Enzyme Investigations (Cambridge (CIE) O Level Biology): Revision Note

The progress of enzyme-catalysed reactions can be investigated by:

• Measuring the rate of formation of a product 

• Measuring the rate of disappearance of a substrate

For example, the enzyme catalase releases oxygen gas as a product as it breaks down the substrate hydrogen peroxide 

• The oxygen gas can be collected and the volume is measured using a measuring cylinder or a gas syringe

Starch solution is heated to a set temperature

Iodine is added to wells of a spotting tile

Amylase is added to the starch solution and mixed well

Every minute, droplets of solution are added to a new well of iodine solution

This is continued until the iodine stops turning blue-black (this means there is no more starch left in the solution as the amylase has broken it all down)

Time taken for the reaction to be completed is recorded

Experiment is repeated at different temperatures

The quicker the reaction is completed, the faster the enzyme is working

Place single drops of iodine solution in rows on the tile

Label a test tube with the pH to be tested

Use the syringe to place 2cm³ of amylase in the test tube

Add 1cm³ of buffer solution to the test tube using a syringe

Use another test tube to add 2cm³ of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette

After 10 seconds, use a pipette to place one drop of mixture on the first drop of iodine, which should turn blue-black

Wait another 10 seconds and place another drop of mixture  on the second drop of iodine

Repeat every 10 seconds until iodine solution remains orange-brown

Repeat experiment at different pH values - the less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH