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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 lead to a change in the DNA base sequence, which can alter the structure of the proteins they produce. As a result, this change can affect the primary or tertiary structure of the proteins, leading to their dysfunction. Consequently, this results in rapid and uncontrolled cell division, which is a hallmark 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
The screening process may involve several steps. First, a sample of saliva is collected to extract DNA. Then, Polymerase Chain Reaction (PCR) is used to amplify the specific regions of DNA that are associated with harmful mutations. This is followed by the separation of DNA fragments using gel electrophoresis. The amplified DNA is then compared with a known sequence of the BRCA1 and BRCA2 genes to identify any mutations present.
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 work by binding to the oestrogen receptors on the cancer cells. By binding to these receptors, the drugs prevent oestrogen from attaching, thereby inhibiting the cancer cells' growth. This is effective because it disrupts the normal signaling pathways that promote cell division and survival in the presence of oestrogen.
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
The blood test for prostate cancer measures the concentration of prostate-specific antigen (PSA), which can be elevated due to various conditions, not just cancer. This could include benign enlargement of the prostate, infections, or other non-cancerous conditions, leading to false positives that make the tests inconclusive.
Step 5
Treatment with drugs might be able to reverse the epigenetic changes that cause cancers (lines 16–17). Suggest and explain how.
Answer
These drugs could target and modify epigenetic markers, such as methylation patterns on oncogenes and tumor suppressor genes. By reducing the methylation of these genes, the drugs can restore normal transcription and expression, potentially reversing the cancerous changes. Additionally, alterations in histone acetylation may also be targeted, further influencing gene expression favorable to normal cellular function.