What is the pitch (axial length of one complete 360-degree helical turn) of standard B-DNA double helix?
Answer and explanation
Correct answer: C. 3.4 nanometers (34 Angstroms)
- Step 1: In Watson-Crick B-DNA, there are approximately 10 base pairs per helical turn. Step 2. With 0.34 nm between adjacent base pairs, the total pitch of one full turn is 3.4 nm (34 A). Answer: 3.4 nanometers (34 Angstroms). Why not the others: 0.34 nm is the distance between two adjacent base pairs; 2.0 nm is the helical diameter of B-DNA; 3.6 nm is for alpha-helix proteins.
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