Name ____________________________________________________ Date _____________
Period ________
Biology: Ch 2 Biochemistry
Properties of Enzymes Lab
Purpose:
2.04 Investigate and describe the structure and function of enzymes and explain their importance in biological systems.
Materials:
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1 watch plate with MnO2 (for Observation section)
homogenate beef liver and potato, iced and boiled
chunks of beef liver and potato
3% H2O2 (Hydrogen peroxide)
distilled H2O
acetic acid (Vinegar)
carbonic acid (Diet coke)
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3 M NaOH and 3 M HCl (dropper bottles)
pH paper
A 24-well plate
Plastic 3 ml pipettes
stirring rod
10 ml graduated cylinder
clock with second hand or stop watches
Introduction:
Enzymes are proteins that speed up chemical reactions in living cells. They are biological catalysts. The enzyme you will
be studying is called catalase; it speeds up the breakdown of hydrogen peroxide which is a toxic waste product produced
by living systems in water and oxygen gas. In this lab, you will study the characteristics of enzymes and some of the
things that affect enzyme function. You may work with a partner; each student must complete their own lab sheet.
2H2O2
Observation:
2H2O
+
O2
How can you tell that catalase (the enzyme) is working?
Your teacher will demonstrate how MnO2 acts as a catalyzing agent to H2O2. Observe how Manganese Dioxide reacts to
Hydrogen peroxide. Describe what you see below. What type of gas do you think is being released?
Hypothesis: How do you think enzymes will react to the following situations? Explain your answer.
Activity 1: Is catalase specific to particular substrates?
Activity 2: Is the enzyme catalase reusable?
Activity 3: How does temperature affect enzyme function?
Activity 4: How would a change in pH affect enzyme function?
ACTIVITY 1: ARE ENZYMES SPECIFIC?
Example:
Procedure:
1. Locate the first row of your well plate, labeled A, B, C, and D.
2. Place about 1 ml of liver homogenate in each well.
3. Put 2 ml of the following substances in each tube as noted:
A: distilled water
B: hydrogen peroxide
C: acetic acid
D: carbonic acid
4. Observe the reactions and record results on a Table 1.
Table 1: Specificity of Enzymes
Well Letter
Description of Results with Liver Homogenate
(Reacted strongly, Reacted weakly, Did not react at all)
A: Distilled Water
B: Hydrogen Peroxide
C: Acetic Acid
D: Carbonic Acid
1.
Questions to Guide Analysis:
Are enzymes specific? What evidence do you have for your answer? (Which substance(s) appeared to react with the
liver homogenate?)
2. Which of the four organic compounds do enzymes belong to?
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ACTIVITY 2: ARE ENZYMES REUSABLE?
Procedure:
1. Locate the second row of your well plate E and F.
2. Put a pea-size piece of liver in each. Ready your stopwatch to time each reaction.
3. Add 2 ml H2O2 to well E; let the reaction come to completion. Record as reaction E on Table 2.
4. Using a pipette, transfer the liquid from well E onto the liver in well F. Record as reaction F on Table 2.
5. Then pour 2 ml of fresh H2O2 onto the old liver in well E. Record as reaction G on Table 2.
Table 2: Reusability of Enzymes
Reaction Letter (E, F, or G)
Time for Complete
Reaction (seconds)
E: Liver Piece + Peroxide
F: New Liver + Old Peroxide
G: Old Liver + New Peroxide
Comparative Description of Reactions
(Reacted strongly, Reacted weakly, Did not react at all)
Questions to Guide Analysis:
3. Which substance is reusable—the substrate or the enzyme? Support your answer with evidence.
4. In Reaction B, what is the “old peroxide?” (liquid)
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ACTIVITY 3: HOW DOES TEMPERATURE AFFECT ENZYME FUNCTION?
Procedure:
1. Locate the third row of your well plate H-M.
2. Add 2 ml of iced liver homogenate to well H and 2 ml iced potato homogenate to well K. Make sure you use the
homogenate supplies that are on ice.
3. Put 2 ml room temperature liver homogenate in well I and 2 ml room temperature potato homogenate into well L.
4. Put 2 ml boiled liver homogenate in well J and 2 ml boiled potato homogenate in well M.
5. Ready your stopwatch to time each reaction. Then, add 2 ml hydrogen peroxide to each well, H-M.
6. Observe reactions and record on Table 5.
Table 3: Temperature and Enzyme Action
Well Letter
Time for Complete
Reaction (seconds)
H: Liver on Ice
Comparative Description of Reactions
(Reacted strongly, Reacted weakly, Did not react at all)
I: Liver at Room
Temperature
J: Liver, Boiled
K: Potato on Ice
L: Potato, Room
Temperature
M: Potato, Boiled
Questions to Guide Analysis:
5. What is the relationship between temperature and enzyme activity? Use evidence from your experiments to support
your statement.
6. What happens to enzyme molecules in extreme temperatures?
7. What might happen to a human being if a fever gets too high?
ACTIVITY 4: HOW DO CHANGES IN pH AFFECT ENYZME FUNCTION?
Procedure:
1. Locate your fourth row N, O, and P.
2. Add 2 ml liver homogenate to each well.
3. Add 3M HCl and 3M NaOH as follows to the wells:
A: 1 drop 3M HCl
B: no acid/no base
C: 1 drop 3M NaOH
4. Measure the pH of each solution using pH paper. Be careful not to touch any of the liquid to your skin!
5. Ready your stopwatch to time each reaction. Add 1 ml of hydrogen peroxide to each well.
6. Observe reactions and record in Table 6.
Table 4: pH and Enzyme Activity
Well Letter
pH
Time for Complete
(0 to 14)
Reaction (seconds)
N: 1 drop HCl
Comparative Description of Reactions
(Reacted strongly, Reacted weakly, Did not react at all)
O: no acid/no base
P: 1 drop NaOH
Questions to Guide Analysis:
8. In Activity Four, which of the wells was your control? N, O, or P? How do you know?
9. What is the relationship between pH and enzyme activity? Refer to your results in your data table above.
10. Stomach enzymes work best at a pH of 2. How might a pH of 4 in the stomach affect digestion?
Conclusion to All Enzyme Activities:
Using all of the terms below, write a clear, well-supported paragraph describing everything you have learned about
enzymes in this lab investigation. Use these terms in your paragraph and underline them! Enzyme, Substrates,
Products, Temperature, pH, Denature, Catalase, Hydrogen Peroxide, Liver, Potato.)