mononucleotides

Mononucleotides are nucleotides that contain a single phosphate group. They consist of a nitrogenous base (adenine, cytosine, guanine, thymine, or uracil), a five‑carbon sugar (ribose in RNA or deoxyribose in DNA), and one phosphate group. When the sugar is ribose, the molecule is a ribonucleotide monophosphate (for example AMP, CMP, GMP, UMP); when the sugar is deoxyribose, it is a deoxyribonucleotide monophosphate (for example dAMP, dCMP, dGMP, dTMP).

Mononucleotides are often referred to as nucleoside monophosphates (NMPs). They are distinct from nucleosides, which lack the phosphate, and from dinucleotides or triphosphates, which contain two or three phosphate groups. The term mononucleotide can also be encountered in reference to various biological and biochemical contexts, including metabolism and signaling.

Biological roles and metabolism: Mononucleotides serve as precursors for nucleic acid synthesis, being phosphorylated to form the higher-energy diphosphate and triphosphate forms needed by polymerases. They can be produced de novo or via salvage pathways that recycle nucleobases. Kinases add phosphate groups to NMPs to yield NDPs and then NTPs, which are the true substrates for RNA and DNA synthesis in cells (RNA polymerases use NTPs; DNA polymerases use deoxynucleotide triphosphates).

Functional significance extends beyond nucleic acids. ATP and GTP function as major energy currencies and signaling molecules, while cyclic monophosphates such as cAMP and cGMP act as second messengers in many pathways. Mononucleotides also appear as components of cofactors and metabolic intermediates in various biosynthetic processes.