nucleotidi

Nucleotides are the basic monomers of nucleic acids, the polymers that store and transmit genetic information. A nucleotide consists of three components: a nitrogenous base (purine or pyrimidine), a five‑carbon sugar (deoxyribose in DNA, ribose in RNA), and one to three phosphate groups. When the phosphate is absent, the molecule is a nucleoside. Nucleotides carrying one, two, or three phosphate groups are called NMP, NDP, and NTP, respectively.

The bases include purines (adenine and guanine) and pyrimidines (cytosine, thymine in DNA, and uracil in RNA). In DNA the sugar is deoxyribose, whereas in RNA it is ribose. Nucleotides join through phosphodiester bonds between the 3′ hydroxyl of one sugar and the 5′ phosphate of the next, forming the sugar–phosphate backbone of nucleic acids.

Beyond their role as genetic material, nucleotides function in energy transfer and signaling. ATP and GTP are primary energy currencies; cyclic AMP and cyclic GMP act as intracellular signaling molecules. Nucleotides also serve as cofactors and activated intermediates in metabolism (for example NAD+, NADP+, FAD, CoA). Cells synthesize nucleotides de novo or reclaim them via salvage pathways to maintain balanced nucleotide pools. Enzymes called kinases interconvert NMPs, NDPs, and NTPs, enabling DNA replication and transcription, RNA synthesis, and various metabolic reactions to proceed efficiently.