Question

Length of one coil of B-DNA helix is

• A. 0.34 nm
• B. 3.4 nm
• C. 10 nm
• D. 20 nm

Answer 1

Answer: (B)

3.4 nm

The B-DNA is arranged in a right-handed double helix; the helix is 20$\mathring{A}$ wider and the number of base pairs per helical turn is 10.5. The plane of the base pairs in B-DNA is tilted about 6 degrees with respect to the helix axis. One complete turn of the double helix is 3.4 nm long and each of which has 10.5 base pairs, the distance between two consecutive base pairs is 0.34 nm. Thus, the correct answer is B.