Watson, Crick and Wilkins described the structure of DNA but also indicated how it could be replicated and transfer from one organism to its off spring. Salient features of double helix structure of DNA include :
• Double helix made of two polynucleotide chains.
• Sugar and phosphate form backbone and N-base project inside.
• The two chains are antiparallel with one chain has the polarity of 5′ → 3′, the other has 3’→ 5.
• Presence of double hydrogen bonds between A=T, and triple bond to between G = C The . purine always comes opposite to pyrimidines to create uniform distance.
• Two chains are coiled in a right handed fashion.
• Pitch (one turn) of helix is 3.4 nm (= 34 A) contains 10 bp with 0.34 nm (3.4 A) gap between adjacent bps. (1 nm = 10-9 m) • Two chains of DNA are 20 A far apart, due to the pairing of purines with pyrimidines. This distance remains constant.
• The plane of one base pair stacks over the other in double helix to confer stability
Rosalind Franklin confirmed this structure of DNA through X-Ray crystallography.
