Mononucleotide

A mononucleotide is a nucleotide that contains a nucleobase attached to a five‑carbon sugar (ribose in RNA or deoxyribose in DNA) and a single phosphate group. In common biochemical usage, mononucleotides are the monophosphate forms of nucleotides, often written as NMP, such as AMP, CMP, GMP, UMP, or, in the DNA context, dAMP, dCMP, dGMP, and dTMP.

Structure and types: Each mononucleotide features a nucleobase linked to the sugar via a β‑N‑glycosidic bond to the C1′ of the sugar, with a phosphate esterified to the 5′‑hydroxyl group. The sugar is ribose in RNA and deoxyribose in DNA. They are the basic building blocks of nucleic acids and can exist as ribonucleotides (adenylate, cytidylate, guanylate, uridylate) or deoxyribonucleotides (deoxyadenylate, deoxycytidylate, deoxyguanylate, deoxythymidylate).

Roles and significance: Mononucleotides serve as precursors for nucleic acid synthesis and participate in cellular metabolism after conversion to diphosphates and triphosphates. While ATP and GTP are famous triphosphates used for energy transfer, monophosphates are essential building blocks and can be interconverted by kinases and phosphatases. Cyclic mononucleotides, such as cyclic AMP and cyclic GMP, act as important second messengers in signal transduction pathways.

Occurrence and synthesis: They are produced by de novo nucleotide synthesis and by salvage pathways from nucleosides, and they are recycled during nucleic acid turnover. Phosphorylation state and sugar type determine whether a given mononucleotide participates in RNA, DNA, or signaling processes.