Given that the period is 34 A and the diameter of DNA is 20A

Given that the period is 34 A and the diameter of DNA is 20A, what is the angle of the B-DNA helix?

Solution

The double-helix has a diameter of 20 Å. Each adjacent base on one strand of the double-helix is 3.4 Å apart. Every 10 base-pairs constitutes a 360° turn in the helix, and the length of the helix is determined by 34 Å per 10 base-pairs.

The alignment of the bases can indicate the global orientation of a DNA strand. For purine nucleotides (A and G) the most probable angle is approximately 88°, whereas for pyrimidine (C and T) that angle is approximately 105°.