nukleozidet

Nukleozidet, or nucleosides, are compounds that form a key part of nucleic acids. They consist of a nitrogenous base, which can be a purine or a pyrimidine, attached to a sugar molecule (ribose in RNA or deoxyribose in DNA) by a beta-N-glycosidic bond. Nucleosides differ from nucleotides in that they lack one or more phosphate groups.

The four common bases lead to several nucleosides: adenosine and guanosine (from adenine and guanine) and cytidine and uridine (from cytosine and uracil) in RNA, with their deoxyribonucleoside counterparts—deoxyadenosine, deoxyguanosine, deoxycytidine, and thymidine—in DNA. Thymidine is the deoxyribonucleoside corresponding to thymine, whereas uridine is the ribonucleoside corresponding to uracil.

Nukleozidet are formed in cells through salvage pathways, where bases are recycled, or via de novo synthesis. They can be phosphorylated by kinases to form nucleotides (monophosphates, diphosphates, and triphosphates), which are essential substrates for nucleic acid synthesis by RNA and DNA polymerases.

In addition to their structural role in nucleic acids, nukleozidet participate in cellular metabolism and signaling. Nucleoside analogs, which modify or mimic natural nucleosides, have clinical importance as antiviral and anticancer agents (for example, AZT and acyclovir), illustrating the biomedical relevance of these compounds.