Cytosine (C)

Cytosine is a fundamental pyrimidine nucleobase that serves as one of the four primary building blocks of DNA and RNA. In the DNA double helix, it pairs specifically with guanine through three hydrogen bonds, a critical interaction for maintaining the structural integrity and accurate replication of the genome (Genome.gov, 2024). Beyond its role in genetic coding, cytosine is the central substrate for DNA methylation, an essential epigenetic mechanism where the addition of a methyl group to the 5-position of the cytosine ring regulates gene expression and cellular identity (NIH, 2023). While cytosine itself is a metabolite and not a traditional therapeutic target like a protein receptor or enzyme, it is the structural basis for a wide array of nucleoside analog drugs. These pharmacological agents, such as cytarabine and gemcitabine, are designed to mimic cytosine and are used to treat various malignancies and viral infections by disrupting nucleic acid synthesis or modulating DNA methylation patterns (DrugBank, 2024; PubChem, 2024).

Other names

4-aminopyrimidin-2(1H)-one4-amino-2-hydroxypyrimidineCyt71-30-7

Nucleoside analogs act as antimetabolites by being phosphorylated into active triphosphates that compete with natural cytosine for incorporation into DNA or RNA, leading to chain termination or DNA damage; others act as suicide inhibitors of DNA methyltransferases (DNMTs) to reverse gene silencing (StatPearls, 2023; DrugBank, 2024).