One turn of the helix in a B- from DNA is approximately

Options

A. 0.34 nm
B. 3.4 nm
C. 2 nm
D. 20 nm

Answer

B

Explanation

B-DNA is helical structure with 20 `Å` diameter and the distance between the two base pairs is 3.4 `Å` and there are 10 base pairs in each turn or pitch (one round). Hence, one turn of the helix is approximately 34 `Å` or 3.4 nm (10 `Å` = 1.0 nm). Z-DNA (in comparision to B-DNA) is left handed double helical structure in which double helix winds to left in zig-zag pattern (instead of right like B-DNA).