Enzymes

• What’s the aim of this practical?

  to investigate the effect of pH on the rate of reaction of amylase
• What will you do in this experiment?

  • Use the enzyme amylase to breakdown starch at a range of pH values, using iodine solution as an indicator for the reaction occurring
  • Use a continuous sampling technique to monitor the progress of the reaction
  • Amylase is an enzyme that digests starch (a polysaccharide of glucose)into maltose (a disaccharide of glucose)
  • Starch can be tested for easily using iodine solution
• What is the first step in the method described?

  Place single drops of iodine solution in rows
• What should be labeled on the test tube?

  The pH to be tested
• How much amylase should be placed in the test tube?

  2cm³ of amylase
• What is added to the test tube after amylase?

  1cm³ of pH buffer solution
• What should be done after adding starch solution to the test tube?

  Start the stopwatch while mixing
• What color should the iodine turn when a drop of the mixture is added?

  Blue-black
• How often should a drop of the mixture be placed on the iodine?

  Every 10 seconds
• What indicates that all the starch has been digested?

  The iodine solution remains orange-brown
• What does a quicker change to orange-brown indicate about the enzyme's effectiveness?

  The enzyme works better at that pH
• What should be done to test different pH values?

  Repeat the experiment at different pH values
• What are some adjustments to the method?

  • The above method can be adapted to control temperature by using a water bath at 35°C
  • All solutions that need to be used (starch, amylase, pH buffers) should be placed in a water bath and allowed to reach the temperature (using a thermometer to check) before being used
  • A colorimeter can be used to measure the progress of the reaction more accurately; with a solution containing starch being darker and glucose light (as a result of the colour-change of iodine) – this will affect the absorbance or transmission of light in a colorimeter