AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
The relevance of epigenetics on the development and treatment of disease,…
Full specification wording
Regulation of transcription and translation (A-level only): The relevance of epigenetics on the development and treatment of disease, especially cancer.
Cancer arises when the epigenome is disrupted as well as when genes mutate.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 5 of 7
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Cancer arises when the epigenome is disrupted as well as when genes mutate. In many tumours the promoter region of a tumour suppressor gene becomes hypermethylated, so it is not transcribed; the protein that would normally slow the cell cycle or trigger apoptosis is not made, and damaged cells keep dividing. Oncogenes can be affected the other way: reduced methylation or increased acetylation of histones associated with the oncogene means it is transcribed more, so cell division is stimulated. Because no base has been altered, these changes are in principle reversible, which is what makes them attractive drug targets. Drugs that inhibit DNA methyltransferase reduce methylation of tumour suppressor genes so they are expressed again, while histone deacetylase inhibitors increase acetylation, loosening the chromatin and allowing transcription.
What earns the marks
- Increased methylation of a tumour suppressor gene promoter, so the gene is not transcribed and the protein that slows the cell cycle or triggers apoptosis is not made.
- Decreased methylation or increased acetylation of histones associated with an oncogene, so it is transcribed more and cell division is stimulated.
- Linking the methylation or acetylation change to inhibiting or stimulating transcription or expression of the gene.
- Explaining that the change is reversible because the base sequence of the DNA is not altered.
- Naming a drug class and its effect, such as a DNA methyltransferase inhibitor reducing methylation so a tumour suppressor gene is expressed again, or a histone deacetylase inhibitor increasing acetylation.
Common mistakes and how to put them right
Offering epigenetic modification as the explanation when the question is about a mutation causing a tumour - examiners ignore epigenetics in that context and want a change in base sequence.
Put it right: State that a mutation changes the base sequence, whereas epigenetic changes do not.
Reversing the treatment logic and methylating the tumour suppressor gene rather than reducing its methylation.
Put it right: A tumour suppressor gene needs to be re-expressed, so its methylation should be reduced.
Writing 'acetylation of DNA' or 'methylation of histones' in a treatment answer.
Put it right: Acetylation occurs on histones, methylation can occur on DNA or histones.
Saying an epigenetic drug 'cures cancer' without naming the enzyme inhibited or the effect on transcription.
Put it right: Name the enzyme and state the effect on transcription.
Confusing an epigenetic silencing of a tumour suppressor gene with the gene being deleted.
Put it right: The gene is still present but not transcribed.
Exam tips
- Keep two columns in your head: a tumour suppressor gene needs re-expressing, an oncogene needs silencing, and work out the methylation direction from that.
- Read whether the question asks for the cause of a tumour or a possible treatment - the same facts are marked differently.
- Reversibility is the usual 'why is this a promising treatment' mark; say the base sequence is unchanged.
Try the lesson
The start of the Regulation of transcription and translation (A-level only): The relevance of epigenetics on the development and treatment of disease, especially cancer. lesson, made from checked teaching notes for this specification point.
Have a go first
In many cancer cells, the promoter of a tumour-suppressor gene becomes more heavily methylated than in normal cells. What is the most likely consequence of this increased methylation?
Listen
Cancer arises when the epigenome is disrupted as well as when genes mutate. In many tumours the promoter region of a tumour suppressor gene becomes hypermethylated, so it is not transcribed; the protein that would normally slow the cell cycle or trigger apoptosis is not made, and damaged cells keep dividing. Oncogenes can be affected the other way: reduced methylation or increased acetylation of histones associated with the oncogene means it is transcribed more, so cell division is stimulated. Because no base has been altered, these changes are in principle reversible, which is what makes them attractive drug targets. Drugs that inhibit DNA methyltransferase reduce methylation of tumour suppressor genes so they are expressed again, while histone deacetylase inhibitors increase acetylation, loosening the chromatin and allowing transcription. A strong answer earns marks for these points. Increased methylation of a tumour suppressor gene promoter, so the gene is not transcribed and the protein that slows the cell cycle or triggers apoptosis is not made. Decreased methylation or increased acetylation of histones associated with an oncogene, so it is transcribed more and cell division is stimulated. Linking the methylation or acetylation change to inhibiting or stimulating transcription or expression of the gene. Explaining that the change is reversible because the base sequence of the DNA is not altered. A common slip: Offering epigenetic modification as the explanation when the question is about a mutation causing a tumour - examiners ignore epigenetics in that context and want a change in base sequence. Instead, state that a mutation changes the base sequence, whereas epigenetic changes do not. Exam tip: Keep two columns in your head: a tumour suppressor gene needs re-expressing, an oncogene needs silencing, and work out the methylation direction from that.
Key words
Say what each word means before you turn the card.
hypermethylation of tumour suppressor genes
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oncogene expression
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reversibility
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methyltransferase and HDAC inhibitors
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See every definition
- hypermethylation of tumour suppressor genes
- The promoter region of a tumour suppressor gene becomes hypermethylated, so it is not transcribed and the protein that would slow the cell cycle or trigger apoptosis is not made.
- oncogene expression
- Reduced methylation or increased acetylation of histones associated with the oncogene means it is transcribed more, so cell division is stimulated.
- reversibility
- Because no base has been altered, these changes are in principle reversible, which is what makes them attractive drug targets.
- methyltransferase and HDAC inhibitors
- Drugs that inhibit DNA methyltransferase reduce methylation of tumour suppressor genes so they are expressed again, while histone deacetylase inhibitors increase acetylation, loosening the chromatin and allowing transcription.
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