1. How are enzyme activities affected by temperature and pH ?
 Enzyme activity is usually expressed in terms of reaction rate.
the rate at which substrates are used up or broken down, or the rate of formation of product(s)
increase to a maximum and then decrease as the temperature increases

2.  Enzymes may be inactive and the reaction rate is low.
At low temperatures:
 Enzymes may be inactive and the reaction rate is low.
As the temperature rises:
 Substrate and enzyme molecules have more kinetic energy and vibrate more rapidly.
enzyme
activity
temperature

3. This enzyme works best at 40 ℃ !
 The chance of hitting each other to form an enzyme-substrate complex increases, thus have a higher reaction rate.
 The reaction rate is the highest at the optimum temperature.
enzyme
activity
temperature
40 ℃
This enzyme works best at 40 ℃ !

4.  When the temperature is above the optimum,
shapes of enzyme molecules begin to change.
 Denaturation of enzyme
enzyme
activity
 Enzyme loses its function and enzyme activity drops!
temperature
40 ℃

5. 2 pH  Because change in pH value also changes the shape of an enzyme.
 Enzymes usually work within a narrow range of pH.
Enzyme activity pH
 Because change in pH value also changes the shape of an enzyme.

6.  A great change in pH can cause denaturation.
 Enzymes work best at their optimum pH .
pepsin
salivary
amylase
Optimum pH for pepsin is __. 2
Optimum pH for salivary amylase is __.
Enzyme activity 7
pancreatic
lipase
Optimum pH for pancreatic lipase is ___. 10 pH
 A great change in pH can cause denaturation.

7. Applications of enzymes
 Protease are added to some washing powders to help in cleaning.
An enzyme to digest proteins.
Why proteases are added ??

8. Applications of enzymes
 Papain from plants like papayas are added to meat tenderizers to soften meat.
What is
papain??
It is an enzyme!! (Remember that?)

9. Applications of enzymes
 Some contact lens cleaners contain proteases to remove proteins.

10. Applications of enzymes
 Cellulase is used to produce stonewashed jeans.
What is cellulase?
Is it an enzyme?
Cellulase is an enzyme to digest cellulose!

11. Design a fair test to compare the enzyme activities of two biological washing powders.
Discuss with your group members and present your ideas on the following items:
The method used to solve the problem. (Use labelled diagrams to illustrate the procedures!).
The way by which experimental results is collected.
The independent, dependent and controlled variables of this investigation.

12. Investigation of protease activities in different fruit juices
Procedures:
1 Heat the end of a cork borer in a Bunsen flame and allow it to cool.
2 Gently press the borer down into the milk-agar to make 5 wells. Replace the lid quickly.
3 Make a mark on the plate to indicate the arrangement of samples.

13. different fruit juices
Investigation of protease activities in different fruit juices
4 Use a clean dropper to fill up each wells with pineapple juice, Kiwi fruit juice, papaya juice, pineapple juice and distilled water.
different fruit juices
distilled water
5 Replace the lid. Incubate the plate at 35 ℃ for one hour.
Home
Back
Next

14. Investigation of protease activities in different fruit juices
6 Measure the diameter of the clear zones around the wells by placing the plate on a graph paper and examining against light.
Home
Back
Next