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Multiple Choice
In the DNA double helix, how many hydrogen bonds form between cytosine and guanine?
A
One
B
Two
C
Three
D
Four
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1
Recall that in the DNA double helix, base pairing occurs between purines and pyrimidines following Chargaff's rules: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).
Understand that the stability of these base pairs is due to hydrogen bonds formed between the nitrogenous bases.
Know that adenine and thymine form two hydrogen bonds, which is why their pairing is slightly less stable compared to cytosine and guanine.
Recognize that cytosine and guanine form three hydrogen bonds, which contributes to the higher stability of C-G pairs in the DNA structure.
Therefore, the number of hydrogen bonds between cytosine and guanine is three.