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BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins - AQA - A-Level Biology - Question 10 - 2022 - Paper 2
Question 10
BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins. Mutations in BRCA1 and BRCA2 can cause cancer. Specific inherited mutations in these genes ... show full transcript
Worked Solution & Example Answer:BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins - 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 changes in the DNA base sequence, ultimately affecting the amino acids that are produced during protein synthesis. This can result in a nonfunctional or malfunctioning protein that fails to perform its normal role of regulating cell division. Consequently, cells may begin to divide uncontrollably, leading to tumorigenesis.
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 BRCA1 and BRCA2 genes from saliva, the DNA would first be extracted from the saliva sample. PCR (Polymerase Chain Reaction) would be employed to amplify the specific regions of the genes of interest. Next, the amplified DNA could be analyzed using techniques such as gel electrophoresis to separate the DNA fragments. Finally, DNA sequencing might be used to directly compare the amplified sequences with known sequences of both genes to identify any 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
Drugs that mimic oestrogen can bind to the oestrogen receptors on the target cancer cells. This binding can effectively block the real oestrogen from attaching to its receptor, preventing the activation of pathways that would otherwise stimulate cell growth and proliferation. Consequently, this can slow down or halt the growth of the 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 for prostate cancer often measure the levels of prostate-specific antigen (PSA). However, elevated PSA levels may not exclusively indicate cancer and could be influenced by other factors such as benign prostatic hyperplasia (enlarged prostate) or prostatitis (inflammation). Therefore, while PSA levels can suggest an increased risk of prostate cancer, they are not definitive on their own.
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 could potentially reverse epigenetic changes by altering the methylation patterns of DNA or histones. For instance, they may decrease the methylation of oncogenes, leading to an increase in the expression of tumor suppressor genes. Alternatively, drugs might inhibit histone deacetylases, leading to increased acetylation of histones, which promotes the transcription of genes that suppress tumors, helping revert the cancerous state.