Deoxynucleosides

Deoxynucleosides are the glycosylamine components of DNA, consisting of a 2'-deoxyribose sugar covalently linked to one of the four nitrogenous bases: adenine, guanine, cytosine, or thymine. They lack the phosphate group that characterizes nucleotides. The sugar is the 2'-deoxyribose, and the glycosidic bond is typically beta, connecting the C1' of the sugar to a nitrogen on the base.

In terms of bonding, purine bases (adenine and guanine) attach to the sugar via the N9 atom, while pyrimidine bases (cytosine and thymine) attach via the N1 atom. The result is a flat, ring-stacked structure that forms the building block for DNA when linked to phosphates.

Biological role and metabolism: deoxynucleosides themselves do not carry phosphate, but they are central intermediates in nucleotide metabolism. They can arise from dephosphorylation of nucleotides or through salvage pathways in cells. Kinases then phosphorylate them to deoxynucleotides, supplying substrates for DNA synthesis and repair.

Medical relevance: deoxynucleoside analogs are important in medicine. Some modified deoxynucleosides mimic natural ones but disrupt DNA synthesis when phosphorylated, serving as antiviral or anticancer agents. Examples include zidovudine (AZT) and lamivudine (3TC), which are used as antiviral drugs, as well as other analogs studied for therapeutic purposes.