Question

B-DNA double helix makes a complete turn with

• A. Every 10 base pairs
• B. Every 20 base pairs
• C. Every 36 base pairs
• D. Every 3-6 base pairs

Answer 1

The correct option is A Every 10 base pairs

Watson and Crick proposed two strands of DNA - each in a right hand helix wound around the same axis. The two strands are held together by H-bonding between the bases. The diameter of B-DNA is 20$\mathring{A}$ and there are about 10 bases per helical turn (36${}^o$ of twist along the helix for each base pair). The major groove is wide, while the minor groove is narrow. Owing to the location of the helical axis in the centre of the base pairs, the edges of the base pairs are about equally deep in the interior.