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)
4-aminopyrimidin-2(1H)-one
References
click on the picture of Cytosine above to interact
with the 3D model of the
Cytosine structure
(this will open a new browser window)
C4 H5 N3 O
Update by Karl Harrison
(Molecule of the Month for
July 2019
)
All the images on this web site are are made available with a Creative Commons Attribution license and so can be used as long as the attribution © Karl Harrison 3DChem.com is written with the image. High resolution images and illustrations are available on request.