HOW ENZYMES WORK
BACKGROUND:
Food supplies us with energy but before we can use the food we eat it must be broken down
into smaller units (monomers) to be absorbed into our blood and carried to our cells to produce energy.
The breakdown f food I called digestion. Elsewhere in our bodies poisons are produced by using the
food to make energy and these poisons can build up and cause the death of cells, tissues, or organs
which can lead to the death of the organism (us). To breakdown food and to breakdown or change
poisons we use enzymes.
Enzymes are protein catalysts. Catalysts speed up chemical reactions by helping reactants get
together and by reducing activation energy. In the lab scientists use heat to start reactions. We can’t
use heat in our bodies because we might initiate many more reactions than we need to have happen o
we might cause reactions to happen too quickly and destroy ourselves. Enzymes reduce the need for
heat by reducing the activation energy. Enzymes also are specific for the reactions they regulate to
ensure that only the reactions needed take place at any given time. Some enzymes act inside of cells
(intracellular enzymes), others move out of the cell to do their work (extracellular enzymes).
There are several types of chemicals reactions occurring in this lab: dehydration and hydrolysis
reactions and endothermic and exothermic reactions. In dehydration synthesis reactions molecules are
joined together by removing water. In hydrolysis reactions compounds are broken apart by adding
water. In endothermic reactions, heat is absorbed and bonds are formed. In exothermic reactions heat
is released and bonds are broken.
In this lab you will first model enzyme activity to better understand how enzymes work, and
then you will study how an enzyme functions in living tissue. The enzyme you will study in living tissue is
catalase. Catalase acts within a cell to breakdown hydrogen peroxide, a toxic metabolic waste of cell
activity, into the two harmless substances water and oxygen preventing cell death.
REACTION: 2H2O2  2H2O + O2
Enzymes and substrates join at a point called the active site. Hydrogen peroxide is the substrate
for the enzyme catalase. Competitive inhibitors are shaped like the enzyme but will not cause a reaction
in the substrate.
In this lab you will us liver, muscle tissue, apple, carrot, and potato. Even though these tissues
are no longer living, the enzymes remain active as long as the tissues are kept refrigerated.
OBJECTIVES:
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To understand the action of enzymes by using molecular models.
To experimentally test for the presence of catalase in living tissue.
To demonstrate the activity of an enzyme in living tissues.
To discover how changes in temperature affect enzyme activity.
To examine the effect of a competitive inhibitor on enzyme activity.
To construct a model of competitive inhibition.
SAFETY PRECAUTIONS:
MATERIALS:
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10 test tubes
Stirring rods
Fresh apple
Fresh potato
Fresh liver
Fresh carrot
Fresh chicken meat
10 mL graduated cylinders
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37o C water bath
22o C water bath
0o C water bath
100o C water bath
5 % hydroxylamine solution
3 % hydrogen peroxide solution
Scissors
Paper
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Test tube rack
Scalpel
Thermometer
Forceps
Graph paper
Distilled water
PROCEDURE:
Part 1: How Enzymes Work In Living Cells
1. Use only clean glassware. If necessary, clean all test tubes before use. Label two
clean test tubes A and B.
2. Pour two milliliters of 3% hydrogen peroxide into clean test tube A.
3. Using forceps and the scalpel cut a pea size piece of liver from the liver sample and
drop it into test tube A. Use the glass rod to push the liver into the hydrogen
peroxide if necessary. Observe and record your observations.
4. Feel test tube A and record which type of reaction is occurring.
5. Pour off the liquid from test tube A into clean test tube B. Add a new piece of liver
into test tube B and record the results.
6. Add two milliliters of new 3% hydrogen peroxide to the liver in test tube A and
record the results.
7. Explain the results in test tubes A and B and determine if enzymes are reusable.
Part 2: What Types Of Tissue Have Catalase?
1. Construct a table listing liver, chicken muscle, carrot, potato, and apple. Add a
second column to record the presence of catalase. You are going to rate your
catalase reactions on a scale of 1 to 5 with 5 being the most reactive (based on the
amount of bubbles produced by the food).
2. Label six clean test tubes A, B, C, D, E, and F.
3. Add two milliliters of hydrogen peroxide to each of the six test tubes.
4. To test tube A, add a piece of liver. Record your results in your table
5. To test tube B, add a piece of chicken muscle (all pieces must be the same size).
Record your results in your table.
6. To test tube C, add a piece of carrot. Record your results in your table.
7. To test tube D, add a piece of potato. Record your results in your table.
8. To test tube E, add a piece of apple. Record your results in your table.
9. To test tube F, add 1 mL of water. Record your results in your table. What is the
role of this test tube?
10. Create a graph of your data.
Part 3: How Does Temperature Affect Enzyme Activity?
1. Label four clean test tubes A, B, C, and D.
2. Add a pea size piece of liver into each test tube.
3. Add water to test tube A (just enough to cover the liver) and place it in a boiling
water bath for 5 minutes.
4. Label 3 test tubes B1, C1, D1. Pour two milliliters of hydrogen peroxide into each of
these test tubes.
5. Place test tubes B and B1 into a beaker of ice for five minutes.
6. Place test tubes C and C1 into a beaker of 22OC water for five minutes.
7. Place test tubes D and D1 into a beaker of 37oC water for five minutes.
8. After the five minutes of treatment, pour two milliliters of 3% hydrogen peroxide
into test tube a and record the results on a scale of 1-5 with 5 being the most
reactive (most bubbles).
9. Now pour test tube B1 into test tube B and record the results.
10. Now pour test tube C1 into test tube C and record the results.
11. Now pour test tube D1 into test tube D and record the results.
12. Record the results in a table listing temperature and reaction rate. Then create a
graph based on that data.
ANALYSIS:
1. How do enzymes work to aid chemical reactions?
2. Examine your table from part 2. Which type of tissue has the most catalase present? Look up
what that tissue does for the organism it is in and explain why it might have the most catalase.
3. Examine the temperature table. What do you think is the ideal temperature for the operation
of catalase enzyme? Explain.
4. Examine the temperature table. Denature means to change shape. When an enzyme
denatures, it changes shape and will no longer affect the substrate. What temperature or
temperatures probably denature(s) catalase?
5. Does cold denature catalase or just slow it down? Explain.
6. What do you think happens to the heat released by the decomposition of hydrogen peroxide in
living cells?
7. Are enzymes reusable? Use the results for test tubes A and B in Part II to explain your answer.
Lab Report Format - Individual
Your lab report is to be typed, double-spaced, and in 12-font. The report is to include the following
sections:
1. Testable question
a. What are you investigating in the lab activity? You need a testable question for each
part of the lab
2. Hypothesis
a. one for each part of the lab
3. Data
a. Parts 1, 2, 3, 4. Include drawings, tables, graphs, and observations
4. Conclusions
5. Analysis #1-7
a. Type question and answer