Understanding the enzyme CATALASE – Lab #
ESL level - 150 PTS
Observing the enzyme CATALASE – read & underline or highlight (10 pts)
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.
PRELAB REVIEW:
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.
Objectives:
1. identify tissues that have the enzyme catalase
2. study the enzyme catalase activity
3. explore factors that affect enzyme action (pH, Temperature, etc.)
4. understand that enzymes are specific and reusable
Pre-Lab Questions (20 pts)
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: _____________________________________________________
DATA
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2 points/question
10 points/chart with
description & color
Part I - Normal Catalase Activity
Occurrence of Catalase
1. Catalase is present in many kinds of living tissues. You will test for the presence of catalase in
tissues other than liver.
2. 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? ____________________________________________.
TABLE 1: Occurrence of Catalase
2 mL H2O2 +
2 mL H2O2 +
Liver catalase
Chicken catalase
Description:
Rate of reaction __
2 mL H2O2 +
Apple catalase
2 mL H2O2 +
Potato catalase
Description:
Description:
Description:
Rate of reaction __
Rate of reaction __
Rate of reaction __
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 to5= very fast).
Is Catalase Reusable?
3. Place 2 ml of the 3% hydrogen peroxide solution into a clean test tube
4. Add a small piece of liver to one test tube. Observe the bubbles; what gas is being released?
_________
5. 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.
6. Has it gotten warmer or colder? Is the reaction endothermic or exothermic? __________________
Is Catalase Reusable? ________________________
7. 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? ________________________________
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? _______________.
TABLE 2: Is Catalase Reusable?
2 mL H2O2 + liver Description:
Reaction rate __
Liquid + new liver
Reaction rate __ Why?
Description:
Description:
New H2O2 + old liver
Reaction rate __ Why?
Description:
Part II – Effect of Temperature on Catalase Activity
PROCEDURE
9. Put a piece of boiled liver into the bottom of a clean test tube and cover it with a small amount of
distilled water. What will boiling do to an enzyme? ___________________________________.
10. Add 2 ml of hydrogen peroxide to the boiled liver. What is happening in the test tube?
_____________ _______________________ Record the reaction rate (0-5) in DATA TABLE 2.
11. 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)
12. 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? _______________________
Table 3: Effect of Temperature on Catalase
2 mL H2O2 + boiled Liver
2 mL H2O2 + liver catalase
o
catalase (___ C)
In warm water bath (__ oC)
Rate of reaction __
Description:
Rate of reaction __
Description:
2 mL H2O2 + liver catalase
In iced water bath (__ oC)
Rate of reaction __
Description:
Part III – Effect of pH on Catalase Activity
PROCEDURE
12. 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 4.
13. Next, add a small piece of liver to each test tube. Estimate the reaction rates (0-5) and record in
DATA TABLE 4.
14. Does there appear to be a pH "optimum"? __________ At what pH? _____________
What is the effect of low or high pH on enzyme activity? __________________________.
Table 4: Effect of pH on Catalase Activity
3 mL H2O2 + boiled Liver catalase 3 mL H2O2 + liver catalase
At pH 3 (HCl)
At pH 7 (H2O)
Rate of reaction __
Rate of reaction __
Description:
Description:
3 mL H2O2 + liver catalase
At pH 10 (NaOH)
Rate of reaction __
Description:
Write one page (2-3 paragraphs) summarizing what you learned about enzymes. What
are they? Their structure? What do they do? What affects the way they work?
Anything special? 20 pts