Question

If there are 135 hydrogen bonds between two strands of a fragment of DNA double helix, which contains 23 Guanine nitrogen bases. What is its total length?

• A. 19.04 A
• B. 190.4 A
• C. 1904 A
• D. 190.4 nm

Answer 1

Answer: (B)

If the hydrogen bonds between two strands of a fragment of DNA double helix is 135, then hydrogen bonds between guanine and cytosine is $\text{(}23\times 3\text{) }69$ (as, GC pairs with three hydrogen bonds). $\therefore$ The adenine nitrogen bases $=69-135=66÷2=33$ The total nitrogen bases = 56 Distance between one $bp=3,4\mathring{A}$ $\therefore$ Total length $=56\times 3.4=190.4\mathring{A}$