You will investigate the breakdown of starch by amylase at different pHs.
The different pHs under investigation will be produced using buffer solutions. Buffer solutions produce a particular pH, and will maintain it if other substances are added.
The amylase will break down the starch.
A series of test tubes containing a mixture of starch and amylase is set up at different pHs.
A sample is removed from the test tubes every 10 seconds to test for the presence of starch. Iodine solution will turn a blue/black colour when starch is present, so when all the starch is broken down, a blue-black colour is no longer produced. The iodine solution will remain orange-brown.
A control experiment must be set up – without the amylase – to make sure that the starch would not break down anyway. The result of the control experiment must be negative – the colour must remain blue-black – for results with the enzyme to be valid.
When the starch solution is added:
This is how you might set up the experiment:
For each pH investigated, record the time taken for the disappearance of starch, ie when the iodine solution in the spotting tile remains orange-brown.
|pH||Time taken for the disappearance of starch in s|
The time taken for the disappearance of starch is not the rate of reaction.
It will give us an indication of the rate, but is the inverse of the rate – the shorter the time taken, the greater the rate of the reaction.
We can calculate the rate of the reaction by calculating 1/t, obtaining a measure of the rate of reaction by dividing one by the time taken for the reaction to occur.
So, from the results:
|pH||Time taken for the disappearance of starch in s||Rate of breakdown of starch (1/t)|
Plot a graph of rate of reaction against pH.
A similar experiment can be carried out to investigate the effect of temperature on amylase activity.
Set up a series of test tubes in the same way and maintain these at different temperatures using a water bath – either electrical or a heated beaker of water.
Depending on the chemical reaction under investigation, you might monitor the reaction in a different way. If investigating the effect of temperature on the breakdown of lipid by lipase, for instance, you could monitor pH change – lipids are broken down into fatty acids and glycerol. As the reaction proceeded, the release of fatty acids would mean that the pH would decrease.