A level Biology B · Edexcel 9BI0 · Topic 7B
Gene expression and epigenetics
Key points
- Every cell has the same genes, but different cells express different genes, which is how cells become specialised.
- Transcription factors bind to promoter regions to switch transcription on or off.
- Epigenetics: heritable changes in gene expression without changing the base sequence.
- DNA methylation (adding methyl groups to cytosine) usually silences genes.
- Histone modification: acetylation loosens chromatin so genes can be transcribed; removing acetyl groups packs DNA tightly and stops transcription.
- Epigenetic marks can be influenced by the environment (diet, stress, toxins) and some may pass to offspring.
- RNA interference: small RNA molecules bind mRNA and stop it being translated. In the bacterial lac operon, lactose removes a repressor so the genes for lactose use are transcribed.
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Almost every cell in your body contains the same genome, yet a liver cell and a neurone make very different proteins. The difference lies in which genes are switched on, and this is controlled at several levels, from transcription to the…
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