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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 alter the DNA sequence that encodes for tumour suppressor proteins. This change can lead to a deficiency in these proteins' ability to regulate cell division, which may promote rapid and uncontrolled cell proliferation. Consequently, the normal mechanisms that prevent the growth of tumors become compromised, significantly increasing cancer risk.
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 DNA sample collected from saliva can be amplified using Polymerase Chain Reaction (PCR). The DNA is cut into fragments, which are then separated by gel electrophoresis. Specific primers that target the BRCA1 and BRCA2 genes can be used to identify any mutations present. Finally, sequencing the DNA allows for a comparison to known mutation sequences, thus enabling the identification of harmful 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, which mimic oestrogen, bind to oestrogen receptors on cancer cells. By occupying these receptors, the drugs prevent actual oestrogen from binding, thereby inhibiting its growth-promoting effects. This action interrupts the signal that stimulates cancer cell proliferation, effectively slowing down or stopping the growth of ER-positive breast tumors.
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 PSA levels are not exclusively indicative of prostate cancer; they can also be elevated due to benign conditions such as infection or inflammation of the prostate. Consequently, elevated PSA levels might result from non-cancerous factors, making it difficult to conclusively diagnose prostate cancer solely based on PSA test results.
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 targeting epigenetic modifications can alter the methylation status of oncogenes and tumour suppressor genes. For example, demethylating agents can decrease the methylation of tumor suppressor genes, thereby restoring their expression and function, which is often silenced in cancers. Additionally, histone deacetylase inhibitors can lead to increased acetylation, promoting the transcription of silenced genes, ultimately reversing the effects of epigenetic changes responsible for cancer.