DNA helix

Deoxyribonucleic acid (DNA) helix consists of two anti-parallel long poly nucleotide chains. These chains, or strands, are composed of four types of nucleotides and held together by hydrogen bonds between the nitrogen bases of nucleotides. The nucleotides are divided into two groups; purines of Adenine (A) and Guanine (G), and pyrimidines of Cytosine (C), Thymine (T).  According to the Watson-Crick model of DNA, guanine (G) and Cytosine (C) bind together with three hydrogen bonds, whereas adenine (A) and thymine (T) bind with two hydrogen bonds. The pairing between A and T and between G and C is said to be complementary. This principle explains how only four bases in DNA can code for the huge amount of information needed to make an organism. The DNA is then formed into a double helix structure.