BRAINCAKEDNA Methylation
DNA methylation is the addition of a methyl group (-CH3) to a cytosine base in DNA. It is one of the main epigenetic marks and usually switches genes off.
Where it happens
Methylation usually occurs where a cytosine is followed by a guanine in the base sequence. These sites are called CpG sites. Clusters of CpG sites, called CpG islands, are common in the promoter regions of genes. The methyl groups are added by enzymes called DNA methyltransferases. The base sequence is not changed: the cytosine is still read as cytosine.
How it silences a gene
When the promoter of a gene is heavily methylated:
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Key terms in this lesson
- tumour suppressor gene
- A gene whose protein product normally restrains cell division or promotes DNA repair, and whose loss of function can allow cancer to develop.
More in Gene Expression
- Control of Gene Expression
- Transcription Factors
- RNA Splicing
- Epigenetics
- DNA Demethylation
- Euchromatin and Heterochromatin
- Histone Acetylation
- Histone Methylation
All 39 lessons in Gene Expression · All Edexcel A-level Biology topics