Base pair

A base pair consists of two nucleobases joined by hydrogen bonds across complementary strands of a nucleic acid. Its pairing rules help stabilize the strands and encode sequence.

Watson–Crick base pairing: The canonical pairing of adenine with thymine or uracil, and guanine with cytosine, through complementary hydrogen-bond patterns. These recurring pairs form the standard rungs of DNA and RNA double helices.
Nucleobase: A nitrogen-containing molecule that forms part of nucleotides in DNA and RNA. Each member of a base pair is a nucleobase.
DNA replication: The cellular process that copies a DNA molecule before cell division. Each original strand guides synthesis of a complementary strand through base pairing.
Noncanonical base pair: A nucleobase pair whose geometry or hydrogen-bonding pattern differs from canonical Watson–Crick pairing. These pairs broaden the structural repertoire beyond standard complementary pairs.
Chargaff's rules: The empirical observations that DNA base composition varies among species and that adenine and thymine, and guanine and cytosine, occur in equal amounts in double-stranded DNA. Equal complementary-base amounts follow from pairing across DNA strands.
Hydrogen bond: An attraction involving a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom. Hydrogen bonds connect complementary bases across the two strands.
Nucleotide: A nucleic-acid building block composed of a nitrogenous base, a sugar, and one or more phosphate groups. A paired base is attached to the sugar-phosphate backbone as part of a nucleotide.
Polymerase chain reaction: A laboratory method that amplifies selected DNA sequences through repeated cycles of heating and enzymatic copying. Primer binding depends on complementary base pairing with target DNA.
Wobble base pair: A nonstandard pairing, especially between guanine and uracil, allowed at certain positions in RNA. Wobble pairing lets one transfer RNA recognize multiple codons.
Mutation: A heritable change in the nucleotide sequence of genetic material. A changed base can disrupt pairing or be copied as a new sequence variant.

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