Which bases in DNA form three hydrogen bonds when paired?

The bases in DNA that form three hydrogen bonds when paired are guanine and cytosine. This pairing is crucial for the stability and integrity of the DNA double helix structure. Guanine has one carbonyl and two amino groups that allow it to form three hydrogen bonds with cytosine, which contains one carbonyl and one amino group. The formation of these three hydrogen bonds contributes to a stronger interaction compared to the two hydrogen bonds formed between adenine and thymine.

This stability is significant in various biological processes, including DNA replication and transcription, where the integrity of the base pairing can influence the accuracy of genetic information transfer. The strong bonding between guanine and cytosine helps to maintain the structure of DNA under conditions that may induce denaturation.