Cytosinbase

Cytosinbase is the cytosine base, one of the four nucleobases in the nucleic acids DNA and RNA. It is a pyrimidine with a single-ring structure and an exocyclic amino group. In DNA, cytosine pairs with guanine through three hydrogen bonds, forming C–G base pairs; in RNA, cytosine also pairs with guanine within RNA duplexes and structured regions. Cytosine exists in deoxyribonucleotide form (deoxycytidine monophosphate, dCMP) and ribonucleotide form (cytidine monophosphate, CMP); these nucleotides serve as building blocks for DNA and RNA synthesis by polymerases.

Cytosine can be chemically modified. In many organisms, the 5-position can be methylated to form 5-methylcytosine, an important epigenetic mark in DNA. Further oxidation yields derivatives such as 5-hydroxymethylcytosine, involved in dynamic demethylation and epigenetic regulation. Cytosine is susceptible to deamination, producing uracil, which triggers base-excision repair pathways to maintain genome integrity. In vertebrates, deamination of methylated cytosine more commonly yields thymine, contributing to characteristic mutation patterns.

In biology and medicine, cytosine and its derivatives are central to sequencing, methylation analysis, and diagnostic assays. Techniques such as bisulfite sequencing distinguish cytosine from 5-methylcytosine, enabling genome-wide maps of cytosine methylation. Cytosine is universally present in cellular genomes and transcripts, reflecting its essential role in genetic information storage and expression.