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  4. If there are 120 adenine molecules in a B-DNA double helical structure showing 20 coils, what is the number of pyrimidine nucleotides forming three hydrogen bonds in it?

Q. If there are 120 adenine molecules in a B-DNA double helical structure showing 20 coils, what is the number of pyrimidine nucleotides forming three hydrogen bonds in it?

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Solution:

B-DNA shows 10 nucleotides per turn (coil) of helix, if there are 20 coils then total number of nucleotides is 200 out of which 120 are adenine (equal amount of thymine). So, the number of guanine (equal amount of cytosine) nucleotides is 80. Three hydrogen bonds are present between guanine and cytosine.