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Methylation is a form of alkylation, i.e. the transfer of an alkyl group to another molecule. Methylation is specifically the addition or substition of a methyl group to a molecule. Methyl groups are alkyls made from methane and are carbon atoms attached to 3 hydrogen atoms -CH3[1]. It can be involved in the expression of genes, as well as protein function regulation and the metabolism of RNA. An example of this is the tri-methylation of lysine 36 on the H3 protein (of a histone), which is involved in the response of plants to necrotrophic fungal attack[2]

Methylation of a gene, addition of a methyl group (-CH3)[1], is catalyzed by the family of enzymes DNA-methyltransferases (DNMTs) and occurs at the 5-carbon on a cytosine ring; the methyl group projects into the major groove of the DNA double helix, causing the DNA-histone complex to become more tightly condensed, which prevents/negatively affects the binding of transcriptional factors to promoter regions or induces deacetylation of the histone proteins which inhibits transcription of the DNA sequence to mRNA.


  1. March's Advanced Organic Chemistry. Michael B. Smith, Jerry March - John Wiley and Sons (2007)
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