5-Methylcytosine

4-amino -5-methyl -1H -pyrimidine -2-one

Crystalline solid

Fixed

> 270 ° C

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5-methylcytosine is a heterocyclic organic compound with a Pyrimidingrundgerüst. It is a derivative of cytosine nucleobase with an additional methyl group in position 5, this substitution pattern correspond to the analogy between uracil and thymine. 5-methylcytosine is the nucleosides 5 - methylcytidine ( 5mC, m5C ) in the RNA and 5- methyldeoxycytidine (5- MEDC ) in the DNA.

Properties

Physical Properties

5-methylcytosine is a crystalline solid melting at about 270 ° C.

Chemical Properties

Due to its chemical instability, it can deaminate to thymine.

Biological Significance

5 - methylcytosine adjacent to 5 - hydroxymethylcytosine, the only modified DNA base that is found in mammals. Therefore, 5 -methylcytosine is often called the fifth and 5- hydroxymethylcytosine often referred to as the sixth DNA base. 5-methylcytosine is used in vivo postreplikativ formed ( according to the DNA synthesis ) from cytosine by addition of a methyl group ( DNA methylation ). This reaction is catalyzed by DNA methyltransferases ( DNMTs ).

5 -methylcytosine plays an important role in epigenetics and is on the Activation and Deactivation of genes and probably also involved in the organization of DNA in chromosomes.

Under physiological conditions, a small fraction of deaminated deoxycytidine contained in the DNA at deoxyuridine, for which special repair systems exist in cells. In the deamination of 5 - methyldeoxycytidine but the deoxythymidine also normally contained in the DNA, which can not be detected as faulty, which can mate in the next round of replication with deoxyadenosine, which then yields a transition from deoxycytidine by deoxythymidine and on the created opposite DNA strand will yield of deoxyguanosine by deoxyadenosine.