Enzymes Key Questions

Enzymes Key Questions

1. Enzyme- A protein or RNA that acts as a catalyst and so alters the speed of a biochemical reaction.

   • How does an enzyme speed up a reaction?- By lowering the activation energy of the reaction it catalyses.

2. What is the relationship between enzyme properties and protein structure?- Tertiary structure of its active site and the abilities to combine with complementary substrates to form an enzyme substrate complex.

3. Difference between the induced fit model and the lock and key model of enzyme action:

   • The induced fit model of enzyme action suggests/proposes that the active site of the enzymes forms as the enzyme and substrate interact.
   • The lock and key model proposes that the active site is rigid and has a specific structure that is complementary to a substrate further suggesting that the active site does not change shape.
     • Enzymes are specific because they are globular proteins that have a specific 3D shape due to their primary structure.

4. What is the effect of enzyme concentration on an enzyme controlled reaction?- Enzymes are not used up in an enzyme controlled reaction because there is not enough substrate therefore they work efficiently at very low concentrations.

   • What is the effect of substrate concentration on an enzyme controlled reaction? Concentration of enzyme is fixed and the substrate concentration is slowly increased. The rate of reaction increases until there is an excess amount of substrate so the graph would level off.
   • Effect of pH: An increase or decrease in pH away from the optimum reduces the rate of enzyme action. If the pH is beyond a certain pH, the enzyme becomes denatured.
     • How the change in pH affects the enzyme: Alters the charges on the amino acids that make up the active site of the enzyme. As a result the substrate can no longer become attached to the active site so enzyme-substrate complexes cannot be formed.
       • Effect of temperature on an enzyme-controlled reaction? Increases the kinetic energy of the molecules meaning more collisions, more enzyme substrate complexes are formed which increases the rate of reaction.
       • Denaturing as a result of temperature: Rise in temperature causes hydrogen bonds to break results in the enzyme and active site changing shape.
         • Effect of denaturation on the rate of reaction: The substrate fits less easily into the changed active site which slows the rate of reaction.

5. Why is the optimum temperature for our bodies 37.C not 40.C? Higher temps would increase our metabolic rate however additional energy would be needed to maintain high temperatures. Other proteins may be denatured at higher temperatures.

6. Competitive inhibitor- they have a molecular shape similar to the substrate which allows them to occupy the active site complementary to a substrate so therefore competes with substrate molecules for available active sites.

   • Effect on a enzyme-controlled reaction: The greater concentration of the inhibitor the less effective the enzyme will be.
   • Non-competitive inhibitor- They attach themselves to the enzyme at a binding site other than the active site.
     • Effect on an enzyme-controlled reaction: An increase in substrate concentration does not increase the effect of the inhibitor.