Enzyme Rate of Reaction Trypsin

Overview

The video demonstrates an A-level biology practical investigating how temperature affects the rate of an enzyme-controlled reaction.

The enzyme, trypsin, is a protease that breaks down the milk protein casein into smaller, soluble peptides. As the reaction proceeds, the milk becomes clearer, allowing a marked cross behind the test tube to become visible.

Method

1. Prepare a water bath at about 40°C. Use a thermostatically controlled bath, or mix warm and cold water to reach the target temperature.
2. Set up two test tubes and mark a cross on one side of each:
   • Label one tube T for trypsin.
   • Label the other C for the control.
3. Add 10 cm³ of 3% powdered milk solution to each tube. Powdered milk works well for this experiment.
4. Add the following to each tube:
   • Control (C): 4 cm³ of pH 7 buffer.
   • Trypsin (T): 2 cm³ of pH 7 buffer.
5. Place the tubes in the water bath for about 5 minutes so the solutions reach the chosen temperature. Keep 2 cm³ of 0.5% trypsin solution at the same temperature.
6. Add the trypsin solution to tube T, mix gently, and return the tube to the water bath. Mix the control tube in the same way, but without adding trypsin.
7. Start the timer as soon as the enzyme is mixed with the milk. Watch for the cross behind the trypsin tube to become visible, then stop the timer and record the time. In the control tube, the milk should remain cloudy and the cross should not become visible.
   • Alternatively, place the tube in front of a printed cross or text and time how long it takes for the mark or text to become visible.
8. Repeat the experiment at several temperatures. The example uses 20, 30, 40, 50, 60 and 70°C.

Results and interpretation

Calculate the reaction rate as 1 ÷ the time taken, with time measured in seconds. The rate can be expressed in s⁻¹; values may be conveniently presented in standard form.

Plot reaction rate against temperature, with temperature on the x-axis. In the example results, the highest rate appears to be around 40°C.

As temperature increases towards the apparent optimum, molecular movement and enzyme–substrate collisions initially increase, raising the reaction rate. Above the optimum, the rate falls because sufficiently high temperatures can denature the enzyme and alter its active site.

The exact optimum cannot be established confidently from the example alone. Measurements taken at 10°C intervals may miss the true peak, so testing additional temperatures near 40°C would give a more precise estimate.

Speaker

The video features one presenter/narrator, who demonstrates and explains the practical. No other speakers or sources are identified.