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Monophosphate is a term used in chemistry and biochemistry to describe a compound that contains a single phosphate group attached to another molecule. In practice, it is used for two related categories: phosphate monoesters, where the phosphate is bound to an organic molecule by a single ester linkage, and nucleotide monophosphates, where a nucleoside carries one phosphate group, typically at the 5′ position.

Structure and properties: The phosphate group in monophosphates is typically tetrahedral around the phosphorus atom. Depending on pH, the non-esterified oxygens can be protonated or deprotonated, giving the molecule a negative charge at physiological conditions. This charge contributes to high water solubility and influences interactions with enzymes and other biomolecules. In nucleotide monophosphates, the phosphate connects the sugar to the phosphate moiety inside the larger nucleotide architecture.

Biological role: Monophosphates are common in metabolism and nucleic acid biology. Nucleotide monophosphates such as AMP, CMP, GMP, and UMP are fundamental building blocks for RNA and DNA synthesis. They also function as metabolic intermediates in various pathways, and in many cases are phosphorylated further to form diphosphates and triphosphates by specific kinases. Sugar phosphates, like glucose-6-phosphate, serve as key intermediates linking carbohydrate metabolism to nucleotide and energy metabolism.

Examples and classification: Nucleotide monophosphates represent a well-known class within monophosphates. Organic phosphate monoesters are widespread across biology and chemistry, including signaling molecules and metabolic intermediates. The term monophosphate distinguishes these species from di- and triphosphate derivatives.