Cytosine
4-amino -1H- pyrimidin- 2-one
Colorless plates
Fixed
> 300 ° C
Moderately in boiling water and ethanol, insoluble in diethyl ether
Attention
-221.3 KJ / mol
Template: Infobox chemical / molecular formula search available
Cytosine (C, Cyt ) is one of four major nucleobases in DNA and RNA together with adenine, guanine, and thymine ( uracil in RNA). Is a heterocyclic organic compound with a Pyrimidingrundgerüst and two substituents ( an amino group at position 4 and a keto group at position 2). The nucleoside of cytosine is the deoxycytidine in DNA and cytidine in the RNA. In the Watson -Crick base pairing, it forms three hydrogen bonds with guanine.
- 3.1 nucleosides
- 3.2 nucleotides
- 3.3 part of DNA and RNA
History, Production and representation
The cytosine was first obtained in 1894 from the thymus gland of calves.
1903, the chemical structure by the later Nobel laureate Albrecht Kossel was elucidated and the first successful synthesis performed.
Properties
Physical Properties
Cytosine forms colorless plates having a melting point of over 300 ° C. It dissolves in boiling water and ethanol as standard, it is insoluble in diethyl ether.
Cytosine tautomer, wherein the 1H- form is predominant.
Chemical Properties
Due to its chemical instability of cytosine can deaminate to uracil.
Biological Significance
Cytosine may be part of the DNA, RNA, or various nucleosides and nucleotides.
Nucleosides
About the N1 atom of the ring cytosine can be bound N- glycosidically linked to the C1 atom of the ribose; this is called a nucleoside, the cytidine. When bound to deoxyribose nucleoside produced deoxycytidine. If cytosine, however, bound via the C5 atom of the ring at the C1 atom of the ribose C- glycoside, the result is the synthetic Pseudocytidin. The cytarabine contains - in contrast to most nucleosides - instead of ribose, arabinose.
Nucleotides
About the phosphorylation of cytidine on the C5 atom of the ribose leads to the important nucleotides cytidine monophosphate (CMP ), cytidine diphosphate (CDP ) and cytidine triphosphate (CTP ), and analogously for the deoxycytidine to Desoxycytidinmonophosphat ( dCMP ), Desoxycytidindiphosphat ( dCDP ) and deoxycytidine triphosphate ( dCTP ).
As cytidine triphosphate (CTP ), it serves as a cofactor for various enzymes and can release its phosphate group to ADP to build ATP.
Part of the DNA and RNA
In the DNA double helix cytosine on the oxo group, the N3 atom and the amino group forms three hydrogen bonds with the corresponding guanine base of the complementary strand.
In the methylated form 5 -methylcytosine is converted by cytosine - specific methyltransferases.