Which base always pairs with guanine in DNA?

In DNA, guanine forms a complementary base pair with cytosine. This pairing is crucial for maintaining the structure of the DNA double helix and ensuring accurate replication and transcription. The specific pairing occurs via the formation of three hydrogen bonds between the guanine and cytosine bases, which stabilizes the DNA molecule.

Adenine pairs with thymine in DNA, forming two hydrogen bonds. Uracil is found in RNA, where it replaces thymine and pairs with adenine. Understanding these base pair relationships is fundamental in molecular biology, as they underpin the processes of genetic encoding, replication, and expression in living organisms.