A nucleotide is an organic molecule consisting of a heterocyclic nucleobase (a purine or a pyrimidine), a pentose sugar (deoxyribose in DNA or ribose in RNA), and a phosphate or polyphosphate group. (A nucleoside is similar, except that it contains only the sugar and base, without a phosphate.)

Nucleotide names are abbreviated into standard four-letter codes. The first letter is lower case and indicates whether the nucleotide in question is a ribonucleotide (r) or deoxyribonucleotide (d). The second letter indicates the nitrogenous base included (G,A,T,C,U). The third and fourth letters indicate the number of attached phosphates (Mono-, Di-, Tri-) and the presence of a phosphate (P). For example, deoxy-cytosine-triphosphate is abbreviated as dCTP.

Nucleotides are the monomers of nucleic acids and also play important roles in cellular energy transport and transformations (notably ATP and NAD+/NADH) and in enzyme regulation (see for example, protein kinase).

See also

• Nucleobase