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What factors affect enzyme activity?
Please do not remove from class.
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. The reaction looks something like the diagram below. Notice how the shape of the enzyme and the
shape of the substrate (the chemical it is acting upon) fit together! That turns out to be very important…
Each one of those hundreds of enzymes in your body 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 of animals, plants, even fungi! 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: 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.
The rate of the catalyzed breakdown of hydrogen peroxide can be measured by the rate of O2 production. The faster the
breakdown of H2O2, the faster oxygen bubbles form. In this investigation the speed with which O2 bubbles cause a paper
disk to rise indicates the relative speed of the reaction. Your source of the enzyme will be liver cells.
Experiment I. Procedure
1. Use a hole punch to make a disk of filter paper. You will need several disks. Keep them clean and dry before use!
2. Drop the filter paper disk into a bowl with some of the liver solution. Let the disk soak for 5 seconds.
3. Pour _____ mL of one of the hydrogen peroxide solutions into the small cup.
4. Using tweezers, touch the edge of the paper disk on a paper towel for 5 seconds to remove excess liquid. Move the
filter paper disk into the bottom of the hydrogen peroxide cup. BEGIN TIMING THE MOMENT THE DISK ENTERS
5. The disk will eventually float to the surface as it fills with O2 bubbles produced by the breakdown of H2O2.
Sketch labeled set-up
in journal under
6. Stop timing when the disk reaches the surface.
7. Measure the total distance in mm the disk travels.
Note: for some of the trials, the disk may not reach the bottom of the cylinder!
Note: total distance is distance the disk travels down AND back up!
8. Record the time in seconds.
9. Calculate rate as mm/s.
10. Repeat steps 1-9 for the other trials.
11. Record and average your results.
Report Average for Class Data.
Experiment II. Procedure
You will be assigned a treatment for the enzyme catalase. We will look at how temperature and pH affect the ability of
catalase to work on hydrogen peroxide (H2O2). Follow the same procedures above AFTER the enzyme is treated.
For Boiling: Use a catalase solution that has been boiled for 5 minutes.
For Ice Cold: Use a catalase solution that has been kept at 0C for 5 minutes. KEEP THE ENZYME ON ICE WHILE
For Acid: Use a catalase solution that .1M HCl has been added to. Use a pH strip to get the pH of the solution.
SAFETY: Wear goggles when using the acid-catalase solution!
For different tissues: record which solutions you use.