basparning

Basparning, or base pairing, is the hydrogen-bond–mediated pairing of nucleobases on opposing strands of nucleic acids (DNA or RNA) or within a single strand to form duplexes or secondary structures. In DNA, the canonical pairs are adenine with thymine (A–T) and cytosine with guanine (C–G). A–T forms two hydrogen bonds, and C–G forms three, contributing to the relative stability of GC-rich regions. In RNA, thymine is replaced by uracil, so adenine pairs with uracil (A–U) while C–G pairing remains three hydrogen bonds. Base pairing creates complementary templates that guide replication and transcription.

Base pairing underpins the double helix architecture of DNA and enables accurate genetic information transfer. Chargaff’s rules describe roughly equal amounts of A and T (or U in RNA) and of C and G in double-stranded contexts, reflecting their pairing relationships. Beyond replication and transcription, base pairing in RNA drives folding into secondary structures such as stems and hairpins, which are essential for the function of tRNA, rRNA, ribozymes, and regulatory RNAs.

Noncanonical base pairs also occur, including wobble pairs like G–U in RNA, which can influence structural dynamics and decoding. Mismatches and local context affect stability and fidelity, and cellular mechanisms such as proofreading and repair help maintain proper pairing. In laboratory settings, nucleic acid hybridization relies on base pairing to detect, quantify, or anneal complementary sequences, illustrating the practical importance of base pairing in biology and biotechnology.