Nucleoside

Definition

A glycosylamine composed of a nitrogenous base (purine or pyrimidine) covalently linked to a five-carbon sugar (ribose or deoxyribose) via a glycosidic bond; the structural precursor to nucleotides, lacking the phosphate group(s) that distinguish nucleotides. In arthropod biochemistry, nucleosides serve as metabolic intermediates, signaling molecules, and components of nucleic acid synthesis; they also represent the molecular target or metabolic product of several insecticidal and antiviral compounds.

Etymology

From nucleo- (nucleus, referring to the nuclear material) + -side (glycoside, indicating the sugar-base linkage)

Example

The nucleoside adenosine accumulates in the hemolymph of diapausing insects and functions as a metabolic regulator; synthetic nucleoside analogs such as acyclovir nucleosides are explored for controlling honey bee viruses by interfering with viral RNA polymerase.

Related Terms

• Nucleotide
• purine
• pyrimidine
• ribose
• deoxyribose
• DNA
• RNA
• glycosidic bond
• nucleobase
• adenosine
• guanosine
• cytidine
• thymidine
• uridine

Usage Notes

Distinguished from nucleotide by the absence of phosphate; nucleosides become nucleotides upon phosphorylation. In entomological toxicology, 'nucleoside' often appears in discussions of antiviral therapies for managed pollinators and of insect growth regulators that disrupt nucleic acid metabolism. Some nucleosides function as neuroactive compounds in arthropods (e.g., adenosine modulation of neural signaling in insects). The term is chemically precise and should not be used loosely for intact nucleic acids or for free bases without sugar moieties.