- published: 29 Oct 2011
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Nucleotides are molecules that, when joined, make up the individual structural units of the nucleic acids RNA and DNA. In addition, nucleotides participate in cellular signaling (cGMP and cAMP), and are incorporated into important cofactors of enzymatic reactions (coenzyme A, FAD, FMN, and NADP+).
Nucleotide derivatives such as the nucleoside triphosphates play central roles in metabolism, in which capacity they serve as sources of chemical energy (ATP and GTP).
A nucleotide is composed of a nucleobase (nitrogenous base), a five-carbon sugar (either ribose or 2-deoxyribose), and one phosphate group. Without the phosphate group, the nucleobase and sugar compose a nucleoside. A nucleotide can thus also be called a nucleoside monophosphate. The phosphate groups form bonds with either the 2, 3, or 5-carbon of the sugar, with the 5-carbon site most common. Cyclic nucleotides form when the phosphate group is bound to two of the sugar's hydroxyl groups. Nucleotides contain either a purine or a pyrimidine base. Ribonucleotides are nucleotides in which the sugar is ribose. Deoxyribonucleotides are nucleotides in which the sugar is deoxyribose.