Monday 22 November 2004
Definition: Nucleosides are molecules formed by attaching a nucleobase to a ribose ring. Examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine.
Nucleosides are glycosylamines made by attaching a nucleobase to a ribose ring. Examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine.
Nucleosides can be phosphorylated by specific kinases in the cell, producing nucleotides, which are the molecular building blocks of DNA and RNA.
Nucleosides are produced as the second step in nucleic acid digestion, when 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 are involved in signaling in a number of physiologic systems, and synthetic analogs of natural nucleosides are used to treat neoplastic and viral diseases.
Plasma membrane transport of nucleosides is mediated by equilibrative and concentrative nucleoside transporters, which may have specificity for purines or pyrimidines.