Enzymes

Enzymes

Enzymes are biological catalysts: they speed up reactions and are not used up. Each one has an active site that fits one type of molecule, like a key in a lock.

Human enzymes work best at about 37 °C. Too hot and the active site changes shape: the enzyme is denatured and stops working.

The amylase practical

1. Put starch solution and amylase, in separate tubes, into water baths at different temperatures (for example 20, 37 and 80 °C) for a few minutes, so each starts at the right temperature.
2. Put a drop of iodine in each well of a spotting tile.
3. Add the amylase to the starch at each temperature and start the stopwatch. Set up a control tube of starch and water with no amylase.
4. Every 30 seconds, add a drop from each tube to a fresh well of iodine.
5. Record the time when the iodine stays orange-brown: the starch has gone.

Results: fastest at 37 °C, slower at 20 °C, and the starch never goes at 80 °C (denatured). The control stays blue-black, which shows it is the amylase that breaks down the starch. Fair test: only the temperature changes.

The temperature is the independent variable (what you change); the time for the starch to go is the dependent variable (what you measure). Repeat the experiment and check your results agree: that makes them more reliable.