Name________________________________ Block__________ Date___________________5.3- Enzyme Lab

Question: How do temperature and pH affect enzyme activity?

Background Information:What would happen to your cells if they made a poisonous chemical? You might think that they would die. In fact, your cells are always making poisonous chemicals. They do not die because your cells use enzymes to break down these poisonous chemicals into harmless substances. Enzymes are proteins that speed up the rate of reactions that would otherwise happen more slowly. The enzyme is not altered by the reaction. You have hundreds of different enzymes in each of your cells. A substrate is a substance on which an enzyme acts during a chemical reaction.

Each of these enzymes is responsible for one particular reaction that occurs in the cell. In this lab, you will study an enzyme that is found in the cells of many living tissues. The name of the enzyme is catalase (CAT-uh-LAYSS); it speeds up a reaction, which breaks down hydrogen peroxide, a toxic chemical, into 2 harmless substances--water and oxygen.

The reaction is as follows: H2O2 H2O + O2

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This reaction is important to cells because hydrogen peroxide (H2O2) is produced as a byproduct of many normal cellular reactions. If the cells did not break down the hydrogen peroxide, they would be poisoned and die. In this lab, you will study the enzyme catalase, found in potato cells. It might seem strange to use dead cells to study the function of enzymes. This is possible because when a cell dies, the enzymes remain intact and active for several weeks, as long as the tissue is kept refrigerated.

By using potatoes containing this enzyme, we can determine the effect of temperature and pH on enzyme activity.

I. In the reaction that you will be studying in this lab, what is the enzyme? What is the substrate? What are the products?

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II. Hypothesis 1: How do you think Temperature will affect enzyme activity? (If….then….)

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III. Hypothesis 2: How do you think pH will affect enzyme activity? (If….then….)

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Enzyme Substrate Products

Materials:

Potatoes Graduated cylinder

3 test tubes

Hydrogen peroxide

Ice bath

Hot pot

Acid solution

Base solution

Affect of Temperature on Enzyme Function Procedure:

1. Label 1 test tube “Ice Water”, 1 test tube “Room Temp”, and 1 test tube “Warm Water”

2. Add 5 ml of potato solution to each test tube. 

3. Place the first test tube in an ice bath for 5 minutes and record the temperature of the water in the table, below.

4. Leave the second test tube at room temperature for 5 minutes. Record the temperature in the table, below.

5. Place the third test tube in a warm water bath for 5 minutes. Record the temperature in the table, below.

6. Add 5mL of hydrogen peroxide to each test tube and record the relative amount of bubbling you see in each*.

*Estimate the rate of the reaction (how rapidly the solution bubbles) on a scale of 0-5 (0=no reaction, 1=slow, 5= very fast).

Clean out your test tubes by draining the liquid in the sink and throwing the potatoes in the trash.

Affect of pH on Enzyme Function Procedure: 

1. Label 1 test tube “Acid”, 1 test tube “Neutral”, and 1 test tube “Base”2. Add 5 mL of potato solution to each test tube.

3. Place 5 mL of acid solution in the first test tube.

4. Place 5 mL of water in a second test tube.

5. Place 5mL of base solution in the third test tube.

6. Add 5 ml of hydrogen peroxide to each tube and record the relative amount of bubbling you see in each*.

Clean out your test tubes by draining the liquid in the sink and throwing the potatoes in the trash.

5 mL potato

5 ml Acid+

5 ml potato+

5 ml H2O2

5ml H20+

5mL potato+

5 ml H2O2

5ml Base +

5 mL potato+

5 ml H2O2

Data and Observations:  

Temp (oC)

Rate of Enzyme Activity (0-5)

Ice Water

Room Temp

Warm Water

Boiling Water

pH Rate of Enzyme Activity (0-5)

Acid (3)

Neutral (7)

Base (10)

Graph your results, below.Graph 1: Affect of Temperature on enzyme activity

Conclusion Questions:  

IV. At what temperature was the enzyme activity the greatest? The least?

V. Did your “Affect of Temperature” results support your original hypothesis?

VI. At what pH was the enzyme activity the greatest? The least?

VII. Did your “Affect of pH” results support your original hypothesis?

VIII. What does the term denature mean? Why doesn’t a denatured protein function (your response should include the terms active site and substrate)?

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Graph 2: Affect of pH on enzyme activity