nucleotider

Nucleotides are the basic building blocks of nucleic acids, consisting of three components: a sugar molecule, one or more phosphate groups, and a nitrogenous base. The sugar is ribose in RNA and deoxyribose in DNA. The bases are purines (adenine and guanine) and pyrimidines (cytosine and thymine in DNA; cytosine and uracil in RNA). Nucleotides exist in active forms with one, two, or three phosphate groups, such as monophosphates, diphosphates, and triphosphates.

Nucleotides polymerize to form nucleic acids through phosphodiester bonds, linking the 5' phosphate of one nucleotide to the 3' hydroxyl of the next. In DNA, the typical nucleotides are deoxyribonucleoside triphosphates (dATP, dCTP, dGTP, dTTP), whereas RNA uses ribonucleoside triphosphates (ATP, CTP, GTP, UTP). Base pairing between nucleotides encodes genetic information: in DNA, adenine pairs with thymine and guanine pairs with cytosine; in RNA, adenine pairs with uracil.

Beyond genetic information storage and transcription, nucleotides play crucial roles in metabolism and signaling. ATP and GTP are primary energy carriers; cyclic nucleotides such as cyclic AMP (cAMP) and cyclic GMP (cGMP) act as second messengers in signal transduction. Nucleotides also form essential cofactors, including nicotinamide adenine dinucleotide (NAD+), flavin adenine dinucleotide (FAD), and coenzyme A, which participate in redox reactions and metabolic pathways. Nucleotide pools are maintained by de novo synthesis and salvage pathways to support DNA replication, transcription, translation, and energy metabolism.