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Grade 10 Intermediate About 20 min Version 1 Awaiting review Premium

Enzymes: digesting starch with amylase

Digestion breaks large food molecules into small ones that can pass into the blood. Enzymes are proteins that speed up these reactions. Amylase, found in saliva and made by the pancreas, breaks starch down into sugar (maltose). Iodine solution turns blue-black when starch is present and stays orange-brown when there is none, so by testing drops of the mixture every minute you can see when all the starch has gone. Enzymes work best at an optimum temperature, which for human enzymes is about 37 °C, and at an optimum pH. High temperatures change the shape of the enzyme for good, so it stops working: it is denatured.

What you will learn

  • Use iodine to follow the digestion of starch.
  • Find the optimum temperature for amylase.
  • Explain the effects of temperature and pH on enzymes.

Before you start

  • Know that iodine is the test for starch.

Materials

  • Starch solution, amylase solution, iodine solution, buffer solutions

Equipment

  • Test tubes, water baths, spotting tile, droppers, thermometer, stopwatch

Procedure

  1. Mix starch solution and amylase at 37 °C and pH 7. Every minute, put a drop on iodine in a spotting tile, until the iodine stays orange-brown.
  2. Repeat at other temperatures from 10 °C to 80 °C and record the rate of digestion.
  3. Repeat at 37 °C in acid (pH 2) and in alkali (pH 9).

How this simulation is simplified

  • At 37 °C and pH 7, amylase digests 25% of the starch each minute; the rate falls away either side of 37 °C, and the enzyme is denatured at 70 °C and above.
  • In alkali (pH 9) the rate is 60% of that at pH 7; in acid (pH 2) it is 4%.