Core practical: pH and enzyme activity

Temperature: rate rises up to the optimum, then falls quickly as the enzyme is denatured.
pH: each enzyme has an optimum pH. Away from it, the active site changes shape.
Substrate concentration: the rate rises as more substrate is added, then levels off when all the active sites are busy at the same time.

1. Put one drop of iodine solution into each dip of a spotting tile.
2. Put amylase solution and a buffer solution (to fix the pH) in a test tube in a water bath at a set temperature, for example 35 °C.
3. Add starch solution, mix and start the stopwatch.
4. Every 10 seconds, put a drop of the mixture into the next dip of iodine.
5. When the iodine stays orange-brown, all the starch has been broken down. Record the time.
6. Repeat with buffers of different pH. Keep the temperature, volumes and concentrations the same.

rate = 1 ÷ time (for example, starch gone in 50 s gives 1 ÷ 50 = 0.02 s^-1). If an amount is measured: rate = amount of product ÷ time.
Enzymes break down large molecules: carbohydrates into sugars, proteins into amino acids, lipids into fatty acids and glycerol.
Enzymes also synthesise (build) large molecules: sugars into starch, glycogen and cellulose; amino acids into proteins; fatty acids and glycerol into lipids.