In DNA, which base is complementary to cytosine?

In DNA, which base is complementary to cytosine? Guanine is complementary to cytosine. The two bases form a specific guanine–cytosine, or G–C, base pair in double-stranded DNA, held together by three hydrogen bonds.

This pairing is part of DNA’s complementary base-pairing rules: adenine pairs with thymine, and guanine pairs with cytosine. Because each base has a defined partner, the sequence of one DNA strand determines the sequence of the other. This makes it possible for cells to copy genetic information accurately during DNA replication.

Cytosine and guanine are both classified as nitrogenous bases, but they belong to different structural groups: cytosine is a pyrimidine, while guanine is a larger purine. A frequent mix-up comes from RNA, where adenine pairs with uracil instead of thymine. Cytosine still pairs with guanine in RNA, although this question specifically concerns DNA.