Cytosine
Cytosine is one of the four Nitrogenous bases found in DNA and RNA along with Adenine, Guanine, Thymine and Uracil.
It is described as a Pyrimidine base, meaning it is a single six-member ring.
Cytosine always pairs up with Guanine, forming three hydrogen bonds between itself and Guanine.
[LM]
{GE}
{RH}