AskDefine | Define cytosine

Dictionary Definition

cytosine n : a base found in DNA and RNA and derived from pyrimidine; pairs with guanine [syn: C]

User Contributed Dictionary



After German Cytosin, from cyto- + -ose + -ine.




  1. A base, C4H5N3O, which pairs with guanine in DNA and RNA.

Extensive Definition

distinguish cysteine
Cytosine is one of the five main bases found in DNA and 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 hydrolysed 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 1st in 1998 when researchers at Oxford implemented David Deutsch's algorithm on a two qubit NMRQC (Nuclear Magnetic Resonance Quantum Computer) based on the cytosine molecule.

Chemical reactions

Cytosine can be found as part of DNA, 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.


External links

cytosine in Catalan: Citosina
cytosine in Czech: Cytosin
cytosine in Danish: Cytosin
cytosine in German: Cytosin
cytosine in Spanish: Citosina
cytosine in Esperanto: Citozino
cytosine in French: Cytosine
cytosine in Galician: Citosina
cytosine in Indonesian: Sitosin
cytosine in Italian: Citosina
cytosine in Hebrew: ציטוזין
cytosine in Lithuanian: Citozinas
cytosine in Dutch: Cytosine
cytosine in Japanese: シトシン
cytosine in Norwegian: Cytosin
cytosine in Occitan (post 1500): Citosina
cytosine in Polish: Cytozyna
cytosine in Portuguese: Citosina
cytosine in Russian: Цитозин
cytosine in Simple English: Cytosine
cytosine in Slovenian: Citozin
cytosine in Serbian: Цитозин
cytosine in Serbo-Croatian: Citozin
cytosine in Finnish: Sytosiini
cytosine in Swedish: Cytosin
cytosine in Vietnamese: Cytosine
cytosine in Turkish: Sitozin
cytosine in Ukrainian: Цитозин
cytosine in Chinese: 胞嘧啶
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