BRAINCAKEDNA Demethylation
DNA demethylation is the removal of methyl groups from cytosine bases in DNA. It reverses DNA methylation, so a gene that had been silenced can be switched back on.
How it happens
• Passive demethylation: if the maintenance methyltransferase is inactive when DNA replicates, the new strands are not methylated. With each round of cell division, the proportion of methylated DNA halves.
• Active demethylation: enzymes chemically modify the methyl groups on cytosines and the modified bases are then replaced with ordinary cytosine. This can happen without cell division.
Effect on gene expression
When the methyl groups are removed from a promoter, transcription factors and RNA polymerase can bind again and the chromatin can become less tightly packed, so the gene can be transcribed.
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Key terms in this lesson
- oncogene
- A gene that, when mutated or overexpressed, can drive a cell towards becoming cancerous.
- 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
- Transcription Factors
- RNA Splicing
- Epigenetics
- DNA Methylation
- Euchromatin and Heterochromatin
- Histone Acetylation
- Histone Methylation
- non-Coding RNA
All 39 lessons in Gene Expression · All Edexcel A-level Biology topics