Nucleic Acid Metabolism

Abstract

Nucleic acids are polymers of nucleotides. The latter are composed of a five-carbon sugar (d-ribose or d-deoxyribose) linked both to a nitrogen base (purine or pyrimidine) and a phosphate group (nucleosides are nucleotides without this phosphate group). The purine and pyrimidine nucleotides which occur most frequently in the nucleic acids of cells are illustrated in figure 6.1. In the un-polymerised state, they occur as nucleoside diphosphates (NDP) and triphosphates (NTP) as well as the monophosphate forms illustrated. In the polymerised state, the phosphate on the 5’-OH of the sugar is linked to the 3’-OH of the adjacent sugar residue so that nucleic acids consist of a backbone of alternating residues of sugar and phosphate with the bases projecting out from this. Two types of nucleic acid exist, deoxyribonucleic acid (DNA) which is a polymer of deoxyribonucleotides and ribonucleic acid (RNA) which is a polymer of ribonucleotides. Nucleic acid metabolism is concerned with the synthesis and breakdown of purine and pyrimidine nucleotides, their utilisation in DNA and RNA synthesis and the structure, localisation and function of these nucleic acids.