| PubChem=597 | SMILES=C1=C(NC(=O)N=C1)N | MeSHName=Cytosine }} |Section2 = |Section3= }} Cytosine's one of the four main bases found in DNA and RNA. It's a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at position 2). The nucleoside of cytosine's cytidine. In Watson-Crick base pairing, it forms three hydrogen bonds with guanine. History Cytosine was discovered by Albrecht Kossel in 1894 when it was hydroly… (More on Cytosine)