Explain how a mutation in a cell's DNA can lead to the development of cancer.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Cancer is one of the most common diseases in the UK. It occurs when normal body cells begin to divide in an uncontrolled way, forming a tumour. Scientists know that certain factors can increase the likelihood of cancer developing.
Model answer (5 marks)
A mutation is a change in the DNA base sequence of a cell.
Mutations can arise spontaneously or be caused by mutagens such as radiation or carcinogenic chemicals in cigarette smoke.
The mutation may affect genes that control cell division and growth, for example proto‑oncogenes or tumour‑suppressor genes.
The altered gene causes the cell to divide uncontrollably or to ignore normal growth‑inhibitory signals.
This uncontrolled proliferation produces a mass of abnormal cells, i.e. a tumour.
Mutations can arise spontaneously or be caused by mutagens such as radiation or carcinogenic chemicals in cigarette smoke.
The mutation may affect genes that control cell division and growth, for example proto‑oncogenes or tumour‑suppressor genes.
The altered gene causes the cell to divide uncontrollably or to ignore normal growth‑inhibitory signals.
This uncontrolled proliferation produces a mass of abnormal cells, i.e. a tumour.
Examiner tips
- Use the exact terms: mutation, DNA, proto‑oncogene, tumour‑suppressor gene, uncontrolled division, tumour.
- Show the causal chain: mutation → gene affected → loss of control → tumour.
- Keep each point concise to match the 5‑mark structure.
Common mistakes
- Confusing mutation with mutation rate or mutation type; students often write ‘mutation rate’ instead of ‘mutation’. Failing to mention mutagens or giving only one cause. Using vague phrases like ‘abnormal cells’ without linking to uncontrolled division.
Mark scheme (5 marks)
- A mutation is a change in the DNA (base sequence / genetic code) of a cell
- Mutations can occur spontaneously or be caused by mutagens (e.g. radiation, carcinogens such as chemicals in cigarette smoke)
- The mutation affects genes that control cell division / growth
- The mutated cell divides uncontrollably / does not respond to normal growth signals
- This uncontrolled division produces a mass of abnormal cells called a tumour
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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