DNA (deoxyribonucleic acid) is a nucleic acid; it contains the genetic information necessary for RNA (ribonucleic acid) and protein biosynthesis .
DNA is made up of two double-stranded polynucleotide chains. Each nucleotide consists of a pentose, 2-deoxy-D-ribose, to which the nitrogenous base and a phosphate group are covalently linked (N-glycosidic and phosphoester respectively). The nucleotides, in turn, are held together by "bridging" chemical bonds between the pentose molecules (phosphodiesteric chemical bond) . The two polynucleotide chains, on the other hand, are joined by hydrogen bonds (H-bonds); they are established between the complementary heterocyclic base pairs: two H-bonds between adenine (A) and thymine (T) and three H-bonds between guanine (G) and cytosine (C) .
To characterize the DNA (or a segment thereof) is the sequence of heterocyclic bases along the polynucleotide chain.
It is basically the right-handed double helix proposed in 1953 by James D. Watson and Francis H. Crick (B-form) .