Enzyme Catalase

Author(s): Afrodita Fuentes
Instrumentation - Teacher's Guide
SED 695B

Overview: 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.

Catalase - enzyme lab materials

  • Liver - $1.50/pound at a any grocery store: enough for 40 groups (5 classes)
  • 3% Hydrogen peroxide - 1 gallon ~$5.00 at Smart & Final: enough fro 5 groups
  • Ice
  • NaOH
  • HCl
  • pH paper
  • glassware
 

Topics:

  • enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium.
  • enzyme activity depend on the temperature, ionic conditions, and pH of the surroundings.

Experiment Summary

Before you begin this lab, review pH. Recall that pH is the measure of the acidity or alkalinity of a solution. An acidic solution has many hydrogen ions (H+) and a pH below 7. An alkaline, or basic, solution has very few hydrogen ions and a pH above 7. A neutral solution has a pH of 7.
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.

This lab sonsists of four activities:

  1. Observing normal catalase activity - catalase in reusable
  2. Identifying tissues that contain catalase
  3. Measuring the Effect of Temperature on Catalase Activity
  4. Measuring the Effect of pH of Catalase Activity

Standards: Biology/Life Sciences - Cell Biology

b. Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings.

 

Procedure: Understand the enzyme Catalase

word files: for ESL students | for general biology

Pre-Lab Questions

1. The reaction is _______________________________________

2. Why is this reaction necessary in the body?


3. The enzyme is ________________ & the substrate is ___________________ (H2O2).

4. The reactants are _______________________ & the products are ________________

5. Protein Denaturation is ____________________________________________.

6. Denaturation is caused by ________________________________________________.

7. Independent variables: ___________________________________________________

8. Dependent variables: _____________________________________________________

Part I – PROCEDURE -- Normal Catalase Activity

  1. Place 2 ml of the 3% hydrogen peroxide solution into a clean test tube
  2. Add a small piece of liver to one test tube. Observe the bubbles; what gas is being released?
  3. 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.
  4. 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.
  5. Has it gotten warmer or colder? Is the reaction endothermic or exothermic? Is Catalase Reusable?
  6. Pour off the liquid into a second clean test tube. Assuming the reaction is complete. What is this liquid composed of? What do you think would happen if you added more liver to this liquid? Why?
  7. Add another 2 ml of hydrogen peroxide to the liver remaining in the first test tube.
    Can you observe a reaction? What do you think would happen if you poured off this liquid and added more hydrogen peroxide to the remaining liver? Are enzymes reusable?

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.

  1. 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. Which tissues contained catalase?

Part II – PROCEDURE -- Effect of Temperature on Catalase Activity

  1. 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. What will boiling do to an enzyme?
  2. 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.
  3. 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)
  4. After 3 minutes, pour each tube of H2O2 into the corresponding 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.
    What is the "optimum" temperature for catalase? (This is the temperature at which the reaction proceeds fastest.)
    Why did the reaction proceed slowly at 0 deg.C?
    Why did the reaction not proceed at all at 100 deg.C?

Part III – PROCEDURE -- Effect of pH on Catalase Activity

  1. Add 2 ml hydrogen peroxide to each of 3 clean test tubes. Treat each tube as follows:
    Tube 1--add a drop of 1molar HCl (acid) at a time until pH 3.
    Tube 2--add a drop of 1molar NaOH (base) at a time until pH 10.
    Tube 3--adjust the pH to 7 by adding single drops of either 1molar HCl or 1molar NaOH as needed.
    CAUTION: Do not let acids or bases contact your skin or clothing. Swirl each test tube after adding each drop and measure the pH of each solution with pH paper. To do this, remove a drop or two of solution from a test tube using a clean glass stirring rod. Rinse your stirring rod and wipe dry before you dip it into each test tube. Place the drop on pH paper. Record the pH of each solution in DATA TABLE 3.
  2. Next, add a small piece of liver to each test tube. Estimate the reaction rates (0-5) and record in DATA TABLE 3.
  3. Does there appear to be a pH "optimum"? At what pH?
    What is the effect of low or high pH on enzyme activity?

Questions:

  1. What tissues contain the most enzyme catalase?
  2. Explain how the catalase is a reusable enzyme.
  3. What will boiling do to an enzyme?
  4. What is the "optimum" temperature for catalase?
  5. Why did the reaction proceed slowly at 0 deg.C?
  6. Why did the reaction not proceed at all at 100 deg.C?
  7. Does there appear to be a pH "optimum"? At what pH?
  8. What is the effect of low or high pH on enzyme activity?

Applications to everyday life:

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.

Occurrence of Catalase photos

Descriptions

  • liver seems to have the most catalase because there are more bubbles
  • apples do not have catalase

Questions (see above)

Observe the bubbles; what gas is being released?

Has it gotten warmer or colder? _________Is the reaction endothermic or exothermic? ____________


8. Add another 2 ml of hydrogen peroxide to the liver remaining in the first test tube. Can you observe a reaction? ____________ What do you think would happen if you poured off this liquid and added more hydrogen peroxide to the remaining liver? ______________________________
Are enzymes reusable? _______________.

Catalase is reusable photos

Description

Old liver keeps working because the enzyme catalase is in it. (have added hydrogen peroxide about 15 times and it still works. With this activity, students really get that enzymes are reusable)

Questions

  • Is Catalase Reusable? ________________________
  • Pour off the liquid into a second clean test tube. Assuming the reaction is complete. What is this liquid composed of? ___________________ What do you think would happen if you added more liver to this liquid? ________________________Why? ________________________________

 

Effect of Temperature on Catalase photos

Description / questions

  • What will boiling do to an enzyme?
  • What is the "optimum" temperature for catalase?
  • Why did the reaction proceed slowly at 0 deg.C? _______________________

Effect of pH on Catalase photos

Description / questions

  • Does there appear to be a pH "optimum"? __________ At what pH? _____________
  • What is the effect of low or high pH on enzyme activity? __________________________.
   

References & Links:

A website found about 3 years ago.