ribosiidit

Ribosiidid, or ribosides, are a class of nucleosides in which a ribose sugar is linked to a nucleobase via a β-N-glycosidic bond. The sugar component is ribose, distinguishing ribosides from deoxyribonucleosides, which contain deoxyribose. The base portion can be adenine, cytosine, guanine, uracil, or related bases such as inosine. The four canonical ribonucleosides found in RNA are adenosine, cytidine, guanosine, and uridine; inosine also appears in certain RNA molecules, notably transfer RNA.

Natural occurrence and roles: Ribosides occur both as free molecules in cells and as components of RNA when phosphorylated to nucleotides. They arise from hydrolysis of nucleotides or from salvage pathways that recycle bases and sugars to regenerate nucleotides needed for RNA synthesis. Adenosine, in particular, serves as a signaling molecule in the nervous and cardiovascular systems, acting through purinergic receptors. In metabolism, ribosides are phosphorylated by specific kinases to form nucleotides used in RNA synthesis, energy transfer, and various biosynthetic processes.

Synthesis and applications: Ribosides can be produced chemically or enzymatically. In pharmacology, nucleoside analogs (which include riboside structures) are used as antiviral and anticancer agents after cellular phosphorylation; their activity depends on cellular kinases and metabolic activation. Beyond biology and medicine, ribosides are studied for their roles in nucleotide metabolism, signaling, and RNA biology, as well as for insights into the evolution of nucleotide synthesis pathways.