EnzymesAQA A-Level Chemistry: Subtopic test

1. 1
   Enzymes speed up the chemical reactions in living cells. An enzyme binds a substrate molecule at its active site, and the substrate is then converted into products.

   (a)

   Which statement about enzymes is correct?

   [1 mark]

   • AThey are proteins that act as biological catalysts
   • BThey are carbohydrates that supply energy
   • CThey are lipids that store energy
   • DThey are nucleic acids that carry genetic information

   (b)

   How does an enzyme increase the rate of a reaction?

   [1 mark]

   • ABy increasing the activation energy
   • BBy providing an alternative route with a lower activation energy
   • CBy being used up in the reaction
   • DBy shifting the equilibrium towards the products

   (c)

   Explain what is meant by the term stereospecific active site.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A drug is being developed to treat a bacterial infection. It is designed to inhibit an enzyme that the bacterium needs to survive, and its shape is similar to that of the enzyme's substrate.

   (a)

   How does the drug act as an enzyme inhibitor?

   [1 mark]

   • AIt hydrolyses the enzyme into amino acids
   • BIt reacts with the product to remove it
   • CIt binds to the active site and blocks it so that the substrate cannot bind
   • DIt supplies extra substrate to the enzyme

   (b)

   Why is computer modelling useful in designing this drug?

   [1 mark]

   • AIt removes the need for any clinical trials
   • BIt makes the enzyme change shape to fit the drug
   • CIt can synthesise the drug without using chemicals
   • DIt can predict how well candidate molecules fit the active site before they are made

   (c)

   Suggest why the drug needs a shape similar to that of the substrate.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Lactic acid, CH₃CH(OH)COOH, exists as two enantiomers. An enzyme in muscle tissue acts on only one of them.

   (a)

   Explain why the enzyme can bond to only one enantiomer of lactic acid.

   [3 marks]

   (b)

   A drug that inhibits an enzyme is made as a mixture containing equal amounts of two enantiomers. Only one enantiomer binds to the active site. Suggest the consequences of using the mixture rather than the single active enantiomer.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A pharmaceutical company is designing an inhibitor for an enzyme involved in a disease. The enzyme is a protein with a stereospecific active site, and the company is using computer modelling to design candidate drug molecules.

   (a)

   Explain how enzymes act as catalysts and how a drug can act as an enzyme inhibitor.

   [6 marks]

   (b)

   Discuss how computer modelling helps in the design of the drug, and explain why the company should make the drug as a single enantiomer.

   [6 marks]

   Total for question 4: 12 marks

End of questions