Enzyme Lab - Teacher Guide
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 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: The chemicals can be purchased from chemical or biological supply companies, students should wear safety goggles This lab requires some set up and can be messy. Not advised unless you actually have a lab to work within. There is an alternative lab that uses a website at enzymelabweb.html
| 1molar HCl solution (in dropper bottle) 1molar NaOH solution (in dropper bottle) 6 Test tubes Measuring Pipette |
10-ml Graduated cylinder |
Thermometer |
|
PART A - Observe Normal Catalase Reaction
1. Place 2 ml of the 3% hydrogen peroxide solution into a clean test tube.
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? ___from the equation above, oxygen is being released_____
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 _____warmer_____
Is the reaction endothermic or exothermic? ___exothermic____________
Is Catalase Reusable?
3. Pour off the liquid into a second test tube. Assuming the reaction is complete. What is this liquid composed of? __water_____
What do you think would happen if you added more liver to this liquid? __no reaction, peroxide is already broken down______
Test this and record the reaction rate. Reaction Rate _____1___ (1 – 5)
4. Add another 2 ml of hydrogen peroxide to the liver remaining in the first test tube. What is the reaction rate? ___4-5____
Is catalase reusable? Explain. ________the catalase in the liver will contine to break down peroxide as long as you keep adding peroxide________________________
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 |
answers vary, all of these will have some reaction |
Apple |
|
Chicken |
|
Which tissues contained catalase? _________animal tissues contain catalase, chicken greatest reaction__________________
Do some contain more catalase than others? How can you tell? ________more bubbles_____________________
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. What will boiling do to an enzyme? ________denatures it, makes it not work_________________
2. 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? ___0-1___
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 each of the following water baths: Ice bath and 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? _3-4__
What is the reaction rate for the warm liver/peroxide? _4-5____
PART D - What is the Effect of pH on Catalase Activity
1. Add 2 ml hydrogen peroxide to each of 5 clean test tubes.
Tube 1--add 3 drops of HCl (acid) Tube 2 - dilute HCl (1 drop / 3 ml) – add 3 drops *Use pH paper to determine the exact pH |
Tube 3 – add 3 drops of NaOH (Base) |
Now add liver to each of the test tubes (best to do it all at the same time so reaction rates can be observed at the same time)
Rate of Reaction for Strong Acid _____ Acid _____ Neutral ______Strong Base_____ Basic _____
*If needed you can raise your rating scale to 6
What is the optimal pH for catalase (estimate)? _______answers vary here, most students report that the catalase works best in the acidic solution________
DATA ANALYSIS
Describe in a short paragraph (on a separate page). Attach the analysis to this page.
- describe the reaction and how you measured reaction rate
- how temperature and pH affect the actions of the enzyme catalase, and why these elements affect the reaction rates
- how you would determine the optimal temperatures and pH of an enzyme, propose a new experiment
- how this experiment can apply to the real world
RUBRIC (I also have them turn in this page)
| 1 | 2 | 3 | |
| Intro: description of reaction and how rates were determined (bubbling) | |||
| Accurately describes how temperature can affect the reaction rate of catalase, includes discussion or mention of denaturing at boiing | |||
| Discusses pH and its affect on the reaction rate, includes an answer regarding optimal pH | |||
| Proposes a further experiment that would determine the exact optimal pH and temperature | |||
| Explain how enzymes are used by animal tissues to break down harmful chemicals or invaders | |||
| Total | |||