ribonucleoside

Ribonucleoside is a type of nucleoside in which a nitrogenous base is covalently attached to a ribose sugar. In ribonucleosides, the sugar is the five-carbon D-ribose, and the glycosidic bond is beta. The base connects to the anomeric carbon C1' of ribose either at N9 in purines (adenine and guanine) or at N1 in pyrimidines (cytosine and uracil).

Standard ribonucleosides include adenosine, guanosine, cytidine, and uridine. Modified ribonucleosides, such as inosine and pseudouridine, are common in cellular RNA and can influence structure, base pairing, and function. Ribonucleosides are distinct from deoxyribonucleosides, which contain a 2'-deoxyribose sugar lacking the 2'-hydroxyl.

When a ribonucleoside is phosphorylated, it becomes a ribonucleotide (for example AMP, GMP, CMP, UMP) and can be further converted to di- and triphosphates that supply substrates for RNA synthesis and cellular metabolism. Nucleosides can also be produced via salvage pathways in cells by attaching a ribose phosphate to a free base.

Ribonucleosides are the building blocks of RNA and serve as precursors for nucleotide synthesis. They also feature in various biologically active molecules, and nucleoside analogs are widely used as antiviral and anticancer therapies.