Basepair

A base pair is a unit consisting of two nucleotides on complementary strands of nucleic acids that form a stable pair through hydrogen bonding. In the canonical form of DNA, the base adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). In RNA, which commonly participates in duplexes and structures, adenine pairs with uracil (U) instead of thymine. Base pairing underlies the antiparallel, double-helix arrangement of DNA and the complementary folding patterns seen in RNA.

Base pairs contribute to the chemical stability and information storage of the genome. A–T base pairs typically form two hydrogen bonds, while C–G base pairs form three, making GC-rich regions more thermally stable. The concept of base pairs also serves as a unit of measurement for DNA length, with one base pair corresponding to roughly 0.34 nanometers of the DNA rise in B-form DNA. A kilobase pair (kbp) equals 1,000 base pairs.

Beyond structure, base pairing is central to biological processes such as DNA replication, transcription, and RNA processing. Fidelity relies on correct pairing between newly synthesized strands and templates, with cellular repair systems correcting mismatches. While standard Watson-Crick pairing describes the most common interactions, noncanonical pairings and mismatches can occur and are a focus of genetic variation and repair mechanisms.