OxfordAQA International A Level Biology
OxfordAQA International A Level Biology 3.2.11 Mutation and Cancer Exam Questions
Free OxfordAQA International A Level Biology revision for 3.2.11 Mutation and Cancer: what you need to know, common mistakes and exam-style questions with answers. Covers base substitutions and deletions, mutagens, benign and malignant tumours, oncogenes and tumour suppressor genes.
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About OxfordAQA International A Level Biology 3.2.11 Mutation and Cancer
Mutation and cancer closes Unit 2. You need to explain that gene mutations are changes in the base sequence that arise spontaneously during DNA replication, that mutagenic agents increase their rate, and how base substitution and deletion affect the amino acid sequence. Because the genetic code is degenerate, some substitutions have no effect. The cancer section covers benign and malignant tumours, proto-oncogenes, oncogenes and tumour suppressor genes. You should also analyse cancer risk data and relate the cell cycle to cancer drugs. It links to protein synthesis, mitosis and the epigenetic control of genes in Unit 4.
What you need to know
- Gene mutations A gene mutation is a change in the base sequence of DNA. It occurs spontaneously during DNA replication, and mutagenic agents such as ionising radiation and some chemicals increase the mutation rate.
- Substitution and deletion A substitution replaces one base with another and changes at most one triplet, so it may change one amino acid or none because the code is degenerate. A deletion causes a frame shift, changing every triplet after it and usually the whole protein.
- Tumours Benign tumours grow slowly, are enclosed in a capsule and do not spread. Malignant tumours grow quickly, can invade other tissues and spread by metastasis.
- Oncogenes Proto-oncogenes stimulate cell division. A mutated proto-oncogene, an oncogene, can be permanently switched on, causing excessive division.
- Tumour suppressor genes Tumour suppressor genes slow cell division. If a mutation inactivates them, cells divide too fast and a tumour may form.
- Cancer drugs Many cancer drugs act on the cell cycle, for example by blocking DNA replication or the formation of spindle fibres, so they mainly affect rapidly dividing cells.
Common mistakes in 3.2.11 Mutation and Cancer
- Saying all mutations change the protein. Substitutions can produce a triplet coding for the same amino acid.
- Saying a deletion changes one amino acid. It causes a frame shift, so all following triplets change.
- Saying tumour suppressor genes become oncogenes. Oncogenes come from mutated proto-oncogenes; tumour suppressor genes are inactivated.
- Saying benign tumours are harmless. They can still cause damage by pressing on organs, but they do not spread.
Try three 3.2.11 Mutation and Cancer exam-style questions
1. Explain why a base deletion usually has a greater effect than a base substitution. (3 marks)
Show the mark scheme answer
Deletion causes a frame shift; all triplets after the mutation are changed; so many amino acids change and the protein is likely to be non-functional, whereas a substitution changes at most one amino acid.
2. Explain how a mutation in a tumour suppressor gene can lead to cancer. (2 marks)
Show the mark scheme answer
Mutation inactivates the gene so its protein is not made or does not work; cell division is no longer slowed so it becomes uncontrolled, forming a tumour.
3. Give two differences between benign and malignant tumours. (2 marks)
Show the mark scheme answer
Malignant grow faster; malignant can spread / metastasise; benign are enclosed in a capsule; malignant invade surrounding tissue. (Any 2)
3.2.11 Mutation and Cancer FAQs
What does OxfordAQA International A Level Biology 3.2.11 Mutation and Cancer cover?
It covers base substitutions and deletions, mutagens, benign and malignant tumours, oncogenes and tumour suppressor genes.
Which unit is 3.2.11 Mutation and Cancer examined in?
It is part of Unit 2, Biological systems and disease, which is examined at International AS. The Unit 5 synoptic paper at A2 can also draw on this content.
What are the required practicals in Unit 2?
Unit 2 includes three required practicals: preparing a stained root tip squash to observe mitosis and calculate a mitotic index; investigating the effect of a variable on heart or pulse rate; and using a simple potometer to measure the rate of water uptake.
