AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
The role of the following in the development of tumours: tumour suppressor…
Full specification wording
Gene expression and cancer (A-level only): The role of the following in the development of tumours: tumour suppressor genes and oncogenes abnormal methylation of tumour suppressor genes and oncogenes increased oestrogen concentrations in the development of some breast cancers.
Two classes of gene normally keep cell division in balance.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 2 of 2
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Two classes of gene normally keep cell division in balance. Proto-oncogenes code for proteins that stimulate division. A mutation can turn a proto-oncogene into an oncogene, whose protein is permanently active or overproduced, so the cell divides uncontrollably. Tumour suppressor genes (TSGs) code for proteins that slow the cell cycle, repair DNA or trigger apoptosis. A mutation can inactivate a TSG, so damaged cells survive and divide. These outcomes also arise epigenetically: hypermethylation of a TSG's promoter prevents its transcription, while reduced methylation of an oncogene increases it. Increased oestrogen concentrations can also stimulate mitosis in some breast cancers.
What earns the marks
- A mutation converting a proto-oncogene into an oncogene whose protein is permanently active or overproduced.
- The outcome being rapid or uncontrollable cell division.
- A mutated or hypermethylated tumour suppressor gene producing no protein or a non-functional protein, so the cell cycle is not stopped.
- Increased methylation of DNA inhibiting transcription, and decreased methylation stimulating transcription.
- Increased oestrogen concentration stimulating transcription of genes that drive mitosis in breast tissue.
Common mistakes and how to put them right
Writing that the oncogene produces no protein or a non-functional protein, when an oncogene's product is overactive or overproduced.
Reversing the methylation directions and stating that tumour suppressor genes are hypomethylated in cancer.
Answering 'growth' instead of cell division or mitosis.
Saying meiosis rather than mitosis when describing the division of tumour cells.
Exam tips
- Both routes end in the same outcome - rapid or uncontrollable cell division - so make that your final point.
- Decide first whether the question is about a mutation or about methylation, as the mechanisms differ.
- When discussing oestrogen, mention that it can stimulate transcription of genes that lead to cell division.
Try the lesson
The start of the Gene expression and cancer (A-level only): The role of the following in the development of tumours: tumour suppressor genes and oncogenes abnormal methylation of tumour suppressor genes and oncogenes increased oestrogen concentrations in the development of some breast cancers. lesson, made from checked teaching notes for this specification point.
Have a go first
Which type of gene normally codes for proteins that slow the cell cycle and so help to prevent the formation of tumours?
Listen
Two classes of gene normally keep cell division in balance. Proto-oncogenes code for proteins that stimulate division. A mutation can turn a proto-oncogene into an oncogene, whose protein is permanently active or overproduced, so the cell divides uncontrollably. Tumour suppressor genes (TSGs) code for proteins that slow the cell cycle, repair DNA or trigger apoptosis. A mutation can inactivate a TSG, so damaged cells survive and divide. These outcomes also arise epigenetically: hypermethylation of a TSG's promoter prevents its transcription, while reduced methylation of an oncogene increases it. Increased oestrogen concentrations can also stimulate mitosis in some breast cancers. A strong answer earns marks for these points. a mutation converting a proto-oncogene into an oncogene whose protein is permanently active or overproduced. the outcome being rapid or uncontrollable cell division. a mutated or hypermethylated tumour suppressor gene producing no protein or a non-functional protein, so the cell cycle is not stopped. increased methylation of DNA inhibiting transcription, and decreased methylation stimulating transcription. Exam tip: Both routes end in the same outcome - rapid or uncontrollable cell division - so make that your final point.
Key words
Say what each word means before you turn the card.
oncogenes
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tumour suppressor genes
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abnormal methylation
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oestrogen and breast cancer
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See every definition
- oncogenes
- A mutation can turn a proto-oncogene into one of these, whose protein is permanently active or overproduced, so the cell divides uncontrollably.
- tumour suppressor genes
- These code for proteins that slow the cell cycle, repair DNA or trigger apoptosis, and a mutation can inactivate them so damaged cells survive and divide.
- abnormal methylation
- Hypermethylation of a tumour suppressor gene's promoter prevents its transcription, while reduced methylation of an oncogene increases it.
- oestrogen and breast cancer
- Increased concentrations can stimulate mitosis in some breast cancers by stimulating transcription of genes that drive mitosis in breast tissue.
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