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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 the BRCA1 and BRCA2 genes disrupt their normal functions as tumour suppressor proteins.
- Change in DNA Base Sequence: A mutation often results in a change in the DNA base sequence or triplet, leading to incorrect replication of genetic material.
- Amino Acid Sequence Alteration: This can result in a change in the sequence of amino acids in the protein, thereby affecting protein folding and function.
- Impact on Cell Division: Consequently, this can lead to rapid and uncontrollable cell division as the regulatory mechanisms that prevent tumor growth are compromised.
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, the following steps can be undertaken:
- Sample Collection: Obtain a saliva sample from the individual for DNA extraction.
- PCR Amplification: Utilize Polymerase Chain Reaction (PCR) to amplify specific DNA sequences of interest.
- DNA Sequencing: Perform DNA sequencing to identify changes in the sequence, allowing all known harmful mutations to be detected by comparison with reference sequences.
- Genetic Analysis: Analyze the sequence data to pinpoint any mutations linked to cancer susceptibility.
Step 3
Suggest and explain how these drugs are an effective treatment of ER-positive breast cancers.
Answer
The drugs used for treating ER-positive breast cancer often resemble oestrogen in structure. Their effectiveness can be attributed to:
- Binding to Estrogen Receptor: These drugs bind to estrogen receptors (ER) in breast cells, inhibiting the hormone's action.
- Prevention of Hormone Activity: By blocking the receptor, they prevent estrogen from promoting cell division and tumor growth, essentially starving the cancer of the stimulus it requires to proliferate.
Step 4
Explain why the results of blood tests may not be conclusive when testing for prostate cancer.
Answer
Blood tests for prostate cancer, typically measuring prostate-specific antigen (PSA) levels, have limitations because:
- False Positives: Elevated PSA levels can indicate conditions other than cancer, such as an enlarged prostate or urinary infection, leading to false positive results.
- Variability of PSA Levels: PSA levels can fluctuate significantly, and not all prostate cancers produce high PSA levels, resulting in inconclusive test outcomes.
Step 5
Suggest and explain how treatment with drugs might be able to reverse the epigenetic changes that cause cancers.
Answer
Drugs may reverse epigenetic changes through several mechanisms:
- DNA Methylation Modifiers: These treatment options can include agents that inhibit the enzymes responsible for adding methyl groups to DNA, which typically silence gene expression.
- Histone Modifications: Additionally, certain therapies may target histone modifications, facilitating the unpackaging of DNA and restoring expression of genes that suppress tumor formation, thus reversing the cancerous state.