Sitosina: Perbedaan antara revisi
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Pada keadaan tertentu, sitosina dapat mengalami [[deaminasi]] menjadi [[urasil]]. Mutasi ini biasanya dapat dikenali oleh enzim-enzim yang terlibat dalam [[reparasi DNA]]. Sebagaimana pada urasil, [[metilasi]] juga dapat terjadi pada sitosin dengan bantuan enzim DNA-metil-transferase.
==Sejarah ==
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▲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 Spaltunsprodukte 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 | author = Kossel, A.; Steudel, H. Z. | journal = Physiol. Chem. | year = 1903 | volume = 38 | pages = 49 | doi = 10.1515/bchm2.1903.38.1-2.49 | title = Weitere Untersuchungen über das Cytosin}}</ref> 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|David Deutsch's]] [[Deutsch-Jozsa algorithm|algorithm]] on a two [[qubit]] [[nuclear magnetic resonance]] quantum computer (NMRQC) based on cytosine.<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 = 109 | pages = 1648–1653 | publisher = | date = 1998-08-01 | url = http://www.citebase.org/abstract?id=oai%3AarXiv.org%3Aquant-ph%2F9801027 | doi = 10.1063/1.476739 | id = | accessdate = 2007-10-18 }}</ref>
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== Reaksi kimia ==
[[File:Cytosine chemical structure.svg|thumb|left|100px|
Sitosina dapat ditemukan sebagai bagian [[DNA]], dan bagian [[RNA]], atau sebagai bagian dari suatu [[nukleotida]]. Sebagai [[cytidine triphosphate]] (CTP), dapat berfungsi sebagai ko-faktor enzim-enzim, dan dapat mentransfer suatu gugus fosfat untuk mengubah [[ADP|adenosine diphosphate]] (ADP) menjadi [[ATP|adenosine triphosphate]] (ATP).
Dalam DNA dan RNA, sitosina berpasangan dengan [[guanina]]. Namun, ikatan ini secara inheren tidak stabil, dan dapat diubah menjadi [[urasil]] ([[:en:deamination|deaminasi spontan]]). Ini dapat menghasilkan suatu [[point mutation]] jika tidak diperbaiki oleh enzim-enzim [[DNA repair]] seperti urasil glikosilase, yang memutus suatu urasil dalam DNA.
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▲[[File:Cytosine chemical structure.svg|thumb|left|100px|Cytosine with numbered components. [[Methylation]] occurs on carbon nr 5.]]
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]].
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| author= Chahwan R., Wontakal S.N., and 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.
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