Ribonukleotidreduktasen

Ribonucleotides are the monomers and key metabolites of RNA, composed of a ribose sugar, a nitrogenous base (adenine, guanine, cytosine, or uracil), and one to three phosphate groups. The phosphate groups can form ribonucleoside monophosphates (NMPs), diphosphates (NDPs), or triphosphates (NTPs). The presence of a hydroxyl group on the 2' carbon of ribose distinguishes ribonucleotides from deoxyribonucleotides, which are used to build DNA. NTPs—especially ATP, GTP, CTP, and UTP—serve as substrates for RNA synthesis, while ATP and GTP also function as cellular energy currencies. Cyclic forms such as cyclic AMP (cAMP) and cyclic GMP (cGMP) act as signaling molecules.

In cells, ribonucleotides are synthesized by both de novo and salvage pathways. De novo synthesis starts from ribose-5-phosphate, proceeds through phosphoribosyl pyrophosphate (PRPP), and yields the various NMPs, NDPs, and NTPs needed for RNA production. Salvage pathways recycle free bases and nucleosides to restore nucleotide pools, conserving energy and resources. Ribonucleotide reductase converts ribonucleotides to their deoxyribonucleotide counterparts, providing precursors for DNA replication and repair and linking RNA and DNA metabolism.

Ribonucleotides are also catabolized to nucleosides and bases, which can be reused or excreted. Dysregulation of nucleotide metabolism can affect cell growth and has clinical relevance, as many chemotherapy agents target nucleotide synthesis or turnover. Beyond genetics, ribonucleotides play a central role in various cellular processes and in laboratory techniques such as in vitro transcription and enzymatic assays.