What describes complementary base pairing in nucleic acids?

Complementary base pairing in nucleic acids refers to the specific pairing of nitrogenous bases that forms the structural units of DNA and RNA molecules. This process is crucial for the stability of the nucleic acid structure and for the accurate replication and transcription of genetic information.

In DNA, adenine specifically pairs with thymine, and cytosine pairs with guanine. This specific pairing occurs due to hydrogen bonding: adenine forms two hydrogen bonds with thymine, while cytosine forms three hydrogen bonds with guanine. This complementary nature ensures that the genetic information is accurately replicated during cell division and that RNA molecules are correctly synthesized from DNA templates.

In RNA, adenine pairs with uracil (replacing thymine) instead of thymine, but the strict pairing rule of adenine with its respective partner and cytosine with its partner remains intact. Thus, the correct characterization of base pairing in nucleic acids is that adenine pairs with thymine (or uracil in RNA) and cytosine pairs with guanine, which accurately describes the fundamental mechanism by which these molecules maintain genetic fidelity.