Name:____________________________ Class:_______________ Date:__________
Objectives
* Measure the effects of changes in temperature, pH, and enzyme concentration on reaction rates of an enzyme
catalyzed reaction in a controlled experiment.
* Explain how environmental factors affect the rate of enzyme-catalyzed reactions.
Enzyme Lab
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-uhLAYSS); it speeds up a reaction which breaks down hydrogen peroxide, a toxic chemical, into 2 harmless
substances--water and oxygen.
The reaction is: 2 H2O2 ----> 2 H2O + 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. In this lab, you will study the catalase found in liver cells. You will be using chicken or beef liver. It might
seem strange to use dead cells to study the function of enzymes. This is possible because when a cell dies, the
enzymes remain intact and active for several weeks, as long as the tissue is kept refrigerated.
MATERIALS:
1molar HCl solution
1molar NaOH solution
6 Test tubes
Measuring Pipette
10-ml Graduated cylinder
40 ml 3% Hydrogen peroxide
solution
(found in stores)
Straight-edged razor blade
Scissors and Forceps (tweezers)
pH paper (optional)
Stirring rod
Fresh liver, Apple, and
Potato
Test tube holders
Ice bath
Warm water bath
Boiling water bath
PART A - Observe Normal Catalase Reaction
1. Place 2 ml of the 3% hydrogen peroxide solution into a clean test tube.
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2. Using forceps and scissors cut a small piece of liver and add it to the test tube. Push it into the hydrogen
peroxide with a stirring rod. Observe the bubbles.
What gas is being released? (consider the equation) ______________________
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"
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?
____________________
3. Pour off the liquid into a second 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?
__________________________________
Test this and record the reaction rate. Reaction Rate ___________ (1 – 5)
4. Add another 2 ml of hydrogen peroxide to the liver remaining in the first test tube.
rate? ________
What is the reaction
Is catalase reusable? Explain how you know.
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
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Part B - What Tissues Contain Catalase
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 and then add each of the three test substances to the tubes. As you add each test
substance, record the reaction rate (0-5) for each tube.
Substance
Rate of Reaction (0-5)
Potato
Apple
Chicken
Based on your observations, which tissues contained
catalase? _________________________________________
Do some contain more catalase than others? How can you tell?
___________________________________________
PART C - What is the 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 water. Place this test tube in a boiling water bath for 5 minutes.
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 for hot test tubes.
What is the reaction rate for the boiled liver and peroxide? __________
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 an
ice bath. Place the other set in a warm water bath (not boiling).
After 3 minutes, pour each tube of H2O2 into the corresponding tube of
liver and observe the reaction
What is the reaction rate for the cold liver/peroxide? ______
What is the reaction rate for the warm liver/peroxide? ______
PART D - What is the Effect of pH on
Catalase Activity
1. Add 2 ml hydrogen peroxide to each of 5 clean test tubes.
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Tube 1--add 4 drops of hydrochloric acid, HCl (acid) pH =_______
Tube 3 – add 4 drops of sodium hydroxide, NaOH (base) pH =______
Tube 5 – add 3 drops of water (neutral) pH =_____
*(Optional) Using pH paper, determine the pH of your samples.
Now add liver to each of the test tubes (try to do it all at about the same time, so you can easily compare)
Rate of Reaction for: Acid _____ Neutral ______ Base_____
Part E - Design an Experiment
Lactaid is a product designed to help people who cannot digest milk sugar
(lactose) because they are missing the enzyme lactase. Many people are lactoseintolerant, a condition that is mainly genetic. Lactase breaks down lactose into
two subunits: glucose and galactose.
To test for the presence of monosaccharides and reducing disaccharide sugars in
food, the food sample is dissolved in water, and a small amount of Benedict's
reagent is added. The solution should progress in the colors of blue (with no
glucose present), green, yellow, orange, red, and then brick red or brown (with
high glucose present).
Design an experiment where you would determine how quickly lactaid works to
break down milk sugar. Be specific in your description, use drawings if
necessary.
DATA ANALYSIS
1. Describe the relationship between catalase and hydrogen peroxide. Indicate which is the enzyme, which is the
substrate and what occurs during the reaction. It may be helpful to write the equation. (2)
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
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2. Is catalase reusable? Use your data to support your answer. (1)
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
3. How does temperature and pH affect the reaction rate of catalase? Propose a way to refine your experiment
to find the exact, or OPTIMAL pH and temperature of catalase. (3)
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
4. In 2-3 sentences, summarize the data and information displayed in this graph.
______________________________
______________________________
______________________________
______________________________
______________________________
______________________________
______________________________
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Name: _______________________Class Period: _______Date: ______________________
Enzyme Lab Quiz
1. What is an enzyme?
a.
b.
c.
d.
carbohydrate
protein
lipid
nucleic acid
2. What enzyme were you testing in this lab?
a.
b.
c.
d.
e.
f.
hydrogen peroxide
liver
chicken
catalase
apple
potato
3. What was the gas being released when you added the
liver to the hydrogen peroxide?
a.
b.
c.
d.
e.
hydrogen
hydrogen peroxide
oxygen
water
catalase
4. The test tube should have felt warmer after the
reaction. That’s because this reaction was—
a. endothermic.
b. exothermic.
5. After the reaction, in part A, step 3, you poured the
remaining liquid into a second test tube. Then you
added some more liver to this liquid. Nothing should
have happened because this liquid is –
a.
b.
c.
d.
e.
water.
hydrogen peroxide.
blood.
oxygen.
hydrogen.
6. After the reaction, you were instructed to add more
hydrogen peroxide to the remaining liver. It should
have bubbled up significantly. What does this prove?
(part A, step 4)
a. This proves that there’s a lot of oxygen in
liver.
b. This proves that hydrogen peroxide is very
reactive.
c. This proves that the catalase is reusable.
d. This proves that it doesn’t matter what you put
with liver, it will always bubble.
7. After testing the potato, apple, and chicken you should
have observed that the chicken made the hydrogen
peroxide break down fastest. WHY?
a. The chicken was the only raw food.
b. The potato & apple oxidized so they didn’t
allow for the reaction to happen.
c. Although most foods contain catalase, meats
(chicken) generally have more protein and we
know that enzymes are proteins.
d. All foods contain equal amounts of catalase.
8. After cooking the liver in boiling water, the reaction
didn’t seem to work. But warming the liver slightly
seemed to make the reaction go faster. WHY?
a. If the enzyme gets too hot, it denatures
(breaks) & will no longer work.
b. Enzymes ONLY work at room temperature.
c. Enzymes make reactions go faster when
they’re exactly 32ºF.
9. Changing the pH of an enzyme can affect its
effectiveness. How could we refine our experiment to
determine the OPTIMAL pH?
a. We could have tested one solution with lemon
juice, one solution with bleach, and one
solution with vinegar.
b. We could have had several solutions ranging
from 1-14 and chosen the one that bubbled the
most.
c. We could have heated the acidic solutions.
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