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Investigating enzymes: temperature and pH
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You can measure how fast amylase digests starch, then change the temperature or the pH.
The method
Put drops of iodine in the dips of a spotting tile.
Mix starch solution and amylase in a test tube kept at a set temperature in a water bath.
Every 30 seconds, put a drop of the mixture into fresh iodine. When the iodine stays orange-brown, all the starch has been digested. Record the time.
Mix starch solution and amylase in a test tube kept at a set temperature in a water bath.
Every 30 seconds, put a drop of the mixture into fresh iodine. When the iodine stays orange-brown, all the starch has been digested. Record the time.
Changing temperature
Repeat at different temperatures, such as 20, 30, 40, 50 and 60 °C.
The shorter the time, the faster the rate. You can work out a rate as 1 ÷ time.
Rate rises up to the optimum, then falls as the active site changes shape and the enzyme is denatured.
The shorter the time, the faster the rate. You can work out a rate as 1 ÷ time.
Rate rises up to the optimum, then falls as the active site changes shape and the enzyme is denatured.
Changing pH (Biology only)
Keep the temperature the same and add buffer solutions to give different pH values.
Each enzyme has an optimum pH. Away from it, the active site changes shape, so the substrate no longer fits.
Control variables: volume and concentration of starch and amylase, and temperature (or pH, when temperature is the variable).
Each enzyme has an optimum pH. Away from it, the active site changes shape, so the substrate no longer fits.
Control variables: volume and concentration of starch and amylase, and temperature (or pH, when temperature is the variable).
At 40 °C all the starch was digested in 50 s. Work out the rate as 1 ÷ time.
- rate = 1 ÷ 50
- = 0.02
Answer: 0.02 per second
Time how long amylase takes to digest starch, testing samples with iodine on a spotting tile. Shorter time means faster rate (rate = 1 ÷ time). Change temperature with a water bath, or pH with buffers. Above the optimum, enzymes denature.
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