Download Catalase Lab How do enzymes work in living tissues? Introduction

Catalase Lab
How do enzymes work in living tissues?
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 chemical. 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; 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. 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.
Part 1: Normal Catalase Activity
1.
Place 2 mL of 3% hydrogen peroxide solution into a clean test tube.
Is the hydrogen peroxide bubbling? Yes or No
(circle one)
2. Using forceps and scissors, cut a small piece of liver and add it to the tube. Push it into the
hydrogen peroxide with a stirring rod.
Observe the bubbles. What gas is being released?____________________________
3. Feel the temperature of the tube with your hand.
Has it gotten warmer or colder?
Warmer
/
Colder (circle one)
4. Pour the liquid from this tube into a second tube.
What is this liquid composed of? _______________________________
What do you think if you added more liver to this liquid? Why? _________________________
______________________________________________________________________________
______________________________________________________________________________
5. Add another 2 mL of hydrogen peroxide to the liver remaining in the first tube.
Can you observe any reaction? If so, what happens? ___________________________________
______________________________________________________________________________
What do you think would happen if you poured off this liquid and added more hydrogen
peroxide to the remaining liver?____________________________________________________
______________________________________________________________________________
Are enzyme reusable? Yes
or
No
(circle one)
Part 2: Catalase Inquiry
Enzymes are unique three-dimensional structures. The active site is the portion of the enzyme that
interacts with the substrate, so that any substance that blocks or changes the shape of the active site
affects the activity of the enzyme. A description of several ways enzyme action may be affected follows:
a. Salt Concentration: If the salt concentration is close to zero, the charged amino acid side chains
of the enzyme molecules will attract each other. The enzyme will denature (change shape). If,
on the other hand, the salt concentration is very high, normal interaction of charged groups will
be blocked, new interactions will occur, and again the enzyme will change shape. An
intermediate salt concentration, such as that of human blood (0.9%) or cytoplasm, is the
optimum for many enzymes.
b. pH: pH is a measure of acidity, or H+ concentration, in a solution. The scale runs from 0 to 14
with 0 being the highest in acidity and 14 the lowest. A pH of 0 to 7 is considered acidic. A pH of
7 to 14 is considered basic. Altering pH can affect the shape of the enzyme. Most enzymes
perform best at a neutral pH and are denatured if the pH is increased or decreased by too much.
Some enzymes, such as pepsin, which actin the human stomach where pH is very low, have a
low pH optimum.
c. Temperature: Chemical reactions tend to speed up as temperature increases. Each enzyme has
an optimum temperature at which it works best. Temperatures that exceed the optimum tend
to denature the enzyme and render it nonfunctional.
Other items can affect the rate at which the enzyme-catalyzed reaction takes place are as follows:



concentration of enzyme
concentration of substrate
source of enzyme (organism)
The rate of a chemical reaction may be studied in a number of ways including the following:



measure the rate of disappearance of substrate (H2O1 in this experiment)
measure the rate of appearance of product (O2 which is given off as a gas in this experiment)
measuring the heat released (or absorbed)during the reaction
Designing and Conducting Your Investigation
You now have the basic information and tools needed to explore enzymes in more depth on your own.
In this part of the lab, you will do just that. You will have the chance to develop and test your own
hypotheses about enzyme activity. Afterward, your lab group will create a mini-poster and share your
experiment with the class.
1.
What question would you like to ask about enzymes?
______________________________________________________________________________
2. Create a hypothesis for your question. Include the independent variable, dependent variable
and a prediction in your hypothesis. Give an explanation of your prediction. (If…. Then…
Because)
______________________________________________________________________________
______________________________________________________________________________
3. Identify the following parts of your experiment:
 Independent Variable:_____________________________________________________

Dependent Variable:_______________________________________________________

5 constants:______________________________________________________________
________________________________________________________________________
________________________________________________________________________
4. List the materials that you will use:
5. Outline the procedure that you will follow:
6. Create a data table for your results:
7. Document qualitative observations:
8. Graph your data:
9. Draw conclusions:
10. Create a mini-poster (see example).