BIOLOGY LAB
CATALASE
Observing an enzyme

INTRODUCTION:

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. 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 (KAT-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:

2H2O2 ----> 2H2O + O2

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 catalase found in liver cells. You will be using chicken or beef liver. 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.

PRELAB REVIEW:

Recall that the substrate is the molecule that the enzyme acts on, and the products are the molecules produced by the reaction. Review why enzymes are reusable.

Under certain conditions enzymes are denatured. An enzyme is denatured when the protein molecule loses its proper shape and cannot function. Some things that can denature an enzyme are high temperatures, extremes of pH, heavy metals, and alcohol.

MATERIALS:


6 Test tubes and rack Stirring rod
thermometer scissors and forceps

Fresh liver, chicken meat, Apple, and Potato Test Tube Holder

3 Beakers Graph Paper

10-ml Graduated cylinder
40 ml 3% Hydrogen peroxide solution

PROCEDURE:

Part I
Normal Catalase Activity
NOTE: Be sure to clean your stirring rod (and test tubes) between steps.

1. Place 2 ml of the 3% hydrogen peroxide solution into a clean test tube.

2. Using forceps and scissors, cut a small piece of liver and add it to the test tube. Push it into the hydrogen peroxide with a stirring rod.

Throughout this investigation you will 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). Assume that the reaction in step 2 proceeded at a rate of "4" and record the speed in DATA TABLE 1, and DATA TABLE 2 as the rate at room temperature.

3. Recall that a reaction that absorbs heat is endothermic; a reaction that gives off heat is exothermic. Now, feel the temperature of the test tube with your hand.

Has it gotten warmer or colder? Record this in your data section

Part 2

Is Catalase Reusable?

4. Place 2 ml of 3% hydrogen peroxide solution into a clean test tube and add a small piece of liver.

What is happening in your test tube?

5. Pour off the liquid into a second test tube.

6. Add another 2 ml of hydrogen peroxide to the liver remaining in the first test tube.

Record your observations in your data section

Part 3

Occurrence of Catalase

Catalase is present in many kinds of living tissues. You will now test for the presence of catalase in tissues other than liver.

7. Place 2 ml of hydrogen peroxide in each of 3 clean test tubes. To the first tube, add a small piece of potato. To the second tube, add a small piece of chicken. To the last tube, add a small piece of apple. As you add each test substance, record the reaction rate (0-5) for each tube in TABLE 1.

Part 4

Effect of Temperature on Catalase Activity

8. Put a piece of liver into the bottom of a clean test tube and cover it with a small amount of distilled water. Place this test tube in a boiling water bath for 5 minutes.

9. Remove the test tube from the hot water bath, allow it to air cool, then pour out the water. Add 2 ml of hydrogen peroxide. CAUTION: Use a test-tube holder when handling the hot test tubes.

What is happening in the test tube?

Record the reaction rate (0-5) in DATA TABLE 2.

10. Put equal quantities of liver into 2 clean test tubes and 1 ml H2O2 into 2 other test tubes. Put one test tube of liver and one of H2O2 into each of the following water baths: Ice bath (0 deg.C) and Warm water bath (37 deg.C)

11. After 3 minutes, pour each tube of H2O2 into the coresponding tube of liver and observe the reaction. Record the reaction rates (0-5) in DATA TABLE 2. You recorded the reaction rate for room temperature earlier. (You will be using this data to construct a graph)

Post-Lab Discussion Questions

1.  When you added the enzyme catalase to the hydrogen peroxide solution what gas was being released?

2.  Was the reaction endothermic or exothermic? Explain how you came to that conclusion.

3.  Assuming that the reaction had enough time to finish, what should the liquid be that remains in the test tube? Would there be a reaction if you added more catalase?

4.  Are enzymes reusable? What happened when you added more hydrogen peroxide to the used piece of liver?

5.  Using data table 1, which tissues contained the most catalase?

6.  What does boiling do to an enzyme?

7.  What was the optimum temperature for the catalase enzyme? Explain what happened at each temperature we tested.

8. What are some other things that can denature enzymes that we did not test in this experiment?

Name______Date______Period____

Enzyme Lab: Catalase

Pre-Lab Questions

1.  What is an enzyme?

2.  In this lab we will be testing the rate at which catalase can break down the poisonous chemical hydrogen peroxide in our bodies. What is the enzyme, and what is the substrate?

3.  Write the chemical equation for the breakdown of hydrogen peroxide.

4.  What do we call it when an enzyme looses its shape? What are 2 ways this could happen?

Results

Table 1: Table 2:

(You will use Table 2 to make a graph)

Observations

Part 1

Was the reaction hot or cold? Explain.

Part 2

What did you observe?