Name: _______________________
Enzyme Catalysis Lab/Testing Catalast Activity using Vernier Lab Quest
Introduction
Hydrogen peroxide (H2O2) is produced naturally inside many of your cells. The
trouble is, it is very toxic to us. To deal with this, we produce an enzyme called catalase
that breaks down hydrogen peroxide into harmless substances.
2H2O2  2H20 + 02
The equation above illustrates an example of catalysis, which means something is getting
broken down. A catabolic enzyme helps to break something down. If an enzyme helps to
build a molecule, rather than breaking it down, it is called an anabolic enzyme.
Let’s review some things about enzymes. Enzymes are globular proteins that are
responsible for most of the chemical activities of living organisms. Enzymes act as
catalysts; substances that speed up chemical reactions without being destroyed or
changed during the process. Enzymes are very efficient, and can be used over and over
again. One enzyme may very well catalyze hundreds, or even thousands of reactions
every second! With all these impressive things about enzymes, they come with some
conditions attached. Most enzymes are very picky about the situations in which they will
work. Temperature is a very important factor, as is pH. If the environment is too hot or
too cold, or too acidic or too basic, the enzyme may not catalyze its reaction at all. In fact,
if the conditions get too extreme the enzyme may quit working altogether because its
structure may become distorted. In these cases, we say that the enzyme has become
denatured.
In this experiment, you will measure the rate of enzyme (catalase) activity under
various conditions. You will measure the pressure of oxygen gas in a flask as it is
produced from the breakdown of hydrogen peroxide by catalase.
Objectives
 Measure and compare the initial rates of reaction for this enzyme when different
concentrations of enzyme react with H2O2.
 Measure and compare the initial rates of reaction for the enzyme at various
temperatures.
 Measure the production of oxygen gas in a flask as it is produced from the
breakdown of hydrogen peroxide by catalase.
Procedure:
1. Pay close attention to the set up of the apparatus. Your teacher will demonstrate
for you the set-up of the experiment.
2. With the Cable and the LabQuest linked, and with the Gas Pressure Sensor
plugged into channel 1 of the LabQuest. Make sure that the LabQuest is turned on.
Name: _______________________
3. The LabQuest should automatically begin reading the pressure. Make sure that
the reading is in mmHg, not kPA. (To change, use the stylus to click on the unit.
A menu will pop out; click on change units. Change to mmHg.)
4. Along the right hand side of the data display screen, adjust the rate to be “1.0
samples/s,” and the length to be “30.0s”. This will get you a reading every second
for 30 seconds.
5. Add 5 mL of 3% hydrogen peroxide to the flask (this is the concentration of the
peroxide straight out of the bottle).
6. Draw 1mL of catalase into the syringe and be very careful NOT to allow any of
the enzyme into the flask yet. ** Make sure the air valve on the pressure sensor
tube is open or closed as needed! **
Here is where teamwork is critical!
7. The next steps should be done quickly!! Start the data collection by pressing the
“Play” button on your vernier. IMMEDIATELY squirt the catalase from the
syringe into the flask containing the peroxide. IMMEDIATELY put the stopper on
the flask. START, SQUIRT, STOPPER! HOLD THE STOPPER ON THE
FLASK, but be careful NOT to disturb the flask while the experiment is running
(don’t bump it, shake it, knock it over).
8. The collection will automatically stop after 30 seconds. Once it stops, the
LabQuest will display a graph of your experiment.
9. Determine the rate of enzyme activity for the curve of pressure vs. time.
a. Examine the graph and determine the most linear region (steepest part of the
graph)
b. Click your stylus on the first point of this region.
c. Enter the initial pressure and the initial time into the data table.
d. Move the cursor to the last point of the region you selected.
e. Determine the slope for the segment of the graph you chose by using the
following formula:
Pf - Pi
tf - ti
10. Let’s check your math! Use your stylus to click where the data values begin to
increase. Hold it down on the screen and drag to the point where the pressure
values no longer increase and pick up your stylus off of the screen.
11. Next, click on the analyze menu. Click on curve fit, check the box “pressure.” This
will bring you to a menu with the graph on the left hand side. Click the down
arrow next to Fit Equation, and choose “Linear.” The data for the best fit line will
appear on the screen. Compare the “m” value on the screen (the slope of the line—
rate of change) with the slope that you calculated in #9.
You are now ready to do another trial. Make sure to thoroughly rinse out your flask in
between each trial.
Name: _______________________
12. Repeat the procedure using 0.5 mL of catalase. Then repeat using 2 mL of
catalase. Predict what will happen to the slope of the line in each of these trials:
13. Repeat the procedure using an ice-water bath. Predict what will happen? Explain
your prediction.
14. Repeat the procedure using a warm-water bath. Predict what will happen? Explain
your prediction.
15. Repeat the procedure by diluting the peroxide. Add 5mL of 3% peroxide to the
flask, then add 5mL of distilled water to the flask.
Question: What is the concentration of the peroxide in the flask now?
Predict what will happen? Explain your prediction.
16. Repeat the original procedure using 1mL of the boiled enzyme. Predict what will
happen? Why?
Name: _______________________
Conditions
P- initial
1 ml catalase
0.5 ml catalase
2 ml catalase
Dilute peroxide
Boiled catalase
P- final
t- initial
t- final
Slope (Pf-Pi/tf-ti)
Your choice
Analysis:
1. If you put hydrogen peroxide on a cut on your finger, you see bubbles coming from
the cut. Explain what is happening.
2. In the first part of this experiment when you varied the concentration of the catalase,
what is the independent variable? What is the dependent variable?
3. Many of your cells produce catalase, Since catalase is an enzyme, it is also a protein.
At the cellular level, describe the general process of how you make a catalase.
4. What is a catalyst?
5. What is meant when we say that an enzyme has become denatured?
6. Explain why a pressure sensor was used in this experiment.
7. Did the reaction rate for the enzyme activity stay the same throughout the entire
experiment? How can you tell? What is the significance of this?
Name: _______________________
8. If you increased the amount of enzyme to 10ml what do you think would happen to
the rate of reaction? Predict what the rate would be.
9. At what temperature is the rate of enzyme activity the highest? The lowest? Explain.
10. How does changing the temperature affect the rate of enzyme activity? Does this
follow a pattern you anticipated?
11. Why might the enzyme activity decrease at very high temperatures?