Liver Enzyme Lab
Purpose: In this lab, you will hypothesize about how environmental factors affect the
activity of an enzyme. You will focus on how enzymes function and what affects their
reaction rate and ability to work.
Introduction:
In our cells there are many reactions occurring. One by-product from these reactions is
hydrogen peroxide. Hydrogen peroxide can be toxic to our bodies if a sufficient amount
is built up, so our cells contain an enzyme, peroxidase, which helps break down
hydrogen peroxide into non-harmful substances. The reaction that takes place is shown
below:
2H2O2 (Hydrogen Peroxide) 2H2O (water) + O2 (Oxygen)
2 hydrogen peroxide molecules react to form 2 water molecules and 1 oxygen molecule.
This reaction is VERY SLOW without an enzyme.
Since enzymes remain unchanged in a reaction, peroxidase is able to catalyze a new
reaction over and over until all of the hydrogen peroxide is broken down.
The cells we are extracting the enzymes from are chicken liver cells because they contain
large amounts of peroxidase, since the function of the liver is to detoxify and purify
substances in our bodies.
PreLab:
Before the lab do the following in your lab book. The final lab report will need it typed.
1. Title (should be pertinent to the lab), name, and period
2. Purpose (rephrase in your own words)
3. Pre-lab questions (answer in full sentences when appropriate)
a) Define an enzyme
b) What 3 factors might affect the reaction rate of peroxidase?
Knowing that the peroxidase reaction usually occurs in the liver and
not in a test tube, which 2 of these factors are not likely to affect the
reaction rate and why? Think about the fact that certain things are
tightly controlled by our bodies.
c) The peroxidase reaction is a decomposition reaction. Using a diagram,
show how the lock-and-key model can show the peroxidase
reaction with 2 molecules of hydrogen peroxide. Make sure you
show the true products that are formed at the end. Use page 52 as
an example of a model that breaks apart a different substrate. You
must change the names of substrates, products and the enzyme.
4. Hypothesis predictions: Fill in the data table with predictions
Procedure for Experiment:
Work in groups of 4
Materials list:
8 empty test tubes
1 glass graduated cylinder
1 plastic graduated cylinder
2 timers
40 ml enzyme slurry in a beaker
Test tube rack
Shared equipment:
Room temperature racks
37oC. water bath (body temperature)
60oC. water bath
Ice water bath
Test tube brushes
PROCEDURE
1. Gather equipment
2. Make sure you record the temperatures of the water baths in your data table.
3. In 4 empty test tubes, using the plastic graduated cylinder, measure out and place
5 ml of the enzyme solution
4. In 4 empty test tubes, using the glass graduated cylinder, measure out and place
10 ml of the 1.5% peroxide solution.
5. Mark 1 enzyme solution tube and 1 peroxide tube with temp. and your initials
 “ice water” (cold temp)
 “60+oC” (hot temp)
 “37oC” (body temp)
 “Room temp”
Place them in the correct water baths for at least 5 minutes
6. Gather your room temperature and ice water test tubes first.
7. Do not bring out the 37 and 60+ tubes yet.
8. Starting with your ice water test tubes, add the hydrogen peroxide to the enzyme
solution (clear to the pink) and start the stop watch. As the two solutions are
reacting, slowly move the test tube at a constant rate to help mix them.
9. Now add the room temp hydrogen peroxide to the pink enzyme solution. Start
your second timer. A second person should be timing this reaction.
10. Hint: in a group of 4, one person should be mixing and looking for bubbles in the
room temp. tube, while a second person should be timing. When the bubbles
have stopped forming, stop the timer. Bubbles may cling to the tube. This does
not mean they are still forming. Look carefully for formation of new bubbles.
The third person should be mixing the ice water tube, while the fourth person is
timing the ice water tube.
11. Once a reaction is complete, set the tubes aside and go retrieve the “37oC.” tubes
or the “60+oC” tubes.
12. Repeat steps 8-10 with both the “37oC.” tubes and the “60+oC” tubes.
13. Dispose of the solutions by rinsing them down the sink
14. When you have disposed of everything, clean up by using a test tube brush to
clean out the test tubes and place everything back to where it belongs.
15. The last few set ups (enzymes in acid at pH=3 and highly concentrated enzyme)
will be demonstrated by the teacher at a later time.
Data:
Changes to the
Enzyme
Solution
(manipulated
variable)
Peroxidase at
cold
temperature
_____oC.
Peroxidase at
room
temperature
_____oC.
Peroxidase at
body
temperature
_____oC.
Peroxidase at
warmest
temperature
_____oC.
Peroxidase at a
high
concentration
(demo)
Peroxidase at
low ph (=3)
(demo)
Predictions:
Will it be
greater or less
than the
reaction at
room
temperature and
neutral pH?
Time it take for
the reaction to
finish in
seconds
(responding
variable)
Ranking from
lowest – 1 to
highest rate - 6
of reaction
Final Lab Report: Due _______________
Order:
1. Pre-lab
2. Procedure you were provided
3. Data table neatly filled out.
4. Line graph of Reaction time vs. temperature (real graph paper or Excel).
Graph needs a title and X and Y axis clearly marked .
5. Analysis questions
Analysis questions. Typed and in full sentences.
1. Were there any results that surprised you?
2. With the various temperatures (cold, room temp, body temp, hot), which one had
the greatest activity? Propose a reason why this would be.
3. For two situations where there was no reaction (or very little), propose reasons for
these results. Think about how an enzyme’s shape plays a role in its ability to
function.
4. What can you conclude from your graph about the relationship between
temperature and reaction rate? Remember that reaction time and reaction rate are
not the same thing (slower rate means longer reaction time).
5. What can you conclude from your graph about what happens to the reaction and
to peroxidase when the temperature is too high?
6. The body’s internal pH is highly regulated to be between 7.3 and 7.4. This is true
for liver cells as well. If you had a pH regulation problem, which can occur in
some bacterial infections, and the pH of your liver cells dropped, hypothesize
what might happen to your ability to catalyze hydrogen peroxide.