5 - Enzymes

• What is the method for this practical? (part 1)

  1. On a tile, label each well with the time (from 0 onwards) and add a drop of iodine solution to each well.
  2. Add 2 cm^3 of each buffer solution using a syringe (ranging from pH 3.0 to 7.0) into each labelled test tube.
  3. Immerse the starch solution, amylase solution, and the test tubes of buffer solution in a water bath at 25°C.
  4. Allow a few minutes for the temperature to equilibrate.
  5. Use a syringe to add 2 cm^3 of amylase into a test tube of buffer solution.
• What is the method for this practical? (part 2)

  6. Use a syringe to add 2 cm^3 of starch into the same test tube and start timing immediately.

  7. Use the glass rod to transfer a drop of the mixture to the well labelled '0' on the tile.

  8. Repeat step 6 every 30 seconds, rinsing the glass rod in between every test, until the iodine solution remains brown and doesn’t turn blue-black.

  9. Calculate the rate of enzyme reaction by using 1 / time taken for iodine solution to remain brown.

  10. Repeat steps 2-8.

  11. Plot a graph of the rate of enzyme reaction against pH.
• Potential hazards:

  Be careful using hot water.

  If using a Bunsen burner tie long hair back and wear goggles.
• What is a buffer solution?

  A solution which can resist changes in pH.