What term describes the perfect fit between nucleotides, such as A with T and C with G?

• A. Base pairing
• B. Complementarity
• C. Antiparallelism
• D. Hydrogen bonding

Answer: (A)

Base pairing is the idea that specific nucleotides pair across the two DNA strands, so adenine matches with thymine and cytosine matches with guanine. This pairing is not arbitrary—the shapes of the bases and the ability to form specific hydrogen bonds make these pairs fit together like puzzle pieces, which helps keep the DNA double helix with a uniform width. A-T pairs form two hydrogen bonds, and C-G pairs form three, providing both stability and fidelity during processes like replication and transcription.

Hydrogen bonding explains the mechanism behind the pairing, while antiparallelism describes the orientation of the two strands, and complementarity refers to the usable matching relationship between one strand and its partner. But the term that captures the precise, rule-based fit between bases is base pairing.