Length of one turn of the helix in a β-form DNA is approximately
3.4 nm
2 nm
0.34 nm
20 nm
Correct answer: 3.4 nm
Solution
In β-form (B-form) DNA, there are about 10 base pairs per turn and each base pair contributes about 0.34 nm along the helix axis. Multiplying gives 3.4 nm for one complete turn.