Turn over 5 2 Acetylcholinesterase is an enzyme involved in regulating the transmission of nerve impulses across some synapses. (a) Acetylcholinesterase is found on the cell surface membranes of neurones and red blood cells. These acetylcholinesterase molecules have different primary structures. In humans, a single gene codes for acetylcholinesterase. (i) Explain how a single gene can give rise to acetylcholinesterase molecules with different primary structures. 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(ii) Explain how the acetylcholinesterase gene can be expressed in some tissues but not others. 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It has been suggested that inhibitors of acetylcholinesterase may be useful in the treatment of Alzheimer’s disease. (i) Explain why inhibitors of acetylcholinesterase could be useful in the treatment of Alzheimer’s disease. 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Turn over 7 (ii) Trials of a new inhibitor were carried out using tissue cultures. The effect of the concentration of the inhibitor on acetylcholinesterase activity and cell viability was measured. Percentage cell viability was measured as the percentage of cells that were not killed by the inhibitor. The graph shows the results for this inhibitor. Acetylcholinesterase activity / a.u. Percentage cell viability (%) Concentration of inhibitor / µmol dm−3 Key Cell viability Acetylcholinesterase activity 4 3 2 1 0 250 200 0 50 150 100 100 75 50 25 0 State and justify a suitable concentration of inhibitor to use in clinical trials. 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(Total for Question 2 = 11 marks)