Question

The width of B-DNA is ______ and each turn of its helix has ______ nucleotides.

• A. 34 $\mathring{A}$; 11
• B. 20 $\mathring{A}$ ; 12
• C. 40 $\mathring{A}$ ; 8
• D. 20 $\mathring{A}$; 10

Answer 1

The correct option is D 20 $\mathring{A}$; 10

The Watson-Crick structure is the B form DNA, or B-DNA that is the most stable structure for a random-sequence DNA molecule under physiological conditions. The DNA is arranged in a right-handed double helix, but the helix is 20$\mathring{A}$ wider and the number of base pairs per helical turn is around 10.5. The plane of the base pairs in B-DNA is tilted about 6 degree with respect to the helix axis. Correct answer is D.