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Cytosine (Molecule of the Month for July 2019)

Nucleobase, DNA

Cytosine 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 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.

Formal Chemical Name (IUPAC)



Picture of Cytosine 3D model

click on the picture of  Cytosine above to interact
with the 3D model of the
Cytosine structure
(this will open a new browser window)

Picture of Cytosine

C4 H5 N3 O

Update by Karl Harrison
(Molecule of the Month for July 2019 )

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