investigating the enzyme amylase

Amylase catalyses the breakdown of starch into sugar. How is the activity of this enzyme affected by temperature? You can start to find out by monitoring the activity at different temperatures.

You use Iodine as an indicator to show when the starch has been broken down. The iodine changes from a blue-black to almost colourless. A light sensor can be used, like a colorimeter, to monitor this colour change.

What you need: Fresh amylase and starch solutions, iodine, distilled water, a sheet of black paper, light sensor. Reaction container such as a small beaker, Perspex box or a plastic indicator paper box.

Setting up

Set up the light sensor and reaction container. Add a known amount of starch solution and 2-3 drops of iodine.
Use black paper to shield the beaker from changes in the light level. Try not to completely cover the chemicals – it helps if you can see the colour change. Connect the light sensor to a socket on the interface.
Start the computer software. Start recording and look for a trace on screen. If the light sensor is adjustable, change its range to get the trace on screen.

Recording the data

Add amylase to the beaker. (Typically you add 2 cm3 amylase to 10 cm3 starch solution). Set-up the software to record for 15 minutes. When the reaction is complete, record the temperature and save the results. Replace the solutions. Make a new recording using starch at a different temperature.

Questions about your results

• What happens to the appearance of the solution during the reaction?
• When was the reaction working at its fastest?
• How does the graph tell you what is happening in the reaction?
• How does temperature affect the graph?
• Calculate the average gradient of each graph to measure the reaction rate. You will need to select a part of each graph – which part did you choose? What do these results tell you?