Guanin

Guanin (also guanine in English) is one of the four primary nucleobases found in DNA and RNA. It is a purine base with the chemical formula C5H5N5O and is systematically named 2-amino-6-oxopurine. In nucleic acids, guanine forms three hydrogen bonds with cytosine, contributing to the stability of the double helix.

Chemically, guanine features an amino group at position 2 and a keto group at position 6 on the purine ring. The predominant tautomer under physiological conditions is the lactam form; the base is planar and aromatic. The free base can exist in several tautomeric forms, but the lactam form is most relevant for base-pairing.

Biological role and metabolism: Guanine is incorporated into nucleic acids as dGMP in DNA and GMP in RNA, with corresponding triphosphates dGTP and GTP serving as substrates for polymerases. It is produced in cells by de novo purine biosynthesis and via salvage pathways from guanine or guanosine. Deamination of guanine yields xanthine; oxidative damage can produce 8-oxoguanine, an oxidized lesion linked to mutagenesis if unrepaired.

Occurrence and significance: Guanine is ubiquitous in all living organisms and is essential for genetic information storage and transfer. It is also used in biochemical research and diagnostic applications, and its derivatives participate in various cellular processes beyond nucleic acids.