3.3.13.3 Enzymes Quiz: AQA Chemistry, Unit 3

The 20 questions

1. What type of molecule is an enzyme?

   • A carbohydrate that stores energy
   • A protein that acts as a biological catalyst
   • A nucleotide that carries genetic information
   • A lipid that forms cell membranes

2. What is the active site of an enzyme?

   • The part of the enzyme that is always a metal ion
   • The end of the protein chain with the carboxylic acid group
   • The region where the substrate binds and the reaction occurs
   • The region where the enzyme is made in the cell

3. Why does an enzyme bind only one enantiomer of a substrate?

   • Enzymes are destroyed by any enantiomer present, so the reaction stops at once
   • Enzymes can only bind molecules with a benzene ring in their structure at all
   • Enzymes react with both enantiomers equally, so the chirality of the substrate is ignored
   • The active site is a three-dimensional shape that is complementary to only one enantiomer

4. How does a competitive inhibitor drug work?

   • It changes the enzyme into a non-protein molecule
   • It destroys the substrate molecule in the blood
   • It blocks the active site so the substrate cannot bind
   • It increases the rate of the enzyme-catalysed reaction

5. How are computers used in the design of enzyme inhibitor drugs?

   • They measure the boiling point of the enzyme, which indicates its active site shape
   • They model the active site shape to predict which molecules will fit
   • They synthesise the drug without any chemistry, which saves time and reagents
   • They replace the need for any laboratory testing of the candidate drug molecules

6. Which model describes how a substrate fits an enzyme's active site?

   • Ideal gas model
   • Plum pudding model
   • Valence shell model
   • Lock and key model

7. How does an enzyme increase the rate of a reaction?

   • It lowers the activation energy of the reaction
   • It increases the temperature of the reaction mixture
   • It raises the equilibrium constant of the reaction
   • It is used up in the reaction and changes its composition

8. Why might one enantiomer of a drug be active while its mirror image is inactive?

   • Only one enantiomer fits the chiral active site properly
   • Both enantiomers are identical in 3D shape
   • The active enantiomer contains a double bond only
   • The inactive enantiomer has more carbon atoms

9. Why does a drug that is a racemic mixture often have lower effectiveness than a pure enantiomer?

   • Racemic mixtures contain no carbon atoms
   • The racemic mixture always destroys the enzyme
   • Only one enantiomer binds the active site, so half of the drug is inactive
   • The second enantiomer makes the drug react faster than the first

10. Why is an enzyme's activity affected by temperature beyond an optimum?

    • Heat converts the enzyme into a substrate
    • Heat removes all carbon-carbon bonds from the substrate
    • Heat makes the enzyme bind to the substrate more tightly
    • Heat denatures the protein, changing the shape of the active site

11. Which structural level of a protein forms the active site of an enzyme?

    • Tertiary structure
    • Secondary structure only
    • Primary structure only
    • Quaternary structure always

12. Competitive inhibition can be overcome by which change?

    • Removing the enzyme from the solution
    • Increasing the substrate concentration
    • Lowering the temperature to zero
    • Adding more inhibitor molecules only

13. What is the purpose of a drug that blocks an enzyme's active site?

    • To prevent the enzyme from catalysing its normal reaction
    • To make the substrate more stable so it resists being broken down by the enzyme
    • To change the enzyme into a different protein that catalyses a new reaction
    • To increase the rate of the enzyme reaction by binding the substrate more tightly

14. Why must a drug fit an enzyme's active site precisely?

    • Intermolecular bonds such as hydrogen bonds and ionic attractions hold the drug in place
    • The drug must be a metal salt to fit into the enzyme and bind to its surface
    • The drug must be larger than the enzyme so that it can cover the whole active site
    • The drug has to have a double bond to bind to the active site of the enzyme

15. Which statement about enzyme catalysis is correct?

    • Enzymes are consumed in each catalysed reaction
    • Enzymes are not used up in the reaction they catalyse
    • Enzymes always increase the equilibrium yield
    • Enzymes are non-protein catalysts made of metals

16. Which two features of an active site ensure substrate specificity?

    • Colour and molar mass of the substrate
    • Number of carbon atoms in the substrate
    • Shape and charge complementarity to the substrate
    • Melting point and density of the substrate

17. What is a stereospecific active site?

    • One that is found only in aromatic compounds
    • One that binds only one stereoisomer of a substrate
    • One that contains a triple bond
    • One that binds all isomers of a molecule equally

18. Why do chemists use computers to design drugs for enzymes?

    • To measure the pH of the enzyme solution directly, which is needed for the design
    • To predict whether a candidate molecule will fit the active site
    • To show the enzyme is a carbohydrate, which is a question of structure and not design
    • To remove the need to synthesise compounds, because the computer can make them

19. What is the effect of pH on an enzyme beyond its optimum?

    • The enzyme changes into a sugar, which is then unable to bind the substrate at all
    • The enzyme gains extra peptide links, which make the active site stronger and more rigid
    • The enzyme becomes more reactive towards any substrate, which increases its activity
    • Ionic and hydrogen bonds in the active site are disrupted, reducing activity

20. Which statement describes an enzyme inhibitor drug that blocks the active site?

    • It binds to the substrate and removes its carbon atoms
    • It increases the number of active sites on the enzyme
    • It makes the substrate react with water only
    • It stops the natural substrate from fitting into the active site

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