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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 BRCA1 and BRCA2 can lead to changes in the DNA sequence, specifically altering the triplet code responsible for protein synthesis. This can result in the production of nonfunctional proteins or a complete lack of these proteins, disrupting normal cellular processes. Consequently, the inability to regulate cell division effectively can lead to unchecked cellular proliferation, promoting tumor development.
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 in the BRCA genes using saliva DNA, the process would typically employ Polymerase Chain Reaction (PCR) to amplify specific target regions of the DNA. The DNA would be extracted, cut into fragments by restriction enzymes, and then subjected to gel electrophoresis to separate these fragments. By labeling the amplified strands and using mutations that are identified through comparisons with a known DNA sequence, researchers can pinpoint harmful mutations that have been documented.
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 act as competitive inhibitors that bind to oestrogen receptors (ER) on the cancer cells. By mimicking oestrogen, these drugs prevent the actual hormone from binding and activating these receptors, which could otherwise lead to increased cell division and cancer growth. Ultimately, this action inhibits the transcription of genes that promote tumor cell proliferation, making it an effective strategy in managing ER-positive breast cancers.
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 for prostate cancer often measure the concentration of prostate-specific antigen (PSA). However, factors such as benign prostatic hyperplasia or urinary infections can cause fluctuations in PSA levels, leading to potential false positives. Therefore, PSA levels alone may not provide a definitive conclusion regarding 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 designed for reversing epigenetic changes can target specific modifications on DNA and histones. For example, they may inhibit enzymes responsible for adding methyl groups to oncogenes, thereby reactivating tumor suppressor genes that were silenced. By modifying these epigenetic marks, the treatment can potentially restore normal transcriptional activity and halt cancer progression.