucrose, maltose, lactose) and polysaccharides (starch, cellulose, glycogen). Glucose, an aldohexose, exists in open-chain and cyclic hemiacetal (pyranose) forms whose anomers differ at the anomeric carbon. Proteins are polymers of about twenty alpha-amino acids joined by peptide bonds; ten are essential and must come from the diet. Proteins have primary, secondary (alpha-helix and beta-pleated sheet), tertiary and quaternary structures, and lose biological activity on denaturation when these higher structures are disrupted. Enzymes are highly specific protein biocatalysts that lower activation energy. Vitamins are essential dietary factors classed as fat soluble (A, D, E, K) or water soluble (B group and C), and their deficiency causes specific diseases. Nucleic acids, DNA and RNA, are polymers of nucleotides made of a base, a pentose sugar and a phosphate; DNA stores genetic information as a double helix while RNA carries out protein synthesis. Hormones act as chemical messengers regulating body functions.