Nukleotidy

Nukleotidy (nucleotides) are the fundamental building blocks of nucleic acids, comprising a nitrogenous base, a five‑carbon sugar, and one to three phosphate groups. In DNA and RNA, the sugar is deoxyribose or ribose, respectively. Nucleotides can exist as monophosphates, diphosphates, or triphosphates.

The bases are purines (adenine, guanine) and pyrimidines (cytosine, thymine in DNA, uracil in RNA). The sugar-base moiety determines whether the nucleotide is DNA or RNA, and the phosphate group forms the backbone via phosphodiester bonds linking the 3' and 5' carbons.

Functions: Nucleotides store and transmit genetic information (DNA), participate in transcription and RNA processing. They also serve as energy carriers (ATP, GTP) and as signaling molecules (cAMP, cGMP) and as cofactors for enzymes (NAD+, FAD, CoA).

Synthesis and turnover: Nucleotides are synthesized de novo or via salvage pathways from free bases. Purine nucleotides are built stepwise on ribose-5-phosphate; pyrimidines are assembled first, then attached to ribose-5-phosphate. Salvage pathways recycle bases using phosphoribosyltransferases. Regulatory control occurs at key steps, such as PRPP amidotransferase in purine synthesis and feedback inhibition by ATP or CTP.

In biochemistry and molecular biology, nucleotides also function as substrates for nucleic acid polymerization during replication and transcription, and as components of ribozymes and ribonucleoprotein complexes.