Nucleoside

Nucleosides are glycosylamines made by attaching a nucleobase (often referred to simply as bases) to a ribose or deoxyribose ring. Examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine. In short, a nucleoside is a base linked to sugar.

Nucleosides can be phosphorylated by specific kinases in the cell, producing nucleotides, which are the molecular building blocks of DNA ( a base linked to sugar and one or more phospate) and RNA (A category title for viruses, Ribonucleic acid).

Nucleosides are produced as the second step in nucleic acid digestion, whereby nucleotidases break down nucleotides (such as the thymine nucleotide) into nucleosides (such as thymidine) and phosphate. The nucleosides, in turn, are subsequently broken down:
 * - in the lumen of the digestive system by nucleosidases into nitrogenous bases and ribose (or deoxyribose).
 * - inside the cell by nucleoside phosphorylases into nitrogenous bases, and ribose-1-phosphate (or deoxyribose-1-phosphate).

Nucleosides differ from nucleotides by having a hydroxyl group attached to carbon number 5 (the one that isn't in the ring) of the ribose, rather than one or more phosphate groups.

