|Jmol-3D images||Image 1|
|Molar mass||111.10 g/mol|
|Density||1.55 g/cm3 (calculated)|
320-325 °C, 593-598 K, 608-617 °F (decomp.)
|Acidity (pKa)||4.45 (secondary), 12.2 (primary)|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Cytosine // (C) is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an amine group at position 4 and a keto group at position 2). The nucleoside of cytosine is cytidine. In Watson-Crick base pairing, it forms three hydrogen bonds with guanine.
Cytosine was discovered by Albrecht Kossel in 1894 when it was hydrolyzed from calf thymus tissues. A structure was proposed in 1903, and was synthesized (and thus confirmed) in the laboratory in the same year.
Cytosine recently found use in quantum computation. The first time any quantum mechanical properties were harnessed to process information took place on August 1 in 1998 when researchers at Oxford implemented David Deutsch's algorithm on a two qubit nuclear magnetic resonance quantum computer (NMRQC) based on cytosine.
Chemical reactions 
Cytosine can be found as part of DNA, as part of RNA, or as a part of a nucleotide. As cytidine triphosphate (CTP), it can act as a co-factor to enzymes, and can transfer a phosphate to convert adenosine diphosphate (ADP) to adenosine triphosphate (ATP).
In DNA and RNA, cytosine is paired with guanine. However, it is inherently unstable, and can change into uracil (spontaneous deamination). This can lead to a point mutation if not repaired by the DNA repair enzymes such as uracil glycosylase, which cleaves a uracil in DNA.
Cytosine can also be methylated into 5-methylcytosine by an enzyme called DNA methyltransferase or be methylated and hydroxylated to make 5-hydroxymethylcytosine. Active enzymatic deamination of cytosine or 5-methylcytosine by the APOBEC family of cytosine deaminases could have both beneficial and detrimental implications on various cellular processes as well as on organismal evolution. The implications of deamination on 5-hydroxymethylcytosine, on the other hand, remains less understood.
- Dawson, R.M.C., et al. (1959). Data for Biochemical Research. Oxford: Clarendon Press.
- Kossel, A.; Steudel, H. Z. (1903). "Weitere Untersuchungen über das Cytosin". Physiol. Chem. 38: 49. doi:10.1515/bchm2.1903.38.1-2.49.
- Jones, J.A.; M. Mosca (1998-08-01). "Implementation of a quantum algorithm on a nuclear magnetic resonance quantum computer". J.Chem.Phys 109 (109): 1648–1653. doi:10.1063/1.476739. Retrieved 2007-10-18.
- Chahwan R., Wontakal S.N., and Roa S. (2010). "Crosstalk between genetic and epigenetic information through cytosine deamination". Trends in Genetics 26 (10): 443–448. doi:10.1016/j.tig.2010.07.005. PMID 20800313.
- EINECS number 200-749-5
- Shapiro R (1999). "Prebiotic cytosine synthesis: a critical analysis and implications for the origin of life". Proc. Natl. Acad. Sci. U.S.A. 96 (8): 4396–401. doi:10.1073/pnas.96.8.4396. PMC 16343. PMID 10200273.