Editing Cytosine

{{Short description|Chemical compound in nucleic acids}}
{{Distinguish|cytokine|cytidine|cysteine|cystine|cytisine}}
{{chembox
| Watchedfields  = changed
| verifiedrevid  = 443557332
| ImageFile1     = Cytosine structure 2022.svg
| ImageSize1     = 120px
| ImageClass1    = skin-invert-image
| ImageFile2     = Cytosine-3D-balls.png
| ImageSize2     = 180px
| ImageFile3     = Cytosine-3D-vdW.png
| ImageSize3     = 150px
| PIN            = 4-Aminopyrimidin-2(1''H'')-one
| OtherNames     = 4-Amino-1''H''-pyrimidine-2-one
| Section1       = {{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 577
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 15913
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C4H5N3O/c5-3-1-2-6-4(8)7-3/h1-2H,(H3,5,6,7,8)
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = OPTASPLRGRRNAP-UHFFFAOYSA-N
| CASNo = 71-30-7
| CASNo_Ref = {{cascite|correct|CAS}}
| PubChem = 597
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 8J337D1HZY
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 16040
| SMILES = O=C1Nccc(N)n1
| KEGG_Ref = {{keggcite|correct|kegg}}
| KEGG = C00380
| InChI = 1/C4H5N3O/c5-3-1-2-6-4(8)7-3/h1-2H,(H3,5,6,7,8)
| InChIKey = OPTASPLRGRRNAP-UHFFFAOYAY
| MeSHName = Cytosine
  }}
| Section2       = {{Chembox Properties
| Formula=C<sub>4</sub>H<sub>5</sub>N<sub>3</sub>O
| MolarMass=111.10 g/mol
| Appearance=
| Density= 1.55 g/cm<sup>3</sup> (calculated)
| MeltingPtC = 320 to 325
| MeltingPt_notes = (decomposes)
| BoilingPt=
| pKa=4.45 (secondary), 12.2 (primary)<ref>{{cite book | author = Dawson, R.M.C. | title = Data for Biochemical Research | location = Oxford | publisher = Clarendon Press | year = 1959|display-authors=etal}}</ref>
| Solubility= 
| MagSus = −55.8·10<sup>−6</sup> cm<sup>3</sup>/mol
  }}
| Section3       = {{Chembox Hazards
| MainHazards=
| FlashPt=
| AutoignitionPt =
  }}
}}

'''Cytosine''' ({{IPAc-en|ˈ|s|aɪ|t|ə|ˌ|s|iː|n|,_|-|ˌ|z|iː|n|,_|-|ˌ|s|ɪ|n}}<ref>{{Dictionary.com|Cytosine}}</ref><ref>{{MerriamWebsterDictionary|Cytosine}}</ref>) ([[nucleoside#List of nucleosides and corresponding nucleobases|symbol]] '''C''' or '''Cyt''') is one of the four [[nucleotide base]]s 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 [[Ketone|keto]] group at position 2). The [[nucleoside]] of cytosine is [[cytidine]].  In [[Watson–Crick base pair]]ing, it forms three [[hydrogen bond]]s with [[guanine]].

==History==
Cytosine was discovered and named by [[Albrecht Kossel]] and Albert Neumann in 1894 when it was hydrolyzed from calf [[thymus]] tissues.<ref>A. Kossel and Albert Neumann (1894) [http://gallica.bnf.fr/ark:/12148/bpt6k90735d/f437.image.langEN "Darstellung und Spaltungsprodukte der Nucleïnsäure (Adenylsäure)"] (Preparation and cleavage products of nucleic acids (adenic acid)), ''Berichte der Deutschen Chemischen Gesellschaft zu Berlin'', '''27''' :  2215–2222.  The name "cytosine" is coined on page 2219:  ''" … ein Produkt von basischen Eigenschaften, für welches wir den Namen "Cytosin" vorschlagen."'' ( … a product with basic properties, for which we suggest the name "cytosine".)</ref><ref>{{cite journal |author1=Kossel, A. |author2=Steudel, H. Z. | journal = Physiol. Chem. | year = 1903 | volume = 38 |issue=1–2 | pages = 49–59 | doi = 10.1515/bchm2.1903.38.1-2.49 | title = Weitere Untersuchungen über das Cytosin|url=https://zenodo.org/record/1448762 }}</ref> A structure was proposed in 1903, and was synthesized (and thus confirmed) in the laboratory in the same year.

