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BRCA1 and BRCA2 are human genes that code for tumour suppressor proteins - AQA - A-Level Biology - Question 10 - 2022 - Paper 1
Question 10
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. Genetic testing, u... 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 1
Step 1
Explain how mutations in BRCA1 and BRCA2 can cause cancer.
Answer
Mutations in BRCA1 and BRCA2 genes can lead to a change in DNA base sequence or triplet, resulting in the production of defective tumour suppressor proteins. This impairment can alter the protein's amino acid sequence, leading to dysfunctional protein function. Additionally, these mutations can result in altered primary or tertiary structures of the proteins, ultimately causing rapid or uncontrollable cell division, which is a hallmark of cancer development.
Step 2
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, DNA can be amplified using PCR (Polymerase Chain Reaction). Following amplification, the DNA is subjected to techniques such as restriction enzyme digestion or electrophoresis to separate DNA fragments. Labeled DNA probes are then added, which hybridize to specific mutated sequences. Visualization methods like fluorescence or radioactivity can help identify mutations based on the presence of specific bands on an electrophoresis gel.
Step 3
Suggest and explain how these drugs are an effective treatment of ER-positive breast cancers.
Answer
Drugs that mimic the structure of oestrogen can bind to the oestrogen receptors on ER-positive breast cancer cells. This binding can block the oestrogen hormone from exerting its effects, preventing the stimulation of cancer cell growth. Additionally, these drugs may lead to a decrease in the activity of transcription factors that promote the expression of genes responsible for cell proliferation, thereby inhibiting the progression of breast cancer.
Step 4
Explain why the results of blood tests may not be conclusive when testing for prostate cancer.
Answer
Blood tests for prostate cancer often measure the levels of Prostate-Specific Antigen (PSA). However, elevated PSA levels are not solely indicative of prostate cancer; they can also result from benign prostatic hyperplasia or prostatitis. This overlap can lead to false positives, rendering the blood tests inconclusive without further diagnostic evaluations.
Step 5
Suggest and explain how treatment with drugs might be able to reverse the epigenetic changes that cause cancers.
Answer
Treatment with certain drugs may involve the inhibition of enzymes that add methyl groups to DNA, which can silence genes involved in tumor suppression. By using demethylating agents, these drugs can potentially reverse the epigenetic modifications, thereby restoring the expression of silenced tumour suppressor genes. This reversal can lead to a reduction in uncontrolled cell proliferation, thereby impacting cancer progression.