Recall questions 2

• Describe the induced fit model of enzyme action

  • (before the reaction) active site not complementary to substrate
  • Active site changes shape as the substrate binds, so the active site becomes complementary to the substrate
  • So an enzyme-substrate complex can form
  • This stresses / distorts bonds in the substrate, leading to a reaction
• Explain how the shape of an enzyme molecule is related to its function.

  • Enzymes have a specific tertiary structure/ shape
  • The active site is a complementary shape to the substrate
  • Therefore the substrate can bind to the active site
• Explain why enzymes only act on one substrate

  • Active site complementary/ specific structure/ shape
  • Only fits/ binds to one substrate
  • Forms enzyme-substrate complexes
• Explain how temperature affects rate of reaction  

  • As the temperature increases, the rate of reaction increases
  • Enzymes and substrates have more kinetic energy
  • So there are more collisions
  • More enzyme-substrate complexes form
  • If temperature exceeds the optimum, rate of reaction decreases
  • Hydrogen bonds break
  • Tertiary structure changes
  • Shape of active site changes
  • No enzyme-substrate complexes can form
• Explain how decreasing temperature can affect an enzyme reaction

  • Lower temperature means less kinetic energy
  • Fewer collisions between enzyme and substrate
  • Fewer enzyme-substrate complexes formed
• Explain how increasing temperature above the optimum affects an enzyme’s activity.

  1. Enzyme denatured / hydrogen bonds/ bonds holding the tertiary structure broken / tertiary structure changed
  2. Change in shape of active site
  3. Substrate/ protein no longer fits/ binds into active site / few or no enzyme-substrate complexes
• Explain how dramatically decreasing the pH affects enzyme activity

  1. A decrease in pH increases the concentration of H+ ions
  2. This changes the charges of amino acids
  3. So hydrogen and ionic bonds are disrupted
  4. So the tertiary structure of enzyme changes / the enzyme is denatured
  5. So the shape/ charge of the active site is changed
  6. Therefore enzyme-substrate complexes can no longer form
  7. So rate of enzyme activity decreases
• Explain how substrate concentration affects the rate of reaction

  • As substrate concentration increases, the rate of reaction increases
  • Because the substrate concentration is the limiting factor
  • As substrate concentration increases further, the rate of reaction stays constant
  • Because all the active sites are occupied
  • The number of enzymes is the limiting factor
• Explain how enzyme concentration affects the rate of reaction

  • As enzyme concentration increases, the rate of reaction increases
  • Because enzyme concentration is the limiting factor
  • As enzyme concentration increases further, the rate of reaction stays constant
  • Because the amount of substrate is the limiting factor
  • Or the temperature is not high enough for the reaction to happen any faster
• Use your knowledge of protein structure to explain why enzymes are specific and may be affected by non-competitive inhibitors.

  • Each enzyme has a specific primary structure/ amino acid sequence
  • So it folds in a particular way/ has a particular tertiary structure
  • This forms an active site with a unique shape/ structure
  • The shape of the active site is only complementary to one specific substrate
  • A non-competitive inhibitor binds to a site on the enzyme other than the active site
  • This changes the shape of the active site
  • So no more enzyme-substrate complexes can form
• Describe how competitive and non-competitive inhibitors can limit enzyme activity

  Competitive:

  • inhibitor is a SIMILAR shape to the substrate
  • inhibitor is complementary to the ACTIVE SITE
  • so inhibitor binds to the active site
  • so fewer enzyme-substrate complexes form
• Describe how competitive and non-competitive inhibitors can limit enzyme activity

  Non-competitive:

  • inhibitor is complementary to the ALLOSTERIC SITE on the enzyme
  • so inhibitor binds with the allosteric site
  • so the shape of the active site changes
  • so the active site is no longer complementary to the substrate
  • so fewer enzyme-substrate complexes are formed
• In humans, the enzyme maltase breaks down maltose to glucose.
This takes place at normal body temperature. Explain why maltase:​

  •        only breaks down maltose​

  •        allows this reaction to take place at normal body temperature 

  1. Tertiary structure/ 3D shape of enzyme (means)
  2. Active site complementary to maltose
  3. Description of induced fit
  4. Enzyme is a catalyst/ lowers activation energy/ energy required for reaction
  5. By forming enzyme-substrate complex (binding stresses the bonds so more easily broken)