形成DNA、RNA单体以及编码遗传信息的化学结构，也就是组成碱基对的碱基包括A、G、T、C、U。严格地说，碱基对是一对相互匹配的碱基（即A：T，G：C，A：U相互作用）被氢键连接起来。然而，它常被用来衡量DNA和RNA的长度（尽管RNA是单链）。它还与核苷酸互换使用，尽管后者是由一个五碳糖、磷酸和一个碱基组成。

The chemical structures that form the units of DNA and RNA and that encode genetic information i.e. the bases that make up the base-pairs are A, G, T, C and U (see DNA). Strictly, a base pair is a pair of complementary bases (i.e. the A:T, G:C and A:U interactions) held together by hydrogen bonds. However, this term is used loosely as a measure of DNA and RNA length (although RNA is single-stranded). The term is also used interchangeably with “nucleotide” although the latter is composed of a five-carbon sugar joined to a phosphate group and one of the bases.