Talk about the DNA structure

Discovered by Watson and Crick, DNA are double helical polynucleotides wound around each other, and purines always face pyrimidines (A and T 2 H bonds C and G 3 H bonds) DNA has two complementary chains each strand has a backbone and nitrogenous bases. the strands are antiparallel helix is 2nm in diameter, turn is 3.4 nm in length and two successive nucleotides are 0.34 nm apart, they may be B helix (water rich), A helix (poor water) or Z helix (vitro) (named according to major and minor grooves)