Editing Cytosine (section)

==Chemical reactions==
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| image1=Cytonum2.svg
| caption1=Cytosine
| image2=Guannum2.svg
| caption2=[[Guanine]]
| footer=Cytosine and guanine with the direction of hydrogen bonding indicated (arrow points positive to negative charge).<br>[[Methylation]] of cytosine occurs on carbon number 5.
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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]] ([[Deamination#Cytosine|spontaneous deamination]]). This can lead to a [[point mutation]] if not repaired by the [[DNA repair]] [[enzyme]]s such as uracil glycosylase, which cleaves a uracil in DNA.

Cytosine can also be [[Methylation|methylated]] into [[5-Methylcytosine|5-methylcytosine]] by an enzyme called [[DNA methyltransferase]] or be methylated and [[Hydroxylation|hydroxylated]] to make [[5-Hydroxymethylcytosine|5-hydroxymethylcytosine]]. The difference in rates of deamination of cytosine and 5-methylcytosine (to uracil and [[thymine]]) forms the basis of [[bisulfite sequencing]].<ref>{{Cite journal|last=Hayatsu|first=Hikoya|date=2008|title=Discovery of bisulfite-mediated cytosine conversion to uracil, the key reaction for DNA methylation analysis — A personal account|journal=Proceedings of the Japan Academy. Series B, Physical and Biological Sciences|volume=84|issue=8|pages=321–330|doi=10.2183/pjab.84.321|issn=0386-2208|pmc=3722019|pmid=18941305|bibcode=2008PJAB...84..321H}}</ref>
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