Guanine

Guanine is one of the four main nucleobases in DNA and RNA. It is a purine derivative with the chemical formula C5H5N5O and is commonly described as 2-amino-6-oxopurine. In physiological conditions, guanine exists predominantly in the form that features an amino group at the 2-position and a carbonyl at the 6-position.

In nucleic acids, guanine pairs with cytosine via three hydrogen bonds, helping to stabilize the DNA double helix and the RNA structure. This G–C pairing is a key contributor to the genetic code’s fidelity and the overall stability of nucleic acids.

Guanine is also a component of guanine nucleotides— GMP, GDP, and GTP— and their deoxy counterparts dGMP, dGDP, and dGTP. These nucleotides are used in RNA synthesis and DNA replication, and GTP in particular serves as an energy source and an activated substrate for protein synthesis and various signaling processes, including G-protein–mediated pathways.

Biosynthesis and salvage of guanine occur through cellular purine metabolism. Guanine can be produced in de novo purine biosynthesis, and it can be salvaged from guanine to form GMP via the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT).

Guanine can undergo chemical and enzymatic modifications, and oxidative damage can yield lesions such as 8-oxoguanine, which can mispair during replication if not repaired. Overall, guanine is a fundamental building block of genetic material and a pivotal player in cellular metabolism.