Temperature and enzyme activity

Explanation

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

At low temperature, enzyme and substrate molecules have little kinetic energy and move slowly. They collide less often, so fewer enzyme-substrate complexes form per unit time. As temperature rises, the molecules gain kinetic energy and move faster. The frequency of effective collisions increases, so the rate of reaction increases.

An enzyme has an optimum temperature at which its activity is greatest under the conditions tested. Beyond it, heat breaks the bonds that hold the enzyme in its 3D shape. The 3D shape of the active site changes, so the substrate is no longer complementary to it and cannot bind. The enzyme is denatured, fewer enzyme-substrate complexes form and the rate falls. The optimum is not the same for every enzyme.

Cold usually reduces activity without permanently changing the active site. Warming a cold enzyme appropriately can restore a higher rate. Heating a denatured enzyme and then cooling it does not usually restore its original function. Avoid saying that an enzyme is alive and can die.

To investigate temperature with amylase and starch, use water baths to bring enzyme and substrate separately to the chosen temperature before mixing. Keep pH, concentrations and volumes constant. At regular intervals, test a small drop of reaction mixture with iodine on a spotting tile. The endpoint is the first test where starch is no longer detected.

Use the same sampling interval and endpoint rule for every temperature, repeat each condition and compare means. If the same amount of starch is digested, 1/time is a relative measure of rate. An endpoint time is less precise when sampling intervals are long; shorter regular intervals improve the estimate.