AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Epigenetic control of gene expression in eukaryotes.
Full specification wording
Regulation of transcription and translation (A-level only): Epigenetic control of gene expression in eukaryotes.
Epigenetic control determines which eukaryotic genes are transcribed, without altering the DNA base sequence.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 3 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Epigenetic control determines which eukaryotic genes are transcribed, without altering the DNA base sequence. DNA wraps around histones to form chromatin. How tightly it winds dictates if transcription factors and RNA polymerase can access the promoter. Increased methylation of cytosine bases in the promoter inhibits transcription by preventing protein binding and condensing chromatin. Conversely, adding acetyl groups to histones reduces their positive charge, weakening their attraction to DNA's phosphate groups. This loosens chromatin, stimulating transcription. Environmental factors alter these tags. These epigenetic changes can be maintained during DNA replication and passed to daughter cells, explaining how environmental influences can be heritable.
What earns the marks
- Increased methylation of DNA or the promoter region inhibits transcription.
- Decreased acetylation of associated histones inhibits transcription, while increased acetylation stimulates it.
- Less acetylation makes histones bind DNA more tightly, condensing DNA so transcription factors or RNA polymerase cannot bind.
- The base sequence of the DNA remains unchanged during epigenetic modification.
- Environmental factors can alter epigenetic tags, and these changes can be passed on to daughter cells during replication.
Common mistakes and how to put them right
Swapping the pairs and writing 'methylation of histones' or 'acetylation of DNA', which is incorrect.
Put it right: Learn the specific pairings of DNA methylation and histone acetylation.
Stating 'the gene is switched off' without linking it to the inhibition of transcription or gene expression.
Put it right: Use precise terms like 'transcription is inhibited'.
Calling an epigenetic change a mutation.
Put it right: Explicitly state that the DNA base sequence is unchanged.
Claiming that epigenetic changes cannot be inherited.
Put it right: Epigenetic tags can be maintained during DNA replication and passed to daughter cells.
Exam tips
- Learn the pairing: methylation of DNA, acetylation of histones. Mixing them up loses marks.
- Always convert 'switched on or off' into 'transcription is stimulated or inhibited'.
Try the lesson
The start of the Regulation of transcription and translation (A-level only): Epigenetic control of gene expression in eukaryotes. lesson, made from checked teaching notes for this specification point.
Have a go first
Which of the following best describes epigenetic control of gene expression in eukaryotes?
Listen
Epigenetic control determines which eukaryotic genes are transcribed, without altering the DNA base sequence. DNA wraps around histones to form chromatin. How tightly it winds dictates if transcription factors and RNA polymerase can access the promoter. Increased methylation of cytosine bases in the promoter inhibits transcription by preventing protein binding and condensing chromatin. Conversely, adding acetyl groups to histones reduces their positive charge, weakening their attraction to DNA's phosphate groups. This loosens chromatin, stimulating transcription. Environmental factors alter these tags. These epigenetic changes can be maintained during DNA replication and passed to daughter cells, explaining how environmental influences can be heritable. A strong answer earns marks for these points. Increased methylation of DNA or the promoter region inhibits transcription. Decreased acetylation of associated histones inhibits transcription, while increased acetylation stimulates it. Less acetylation makes histones bind DNA more tightly, condensing DNA so transcription factors or RNA polymerase cannot bind. The base sequence of the DNA remains unchanged during epigenetic modification. A common slip: Swapping the pairs and writing 'methylation of histones' or 'acetylation of DNA', which is incorrect. Instead, learn the specific pairings of DNA methylation and histone acetylation. Exam tip: Learn the pairing: methylation of DNA, acetylation of histones. Mixing them up loses marks.
Key words
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epigenetics
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DNA methylation
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histone acetylation
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environment and gene expression
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See every definition
- epigenetics
- Control that determines which eukaryotic genes are transcribed, without altering the DNA base sequence.
- DNA methylation
- Increased methylation of cytosine bases in the promoter inhibits transcription by preventing protein binding and condensing chromatin.
- histone acetylation
- Adding acetyl groups to histones reduces their positive charge, weakening their attraction to DNA's phosphate groups and loosening chromatin to stimulate transcription.
- environment and gene expression
- Environmental factors alter epigenetic tags, and these changes can be maintained during DNA replication and passed to daughter cells.
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