Enzymes

• How do enzymes increase the rate of reaction

  Enzyme lower the activation energy for a reaction
• Explain how the formation of the enzyme substrate complex causes a high rate of reaction

  The substrate fits into the complimentary active site and makes temporary bonds. There is a slight change in the shape of the active site, placing strain on the bonds in the substrate.

  This lowers the activation energy for the reaction and increases the rate of reaction.
• why can a small quantity of enzyme be effective

  Enzymes do not get used up in the reaction, and can be reused.
• why can changing an amino acid in the active site prevent the enzyme from functioning

  The sequence of amino acid changes the 3-D tertiary of the active site so that it no longer binds to the substrate.
• Why do enzymes only work with one substrate

  The actives sites are different specific shapes, the 3-D tertiary structure of the active site is complimentary to only one substrate, so different enzyme-substrate complexes are formed.
• Describe and explain how non competitive enzyme inhibitors affect the rate of enzyme controlled reaction

  The inhibitor binds to a site other than the active site, this changes the shape of the active site, preventing the formation of enzyme-substrate complexes, lowering the rate of reaction. This cannot be overcome by adding more substrate.
• Describe and explain how competitive enzyme inhibitors affect the rate of enzyme controlled reaction

  The inhibitor is a similar shape to the substrate

  (complimentary to the active site), it binds to the active site of the enzyme preventing enzyme-substrate complexes forming.

  Adding more substrate can overcome the inhibition.
• Explain how enzymes allow reactions to take place at body temperature

  Enzymes are catalysts they lower the activation energy for a reaction by forming enzyme-substrate complexes.
• Explain why pH affects enzyme function

  Enzymes have an optimum pH where they work best. Away from the optimum pH the enzymes H-bonds and ionic bonds are changed, changing the shape of the active site, preventing enzyme-substrate complexes from forming. The enzyme is denatured.
• Describe the biochemical test for an enzyme

  Add biurets reagent to the test solution. A positive result is from blue to purple
• Explain why temperature affects enzyme function

  High temperatures have more kinetic energy; Breaks hydrogen/ionic bonds in the 3-D tertiary structure; changing the shape of the active site, it's no longer complimentary to the substrate so fewer enzyme-substrate complexes are formed;
• Suggest an advantage of a bacterium secreting extracellular proteases

  To digest/hydrolyse proteins into amino acids; amino acids can then be absorbed for making proteins for growth/reproduction;
• suggest why some enzyme catalysed reactions will only occur if the substrate has been phosphorylated

  Phosphorylation makes the substrate more reactive/lowers the activation energy for the reaction.
• Explain why low temperature affects enzyme function

  Temperatures lower than the optimum means enzyme and substrate have less kinetic energy; therefore the enzyme and substrate will collide less often with the sufficient energy for the reaction to take place, fewer enzyme substrate complexes. Lower rate of reaction.
• What are the control variables for enzyme substrate investigations

  Concentration of enzyme; concentration of substrate; volume of enzyme; volume of substrate; temperature; pH; concentration/volume inhibitor;
• What is a suitable control investigation for enzyme substrate investigations

  All the same conditions, but use a boiled (denatured) enzyme solution.
• Describe and explain the shape of a normal substrate concentration vs rate of reaction graph for an enzyme controlled reaction

  There is an initial increase because more enzyme-substrate complexes are formed; Then it will level off as there will be no free enzyme active sites, as the enzyme is the limiting factor.
• Explain why a mutation in the code for an enzyme may affect its function

  The mutation may code for a different amino acid at the active site of the enzyme; this will lead to a structural difference due to a change in the ionic/hydrogen bonds or disulphide bridge between the R-groups of the amino acids; the active site is no longer complimentary to the substrate; so fewer enzyme-substrate complexes will form.
• Explain why a mutation in the code for an enzyme may not affect its function

  The mutation may be for a substitution that codes for the same amino acid (the code is degenerate), this will therefore

  not change the structure of the enzyme's active site.