cytosine

 

(sī'tōsēn') , organic base of the pyrimidine family. It was isolated from the nucleic acid of calf thymus tissue in 1894. A suggested structure for cytosine, published in 1903, was confirmed in the same year when that base was synthesized in the laboratory. Combined with the sugar ribose in glycosidic linkage, cytosine forms a derivative called cytidine (a nucleoside), which in turn can be phosphorylated with from one to three phosphoric acid groups, yielding the three nucleotides CMP (cytidine monophosphate), CDP (cytidine diphosphate), and CTP (cytidine triphosphate). Analogous nucleosides and nucleotides are formed from cytosine and deoxyribose. The nucleoside derivatives of cytosine perform important functions in cellular metabolism. CTP acts as a coenzyme in both carbohydrate and lipid metabolism; it can readily donate one of its phosphate groups to adenosine diphosphate (ADP) to form adenosine triphosphate (ATP), an extremely important intermediate in the transfer of chemical energy in living systems. CTP is the source of the cytidine found in ribonucleic acid (RNA) and deoxycytidine triphosphate (dCTP) is the source of the deoxycytidine in deoxyribonucleic acid (DNA). Thus cytosine is intimately involved in the preservation and transfer of genetic information.

Cytosine
IUPAC name	4-amino-3H-pyrimidin-2-one
Identifiers
CAS number	71-30-7
PubChem	597
MeSH	Cytosine
SMILES	C1=C(NC(=O)N=C1)N
Properties
Molecular formula	C4H5N3O
Molar mass	111.102
Melting point	320 - 325°C (decomp)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Cytosine is one of the five main nucleobases found in the nucleic acids 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.

History

Cytosine was discovered by Albrecht Kossel in 1894 when it was hydrolysed from calf thymus tissues.^[1] 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.^[2]

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.

References

External links

• EINECS number 200-749-5
• Computational Chemistry Wiki
• Shapiro R (1999). "Prebiotic cytosine synthesis: a critical analysis and implications for the origin of life". Proc. Natl. Acad. Sci. U.S.A. 96 (8): 4396-401. PMID 10200273. 

Major families of biochemicals
Peptides | Amino acids | Nucleic acids | Carbohydrates | Lipids | Terpenes | Carotenoids | Tetrapyrroles | Enzyme cofactors | Steroids | Flavonoids | Alkaloids | Polyketides | Glycosides
Analogues of nucleic acids:	Types of Nucleic Acids	Analogues of nucleic acids:
Nucleobases:	Purine (Adenine, Guanine) | Pyrimidine (Uracil, Thymine, Cytosine)
Nucleosides:	Adenosine/Deoxyadenosine | Guanosine/Deoxyguanosine | Uridine | Thymidine | Cytidine/Deoxycytidine
Nucleotides:	monophosphates (AMP, UMP, GMP, CMP) | diphosphates (ADP, UDP, GDP, CDP) | triphosphates (ATP, UTP, GTP, CTP) | cyclic (cAMP, cGMP, cADPR)
Deoxynucleotides:	monophosphates (dAMP, TMP, dGMP, dCMP) | diphosphates (dADP, TDP, dGDP, dCDP) | triphosphates (dATP, TTP, dGTP, dCTP)
Ribonucleic acids:	RNA | mRNA | piRNA | tRNA | rRNA | ncRNA | gRNA | shRNA | siRNA | snRNA | miRNA | snoRNA
Deoxyribonucleic acids:	DNA | mtDNA | cDNA | plasmid | Cosmid | BAC | YAC | HAC
Analogues of nucleic acids:	GNA | PNA | TNA | Morpholino | LNA

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