Puriinien

Puriinien are a class of nitrogen-containing heterocyclic compounds that form the nucleobases found in DNA and RNA. The principal purine nucleobases are adenine and guanine. Purines are distinguished by a fused double-ring structure, and in nucleic acids they pair with pyrimidines (adenine with thymine in DNA or uracil in RNA, and guanine with cytosine) to encode genetic information.

Beyond their role in nucleic acids, purine nucleotides function as essential energy carriers and signaling molecules. ATP and GTP supply chemical energy for numerous cellular processes, while cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) act as intracellular second messengers. Purine nucleotides are also components of a variety of cofactors and macromolecules, including nicotinamide adenine dinucleotide (NAD+), flavin adenine dinucleotide (FAD), and coenzyme A, which all rely on purine sequences for their activity.

Purine biosynthesis occurs through two main pathways: de novo synthesis and salvage. In de novo synthesis, a ribose-5-phosphate backbone is converted through a series of steps to inosine monophosphate (IMP), which is then converted to AMP or GMP. The salvage pathways recycle purine bases from degraded nucleotides via enzymes such as hypoxanthine-guanine phosphoribosyltransferase (HGPRT) and adenine phosphoribosyltransferase (APRT), conserving cellular resources.

Metabolism of purines culminates in the production of uric acid in humans, which is excreted in urine. In many mammals, urate oxidase converts uric acid to allantoin, a more soluble compound. Disorders of purine metabolism can lead to elevated uric acid and gout, or, in cases of enzyme deficiencies, to various metabolic and developmental abnormalities. Purines are ubiquitous across life, reflecting their fundamental roles in genetics, metabolism, and cellular signaling.