Question

If there are 120 adenine molecules in B-DNA double helical structure showing 20 coils,what is pyrimidine nucleotides forming three hydrogen bonds in it-
A)80 B)100 C)120 D)140

Please explain.

Answer 1

B-DNA contains approximately 10 base pairs percoil, so 20 coils contain 200 base pairs. 120 adenine molecules correspond to
120 A-T base pairs. Number of G-C base pairs is 200-120=80.
Pyrimidine nucleotide forming 3 hydrogen bonds is cytidine monophosphate, so number of cytosine molecules is 80