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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
Guillain–Barré syndrome leads to damage of the myelin sheath surrounding neurones. This results in disrupted nerve conduction, which affects the transmission of electrical impulses. Motor neurones that supply muscles may fail to transmit signals effectively, causing muscular paralysis due to a lack of motor neuron stimulation.
Step 2
Sometimes Guillain–Barré syndrome causes heart rate irregularities (lines 4–5). Suggest and explain why.
Answer
The syndrome affects autonomic neurones that regulate involuntary functions, including heartbeat. Damage to these neurones can lead to irregular heart rhythms, as the signals that guide heart rate may become erratic or cease entirely due to the compromised nerve impulse transmission.
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
Single-stranded DNA molecules can bind to the mRNA of the huntingtin protein, forming a complementary pair. This binding prevents the mRNA from being translated into the huntingtin protein, ultimately leading to a reduction in its concentration. By inhibiting mRNA, the drug reduces the production of the harmful protein.
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
First, the drug only reduces the production of huntingtin but does not address the underlying genetic mutation causing Huntington’s disease. Second, the brain damage caused by the disease may already be irreversible, meaning that while the drug can reduce levels of the protein, it cannot restore the functionality of the damaged neural circuits.
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 into the cerebrospinal fluid ensures direct delivery to the brain, bypassing barriers that may hinder efficacy if taken orally. Additionally, this method allows for more rapid onset of action, as the drug can reach its target more quickly compared to absorption through the digestive system.
Step 6
Explain and explain one way epigenetics may affect the age when symptoms of Huntington’s disease start.
Answer
Epigenetics involves changes in gene expression without altering the DNA sequence. Methylation of certain genes or regulatory regions may suppress or activate the expression of the huntingtin gene, potentially influencing the onset of symptoms. If epigenetic factors increase the expression of the mutated gene, symptoms may appear earlier, whereas protective epigenetic modifications could delay symptom onset.