Purine base that bonds with cytosine.

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Multiple Choice

Purine base that bonds with cytosine.

Explanation:
Nucleic acid base pairing occurs between purines and pyrimidines to keep the helix width uniform. Among the purines, adenine and guanine, only guanine pairs with cytosine (which is a pyrimidine). That guanine-cytosine pairing forms three hydrogen bonds, giving GC regions extra stability compared with AT (or AU) pairs. In DNA, adenine pairs with thymine; in RNA, adenine pairs with uracil, while cytosine still pairs with guanine. So the purine that bonds with cytosine is guanine.

Nucleic acid base pairing occurs between purines and pyrimidines to keep the helix width uniform. Among the purines, adenine and guanine, only guanine pairs with cytosine (which is a pyrimidine). That guanine-cytosine pairing forms three hydrogen bonds, giving GC regions extra stability compared with AT (or AU) pairs. In DNA, adenine pairs with thymine; in RNA, adenine pairs with uracil, while cytosine still pairs with guanine. So the purine that bonds with cytosine is guanine.

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