BRAINCAKEDNA Methylation
DNA methylation is the addition of a methyl group (CH3) to DNA. The methyl group is attached to the base cytosine, usually where cytosine is followed by guanine (a CpG site). Methylation is catalysed by enzymes called DNA methyltransferases. It does not change the base sequence.
Increased methylation of the DNA inhibits transcription. It does this in two ways:
• The methyl groups prevent transcription factors from binding to the DNA, especially in the promoter region.
• The methyl groups attract proteins that bind to them and make the chromatin more condensed, so the gene cannot be reached by transcription factors or RNA polymerase.
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More in Control of Gene Expression
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All 18 lessons in Control of Gene Expression · All AQA A-level Biology topics