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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 - Place 2 ml of
the 3% hydrogen peroxide solution into a clean test tube
- Add a small piece of liver to one test tube. Observe
the bubbles; what gas is being released?
- 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.
- 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?
Is the reaction endothermic or exothermic?
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?
- 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.
- 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
- 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?
- 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.
- 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)
- 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
- 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.
- Next, add a small piece of liver to each test tube. Estimate
the reaction rates (0-5) and record in DATA TABLE 3.
- Does there
appear to be a pH "optimum"? At what pH?
What is the effect of low or high pH on enzyme activity?
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