Identifying Enzymes
Unit 2 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-uh-LAYSS); it speeds up a reaction which breaks down hydrogen peroxide, a toxic
chemical, into 2 harmless substances--water and oxygen. The reaction is as follows:
2H2O2 --------------------> 2H2O + 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 potato or liver cells.
Purpose/Problem
1. Measure the effects of changes in temperature, pH, and enzyme concentration on reaction rates of an enzyme-catalyzed
reaction in a controlled experiment.
2. Explain how environmental factors affect the rate of enzyme-catalyzed reactions.
Hypothesis:
Formulate two hypotheses based on Temp and pH of Enzymes. Be sure to use an “if, then, because” statement for both.
Materials
• 1molar HCl solution
• Stirring rod
(in dropper bottle)
• Potato or liver
• 1molar NaOH solution
• Scissors and Forceps (tweezers)
(in dropper bottle)
• 10-ml Graduated cylinder
• 6 Test tubes and Test tube holder
• Thermometer
• 40 ml 3% Hydrogen peroxide
solution (found in stores)
• pH paper
• (3) 250 ml Beakers
Procedures (Part A) – Observe Normal Catalase Reaction
1. Place 2 ml of the 3% hydrogen peroxide solution into a clean test tube.
2. Add a piece of potato to the test tube. Push it into the hydrogen peroxide with a stirring rod. Observe the bubbles.
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".
Procedure (Part B) – The Effect of Temperature on Catalase Activity
1. Obtain 6 test tubes. Fill 3 of the test tubes with 2 ml of hydrogen peroxide. Fill the other 3 test tubes with one piece of
potato.
2. Place 1 hydrogen peroxide tube & 1 potato tube in a hot water bath (100°C)
3. Place 1 hydrogen peroxide tube & 1 potato tube in an ice bath (0°C)
4. Place the remaining 2 test tube in a test tube rack at room temperature.
5. WAIT 3 MINUTES!!!!
6. Pour each tube of hydrogen peroxide tube into the corresponding temperature potato tube.
7. Draw the data table below into your Data/Observation section. Record the rate of the reaction (0-5) in the data table
below. Reminder: 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).
Temperature
Ice Bath
(0°C)
Room Temp
(24°C-37°C)
Hot Bath
(100°C)
Rate of
reaction (0-5)
Procedure (Part C) – The Effect of pH on Catalase Activity?
1. Obtain 1 acidic test tube (pH 3), 1 basic test tube (pH 10), and 1 neutral test tube (pH7) from your teacher. CAUTION: Do
not let acids or bases contact your skin or clothing.
2. Add 2 ml hydrogen peroxide to each of the 3 clean test tubes.
3. Add one piece of potato to each test tube.
4. Draw the data table below into your Data/Observations section. Record the rate of the reaction Reminder: 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).
pH
Rate of reaction
Acidic (pH 3)
Neutral (pH 7)
Basic (pH 10)
Analysis
Make two line graphs of your data for Part B and Part C. Be sure to have the following on your graphs:
1. Detailed title (includes both variables)
2. label each axis (with units)
3. Describe the trend underneath the graph. What is the graph showing? What does this mean about the effect of the
catalase on your tested variables?
4. USE A STRAIGHT EDGE OR COMPUTER GENERATED GRAPH.
Conclusion-Answer the questions about each test, then answer the remaining
questions about the lab as a whole.
Question for Part A
1a. What gas is being released?
2a. What reaction is happening in your test tube?
Questions for Part B
1b. Describe the 3 reactions.
2b. What is the optimal temperature for your catalase?
3b. Why did some reactions not work? What happen to the catalase during these reactions?
Questions for Part C
1c. Describe the 3 reactions.
2c. What is the optimal pH for your catalase?
3c. What is the effect of the low or high pH on the enzyme activity?
Additional Questions
1. Describe how the environmental factors used in this lab AND explain why they had an effect on the activity of the
enzyme catalase.
2. Explain similarities and differences between each of your graphs and explain the trend of the graph in relation to
how catalase activity was affected in each study. (What does the graph show about how pH and temperature effect
how fast the catalase worked?)
3. Research what the word “optimal” means. Describe what the “optimal” temperature and pH would have been for
both tests. Be sure to provide evidence based on your observations and graphs in each test.
4. Give at least 2 examples of why enzymes are important to the human body. You are encouraged to do further
investigation (research) on for this question. You may use the search tool on my website for good information.