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Guillain–Barré syndrome is a rare disease in which the immune system damages the myelin sheath of neurones - AQA - A-Level Biology - Question 10 - 2019 - Paper 1
Question 10
Guillain–Barré syndrome is a rare disease in which the immune system damages the myelin sheath of neurones. Myelin sheath damage can cause a range of symptoms, for e... show full transcript
Worked Solution & Example Answer:Guillain–Barré syndrome is a rare disease in which the immune system damages the myelin sheath of neurones - AQA - A-Level Biology - Question 10 - 2019 - Paper 1
Step 1
Damage to the myelin sheath of neurones can cause muscular paralysis (lines 2-4). Explain how.
Answer
The damage to the myelin sheath impairs the transmission of nerve impulses along the axons of the neurones. This disruption can significantly decrease signal speed or prevent signals from reaching muscles altogether, resulting in muscular paralysis.
Step 2
Sometimes Guillain–Barré syndrome causes heart rate irregularities (lines 4–5). Suggest and explain why.
Answer
Guillain–Barré syndrome can affect the autonomic nervous system, which regulates involuntary actions including heart rate. Damage to the myelin sheath can interfere with nerve signals that control heart rate, leading to irregularities.
Step 3
The first successful drug trial to reduce concentrations of huntingtin in the brain used single-stranded DNA molecules (lines 13–14). Suggest and explain how this drug could cause a reduction in the concentration of the protein huntingtin.
Answer
The single-stranded DNA molecules can bind to the mRNA responsible for producing huntingtin. By binding to the mRNA, this drug can prevent translation from occurring, thus reducing the levels of huntingtin protein produced in the brain.
Step 4
Scientists from the first successful drug trial to reduce concentrations of huntingtin (lines 9–11) reported that the drug is not a cure for Huntington's disease. Suggest two reasons why the drug should not be considered a cure. Do not include repeats of the drug trial in your answer.
Answer
- The drug targets only the concentration of huntingtin protein and does not address the underlying genetic mutation responsible for the disease.
- Even with reduced huntingtin levels, the brain may already have sustained irreversible damage from the disease, leading to continued symptoms.
Step 5
Suggest two reasons why people had the drug injected into the cerebrospinal fluid (lines 12–13) rather than taking a pill containing the drug.
Answer
- Injecting the drug directly into the cerebrospinal fluid allows for faster and more effective delivery to the brain compared to oral administration.
- The drug may be sensitive to digestion or enzymes in the digestive tract, which could degrade its effectiveness if taken as a pill.
Step 6
Suggest and explain one way epigenetics may affect the age when symptoms of Huntington's disease start.
Answer
Epigenetic modifications, such as methylation, can influence gene expression without altering the DNA sequence. Changes in the epigenetic regulation of the gene responsible for Huntington's disease might delay or hasten the onset of symptoms by affecting the level of mutant huntingtin protein produced.