A single nucleotide consists of a base, a five-carbon sugar and a phosphate group, which consists of phosphorous and oxygen. The base consists of adenine, thymine, guanine or cytosine, while the sugar is either ribose or deoxyribose.
Nucleotides are organic molecules that make up the basic units of DNA and RNA molecules. Nucleotides carry energy within cells and are important in metabolism and cell signaling. The combination of a base and a sugar is a nucleoside. In biology, the term nucleotide most often refers to a nucleoside monophosphate. However, a nucleoside diphosphate or a nucleoside triphosphate may also be considered a nucleotide.