In 1998, cytosine was used in an early demonstration of [[quantum information processing]]  when Oxford University researchers implemented the [[Deutsch–Jozsa algorithm]] on a two [[qubit]] [[Nuclear magnetic resonance quantum computer#Overview of Liquid State Nuclear Magnetic Resonance Quantum Information Processing|nuclear magnetic resonance quantum computer (NMRQC)]].<ref>{{cite journal | last = Jones | first = J.A. | author2 = M. Mosca | title = Implementation of a quantum algorithm on a nuclear magnetic resonance quantum computer | journal = J. Chem. Phys. | volume = 109 | issue = 5 | pages = 1648–1653 | date = 1998-08-01 | url = http://www.citebase.org/abstract?id=oai%3AarXiv.org%3Aquant-ph%2F9801027 | doi = 10.1063/1.476739 | access-date = 2007-10-18 | arxiv = quant-ph/9801027 | bibcode = 1998JChPh.109.1648J | s2cid = 19348964 | archive-url = https://web.archive.org/web/20080612133706/http://www.citebase.org/abstract?id=oai%3AarXiv.org%3Aquant-ph%2F9801027 | archive-date = 2008-06-12 | url-status = dead }}</ref>

In March 2015, NASA scientists reported the formation of cytosine, along with uracil and thymine, from [[pyrimidine]] under the space-like laboratory conditions, which is of interest because pyrimidine has been found in meteorites although its origin is unknown.<ref name="NASA-20150303">{{cite web |last=Marlaire |first=Ruth |title=NASA Ames Reproduces the Building Blocks of Life in Laboratory |url=http://www.nasa.gov/content/nasa-ames-reproduces-the-building-blocks-of-life-in-laboratory |date=3 March 2015 |work=[[NASA]] |access-date=5 March 2015 |archive-date=5 March 2015 |archive-url=https://web.archive.org/web/20150305083306/http://www.nasa.gov/content/nasa-ames-reproduces-the-building-blocks-of-life-in-laboratory/ |url-status=dead }}</ref>

==Chemical reactions==
<div class='skin-invert-image'>
{{multiple image
| align=left
| total_width = 360
| 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.
}}</div>
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>
{{clear}}

==Biological function==
When found third in a [[codon]] of [[RNA]], cytosine is synonymous with [[uracil]], as they are interchangeable as the third base.
When found as the second base in a codon, the third is always interchangeable. For example, UCU, UCC, UCA and UCG are all [[serine]], regardless of the third base.

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.<ref name="Chahwan">{{cite journal|author1=Chahwan R. |author2=Wontakal S.N. |author3=Roa S. | title=Crosstalk between genetic and epigenetic information through cytosine deamination| journal=Trends in Genetics| volume = 26| pages = 443–448| year = 2010 | doi = 10.1016/j.tig.2010.07.005| pmid = 20800313| issue = 10}}</ref> The implications of deamination on 5-hydroxymethylcytosine, on the other hand, remains less understood.

== Theoretical aspects ==
Until October 2021, Cytosine had not been found in meteorites, which suggested the first strands of RNA and DNA had to look elsewhere to obtain this building block. Cytosine likely formed within some meteorite parent bodies, however did not persist within these bodies due to an effective [[deamination]] reaction into [[uracil]].<ref>{{Cite news|url=https://blogs.scientificamerican.com/guest-blog/did-the-seeds-of-life-come-from-space/|title=Did the Seeds of Life Come from Space?|last=Tasker|first=Elizabeth|newspaper=Scientific American Blog Network|access-date=2016-11-24}}</ref>

In October 2021, Cytosine was announced as having been found in meteorites by researchers in a joint Japan/NASA project, that used novel methods of detection which avoided damaging nucleotides as they were extracted from meteorites.<ref>{{cite journal |author1=Yasuhiro Oba |author2=Yoshinori Takano |author3=Yoshihiro Furukawa |author4=Toshiki Koga |author5=Daniel P. Glavin |author6=Jason P. Dworkin |author7=Hiroshi Naraoka |title=Identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites |journal=Nature Communications |date=2022 |volume=13 |issue=1 |page=2008 |publisher=Nature.com |doi=10.1038/s41467-022-29612-x |pmid=35473908 |pmc=9042847 |bibcode=2022NatCo..13.2008O }}</ref>

==References==
{{Reflist|30em}}

==External links and citations==
{{Commons category|Cytosine}}
* [https://web.archive.org/web/20190416021636/http://gmd.mpimp-golm.mpg.de/Spectrums/04ef65b4-ae00-4bbf-b115-64d1aa7e0fcd.aspx Cytosine MS Spectrum]
*{{EINECSLink|200-749-5}}
* {{cite journal |author=Shapiro R |title=Prebiotic cytosine synthesis: a critical analysis and implications for the origin of life |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=96 |issue=8 |pages=4396–401 |year=1999 |pmid=10200273 |doi= 10.1073/pnas.96.8.4396|pmc=16343 |bibcode=1999PNAS...96.4396S |doi-access=free }}

{{Nucleobases, nucleosides, and nucleotides}}
{{Purinergics}}

{{Authority control}}

[[Category:Nucleobases]]
[[Category:Amines]]
[[Category:Pyrimidones]]