Cytosine

=**Cytosine**=

**Cytosine ** (often abbreviated to **C **, chemical formula C4H5N3O) is a nitrogenous nucleobase, one of the four commonly found in DNA. When forming part of a deoxynucleotide, the compound is called **deoxycytidine monophosphate ** (dCMP), and it is attached to a growing DNA chain by addition of a **deoxycytidine triphosphate **(dCTP) precursor. It may also be found in RNA where its monomeric constituent is called simply **cytidine monophosphate **(CMP) from a **cytidine triphosphate ** (CTP) precursor.

 Cytosine is a pyrimidine derivative, and it base-pairs with guanine using three hydrogen bonds. Cytosine is often found methylated in eukaryotic genomes to form 5'-methylcytosine.