Ribonucleotides and deoxyribonucleotides (collectively called nucleotides) are the building blocks of the nucleic acids, RNA and DNA, respectively. Nucleotides are composed of a sugar, a phosphate, and a base (see below).

The composition of DNA differs from that of RNA in only two respects. First, DNA uses nucleotides containing the sugar deoxyribose. RNA's nucleotides contain the sugar ribose. Second, DNA uses the bases adenine, guanine, cytosine, and thymine. RNA uses the bases adenine, guanine, cytosine, and uracil

Nucleotides differ from nucleosides in that the latter do not contain phosphate, so we sometimes refer to nucleotides as nucleoside (mono,di, or tri)-phosphates. For example, adenosine diphosphate is a nucleotide (also called ADP) Deoxyribonucleotides (written with a 'd') differ from ribonucleotides in containing deoxyribose as the sugar moiety instead of ribose. In some naming schemes, deoxythymidine nucleotides are written without the 'd', but the 'd' convention will be used here.

The table below lists the most common nucleotides found in cells.

AMP	CMP	GMP	UMP
ADP	CDP	GDP	UDP
ATP	CTP	GTP	UTP
dAMP	dCMP	dGMP	dTMP
dADP	dCDP	dGDP	dTDP
dATP	dCTP	dGTP	dTTP
cAMP	dUMP	dUDP	dUTP