C4H5N3O

C4H5N3O, commonly known as cytosine, is one of the four main nucleobases found in DNA and RNA. It is a heterocyclic aromatic amine belonging to the pyrimidine class. The molecule features a six-membered pyrimidine ring with an exocyclic amino group at the 4-position and a carbonyl group at the 2-position, giving it the formula C4H5N3O.

In genetics, cytosine pairs with guanine through three hydrogen bonds, contributing to the stability and specific pairing of genetic information in DNA. Cytosine is present in RNA as well, where it also pairs with guanine. A common biochemical event involving cytosine is its deamination to uracil, which can lead to mutations if not repaired by cellular proofreading mechanisms.

Cytosine is synthesized in cells via the pyrimidine biosynthetic pathway and is incorporated into nucleic acids during replication and transcription. It can also be prepared synthetically for use in research, diagnostics, and biotechnological applications. In addition to its role in natural nucleic acids, cytosine derivatives are investigated for therapeutic and diagnostic potential.

Physical and chemical properties of cytosine include its classification as a polar, water-soluble solid at ambient conditions. It is relatively stable under physiological conditions but can undergo hydrolysis or oxidative processes under certain environments. Understanding cytosine and its interactions with complementary bases is foundational to studies of genetics, molecular biology, and biochemistry.