nucleotide

1. (biochemistry) The monomer constituting DNA or RNA biopolymer molecules. Each nucleotide consists of a nitrogenous heterocyclic base (or nucleobase), which can be either a double-ringed purine or a single-ringed pyrimidine; a five-carbon pentose sugar (deoxyribose in DNA or ribose in RNA); and a phosphate group.Examples: "With a genome of only 400 million or so nucleotide bases, the pufferfish, Fugu rubripes rubripes, has the smallest known genome of any vertebrate animal. […] But the region of DNA between the landmarks can be a million or more nucleotides long."; "Magid draws […] a diagram depicting a restriction enzyme cutting neatly through a sequence of nucleotides."