Required Practical 1

• Give examples of variables that could affect the rate of an enzyme controlled reaction

  • Enzyme concentration/volume
  • Substrate concentration/volume
  • Temperature of solution
  • pH of solution
  • Inhibitor concentration
• Describe how temperature can be controlled:

  • Use a thermostatically controlled water bath
  • Monitor using a thermometer at regular intervals and add hot/cold water if temperature fluctuates
• Describe how pH can be controlled:

  • Use a buffer solution
  • Monitor using a pH meter at regular intervals
• Why are the enzyme and substrate solutions left in the water bath for 10 minutes before mixing?

  So solutions could equilibrate/reach the temperature of the water bath
• Describe a control experiment:

  • Use denatured enzymes
  • Everything else the same as the experiment
• Describe how the rate of an enzyme-controlled reaction can be measured:

  1)Measure time taken for reaction to reach a set point e.g. concentration/volume/colour of substrate/mass

  • Rate of reaction = 1/time; e.g. units = s-1

  2)Measure concentration/volume/mass etc at regular intervals throughout the reaction

  • Plot on a graph with time on x axis and whatever is being measured on the y axis
  • Draw a tangent at t = 0 (or any other time for rate at a particular point)
  • Initial rate of reaction = Change in y/change in x; e.g. units = cm3s-1
• Suggest a safety risk and explain how to reduce this risk:

  • Handling enzymes may cause an allergic reaction
  • Avoid contact with skin by wearing gloves and eye protection
• Explain why using a colorimeter to measure colour change is better than comparison to colour standards:

  • Not subjective
  • More accurate
• Explain a procedure that can be used to stop each reaction:

  • Boil/add strong acid or alkali to denature enzyme
  • Put in ice = lower kinetic energy so no E-S complexes form
  • Add high concentration of inhibitor so no E-S complexes form
• Explain why the rate of reaction decreases over time throughout each experiment:

  • Initial rate is highest as substrate concentration not limiting/many E-S complexes form
  • Reaction slows as substrate used up and often stops as there is no substrate left