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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 can lead to cancer primarily through several mechanisms:
- Change in DNA Base Sequence: Mutations can alter the DNA sequence or triplet coding. This may lead to faulty proteins that cannot effectively function in tumor suppression.
- Amino Acid Sequence Changes: Alterations in the DNA sequence can lead to changes in the resulting amino acid sequence in the protein, potentially affecting protein structure and function.
- Structural Changes: If mutations change the protein’s primary or tertiary structure, this may impede its ability to bind to DNA or interact with other critical molecules, leading to loss of function in tumor suppression.
- Uncontrollable Cell Division: The failure of tumor suppressor proteins to regulate the cell cycle may result in rapid and uncontrollable cell division, heightening the risk of tumor formation.
Step 2
Describe how this DNA could be screened for all known harmful mutations in both genes.
Answer
Screening for harmful mutations in BRCA1 and BRCA2 can be performed using several methods:
- Polymerase Chain Reaction (PCR): Starting with a saliva sample, PCR can amplify specific regions of the BRCA genes.
- Restriction Enzyme Digestion: The amplified DNA can be digested with specific restriction enzymes that cut the DNA at known mutation sites.
- Gel Electrophoresis: The resulting fragments are then separated using gel electrophoresis to distinguish normal from mutated sequences.
- Sequencing: Finally, DNA sequencing can identify specific mutations at the nucleotide level, enabling comprehensive screening for harmful genetic alterations.
Step 3
Suggest and explain how these drugs are an effective treatment of ER-positive breast cancers.
Answer
Drugs used in the treatment of ER-positive breast cancers are effective due to the following mechanisms:
- Binding to Oestrogen Receptors: These drugs can bind to the same oestrogen receptors in breast cancer cells, thereby preventing oestrogen from activating the cells and promoting growth.
- Inhibition of Tumor Growth: By competing with oestrogen for receptor binding, these drugs reduce the overall stimulation of growth pathways associated with oestrogen, effectively slowing or halting cancer progression.
Step 4
Explain why blood test results may not be conclusive when testing for prostate cancer.
Answer
Blood tests for prostate cancer can yield inconclusive results for several reasons:
- Variability of PSA Levels: Prostate-Specific Antigen (PSA) levels can be elevated due to non-cancerous conditions such as benign prostatic hyperplasia or prostatitis, leading to false positives.
- False Negatives: Conversely, not all prostate cancers produce elevated PSA levels, resulting in potential false negatives where cancer is present but undetected through blood tests.
Step 5
Suggest and explain how treatment with drugs might be able to reverse the epigenetic changes that cause cancers.
Answer
Drugs might reverse epigenetic changes and influence cancer progression through the following methods:
- Methylation Inhibitors: These drugs can inhibit enzymes responsible for DNA methylation, potentially reactivating suppressor genes that have been silenced in cancer cells.
- Histone Modifying Agents: Compounds that modify histones may restore the normal structure of chromatin, allowing genes controlling cell growth and differentiation to express appropriately again.
- Restoration of Gene Expression: By modifying the epigenetic landscape, these treatments can reinstate normal gene expression patterns, thereby inhibiting tumor growth.