This image depicts the chemical structure of cytosine. It shows a hexagonal ring with nitrogen atoms at positions 1 and 3, and a primary amine group attached to carbon 4. The two remaining positions ...

IN the nucleic acids, cytosine is connected to a sugar residue through N 1 of the pyrimidine ring. Here we describe the results of an X-ray diffraction analysis of crystals of N 1-methyl cytosine.