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Read the following passage - AQA - A-Level Biology - Question 10 - 2022 - Paper 2
Question 10
Read the following passage. BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins. Mutations in BRCA1 and BRCA2 can cause cancer. Specific inheri... show full transcript
Worked Solution & Example Answer:Read the following passage - AQA - A-Level Biology - Question 10 - 2022 - Paper 2
Step 1
BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins. Mutations in BRCA1 and BRCA2 can cause cancer (lines 1–2). Explain how.
Answer
Mutations in the BRCA1 and BRCA2 genes can lead to a change in the DNA base sequence, which may result in an altered protein product or ineffective proteins. This can impact the genes' ability to suppress tumour formation effectively, causing uncontrolled cell division and increasing the risk of cancer.
Step 2
Genetic testing, using DNA from saliva, can screen for all known harmful mutations in both genes (lines 5–6). Describe how this DNA could be screened for all known harmful mutations in both genes.
Answer
To screen for harmful mutations, DNA from saliva can be collected and amplified using PCR (Polymerase Chain Reaction). The DNA is then cut with restriction enzymes, and the resulting fragments are separated through gel electrophoresis. Labeled DNA probes specific to known harmful mutations can bind to the fragments to highlight any existing mutations.
Step 3
Effective treatment of ER-positive breast cancers often involves the use of drugs which have a similar structure to oestrogen (lines 9–10). Suggest and explain how these drugs are an effective treatment of ER-positive breast cancers.
Answer
These drugs can bind to oestrogen receptors in breast cancer cells, preventing the actual hormone oestrogen from binding. This inhibition reduces the stimulation of cancer cell growth and division, inhibiting the proliferation of ER-positive breast cancer cells.
Step 4
Blood tests can be used to test for cancers (line 11). However, the results of blood tests may not be conclusive when testing for prostate cancer. Explain why.
Answer
Blood tests measuring prostate-specific antigen (PSA) levels may yield false positives, as elevated PSA levels can occur due to conditions other than prostate cancer, such as urinary infections or benign prostatic hyperplasia. Therefore, high PSA levels alone cannot confirm the presence of prostate cancer.
Step 5
Treatment with drugs might be able to reverse the epigenetic changes that cause cancers (lines 16–17). Suggest and explain how.
Answer
Drugs that target the epigenetic modification processes can lead to decreased methylation of oncogenes and increased expression of tumour suppressor genes. For example, certain drugs can inhibit enzymes that add methyl groups to DNA, thus restoring the normal expression patterns of genes involved in cell cycle regulation and apoptosis, which may help in reversing tumorigenesis.