DNA (deoxyribonucleic acid) the genetic material of most living organisms, which is a major constituent of the chromosomes within the cell nucleus and plays a central role in the determination of hereditary characteristics by controlling protein synthesis in cells. It is also found in chloroplasts and mitochondria. DNA is a nucleic acid composed of two chains of nucleotides in which the sugar is deoxyribose and the bases are adenine , cytosine , guanine , and thymine (compare RNA ). DNA basically consists of a chemically linked sequence of subunits. Each subunit contains a nitrogenous base (a heterocyclic ring of carbon and nitrogen base), a pentose sugar (a five-carbon sugar in ring form), and a phosphate group. The nitrogenous bases fall into the two types; purine and pyrimidine. Pyrimidines have a six-member ring while purines have a fused- five and six –members ring. Each nucleic acid is has 4 basic types. The same two purines, adenine and guanine, are present in both DNA and RNA. The two pyrimidines in DNA are cytosine and thymine. The bases are usually referred to by their initial letters; so DNA contains A, G, C and T. DNA has 2 strands and these twin strands, in the form of a double helix. They are composed of successive units of the sugar de-oxyribose, phosphate and the bases adenine, cytosine, guanine and thymine, through which the twin strands are cross-linked: adenine to thymine and cytosine to guanine. In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner. (Micklos, D.A., and Freyer, G.A. 1990.)
The inspiration that genetic material is nucleic acid had its roots in the discovery of transformation by Griffith in1928......................
