Cytosine

Cytosine is one of the pyrimidine bases present in the composition of nucleic acids.

Structure of cytosine

Cytosine is a nitrogen base belonging to the pyrimidine family, which has the chemical formula C₄H₅N₃O. It is therefore a heterocyclic molecule, as the rings are not only composed of carbon.

Function of cytosine

Cytosine is involved in the formation of cytidine (in which cytosine is bound to a ribose) which is present in the composition of nucleic acids (DNA and RNA), CMP, CDP and CTP.

Cytosine is bound to guanine in nucleic acids by three hydrogen bonds.

Cytosine is the only base that can be methylated in DNA, an epigenetic change that alters the expression of genes.