nucleostide

Nucleostide is not a standard term in biochemistry or molecular biology. It is likely a misspelling or miscommunication of nucleoside or nucleotide. This article focuses on nucleosides and their relationship to nucleotides, which are central to nucleic acid biology.

A nucleoside consists of a nitrogenous base attached to a five‑carbon sugar—ribose in RNA or deoxyribose in DNA—without any phosphate groups. The base is linked to the sugar via an N-glycosidic bond, typically at the N9 position for purines (adenine and guanine) and N1 for pyrimidines (cytosine, thymine, and uracil). When the sugar and base are combined with one or more phosphate groups, the molecule is a nucleotide.

Nucleosides are a subset of nucleotides, which are formed when a nucleoside is phosphorylated. In cells, kinases add phosphate groups to produce nucleoside monophosphates, diphosphates, and triphosphates. Nucleosides can also be generated or salvaged from nucleic acid turnover via specific enzymes, a process important for maintaining nucleotide pools for replication and transcription.

Biological roles of nucleosides include serving as the building blocks of nucleic acids (DNA and RNA) and acting as signaling molecules and energy carriers in certain contexts. Nucleoside analogs are widely used as antiviral and anticancer drugs because they interfere with nucleic acid synthesis or function. There is no widely accepted definition of a separate chemical class called “nucleostide”; if encountered, it most likely refers to nucleoside or to nucleotide-related concepts.