Sytosiinit

Sytosiinit is a term used in some languages to denote cytosine, one of the four primary nucleobases in DNA and RNA. It is a pyrimidine base that participates in base pairing and genetic information storage.

Chemical properties: Cytosine has a pyrimidine ring with a carbonyl group at position 2 and an amino group at position 4, giving the chemical name 4-amino-2(1H)-pyrimidinone. Its formula is C4H5N3O. In nucleic acids, cytosine pairs with guanine through three hydrogen bonds, contributing to the stability of the double helix.

Biological role and modifications: Cytosine can be methylated at the 5-position to form 5-methylcytosine, an important epigenetic mark in vertebrates. Oxidized derivatives such as 5-hydroxymethylcytosine also occur in genomes and have roles in gene regulation. Cytosine can undergo deamination to uracil, which is a common source of C to T mutations if not repaired. In RNA, cytosine also base-pairs with guanine.

Occurrence and relevance: Cytosine is universal across life, embedded in DNA and RNA. It is a common subject in biochemistry and molecular biology. Cytosine analogs and derivatives are used in research and medicine, including DNA methylation–inhibiting drugs such as azacytidine and decitabine, and in sequencing technologies that rely on cytosine chemistry.