Temperature and enzyme activity

Explanation

Enzymes only work in solution. The enzyme and its substrate must be dissolved in water so that they can move and collide. An effective collision is one where the substrate enters the active site and an enzyme-substrate complex forms.

At a low temperature, the molecules have little kinetic energy and move slowly. They collide less often, so fewer enzyme-substrate complexes form. As the temperature rises, the molecules gain kinetic energy and move faster. Effective collisions happen more often, so the rate of reaction increases.

Each enzyme has an optimum temperature, where it works fastest. Above the optimum, heat breaks the bonds that hold the enzyme in its 3D shape. The shape of the active site changes, so the substrate no longer fits. The enzyme is denatured, and the rate falls.

Cold slows an enzyme down but does not usually damage its active site. If you warm it up again, it works faster again. But once an enzyme has been denatured by heat, cooling it does not usually fix it.

To test the effect of temperature on amylase, put the amylase and the starch in separate tubes in a water bath until they reach the temperature you want. Then mix them. Keep the pH and the amounts the same. Every so often, put a drop of the mixture on a spotting tile with iodine. The end point is the first drop where the iodine does not turn blue-black.

Use the same timing and the same end point at every temperature. Repeat each temperature and work out a mean. Testing drops more often gives a more accurate end point.