Effect of temperature and pH on amylase

Objectives

• Follow the digestion of starch with iodine.
• Investigate how temperature and pH affect an enzyme.
• Identify an optimum and explain denaturation.

Theory

Amylase is an enzyme that breaks starch down to maltose. Iodine turns blue-black with starch, so the time taken until a sample no longer turns blue-black shows how fast the enzyme is working: rate ∝ 1 ÷ time. Warming speeds up the molecules, so the reaction gets faster up to the optimum temperature. Above it the enzyme’s shape changes (it is denatured), the substrate no longer fits the active site, and the rate falls sharply. Each enzyme also has an optimum pH.

starch → maltose (amylase)

Procedure

1. At pH 7, time the reaction at one temperature.
2. Repeat at six or more different temperatures, still at pH 7.
3. Go back to the fastest temperature and test an acidic buffer.
4. Plot rate against temperature for pH 7.

Precautions

• Let the enzyme and starch reach the bath temperature before mixing.
• Use a fresh well of iodine for each sample.
• A reading of 600 s means the starch was still there when you stopped.

Subject

Biology

Grade

9–12

Chapter

Life Processes (Nepal National Curriculum (CDC), grade 10)

Difficulty

Medium

Duration

30 min

Safety level

Low

Version

1.0

Apparatus

• Amylase solution
• Starch suspension
• Buffer solutions
• Iodine solution
• Spotting tile
• Water baths
• Thermometer
• Stopwatch