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Name ____________________________Period _____Date______________________ Lab: Enzymes
This is an Informal laboratory that you will complete in your notebooks.
Pre-Lab
Within each human body cell, there are thousands of chemical substances called enzymes. These are
proteins, which means they are composed of chains of amino acids twisted and folded into weird shapes. How do
enzymes function? The answer is very complicated and some of the details are still unknown.
Enzymes are considered to be organic catalysts. A catalyst is a substance which speeds up a chemical
reaction. For example, the enzyme amylase (ptyalin), present in saliva, can break starch molecules into molecules of
the double sugar maltose. This transformation is accomplished very rapidly, at a relatively low temperature (body
temperature) and without the use of acids or other strong chemicals.
Amylase is thought to have an irregular surface because of the twisting and folding of its amino acid chain.
A starch molecule will fit into some of these irregularities as a key fits into a lock. A temporary union is formed
between the amylase and starch. This union is called an enzyme-substrate complex. The substrate is the substance
upon which the enzyme acts. After the formation of the complex, the enzyme acts in such as way as to split the
substrate molecule (starch in this case) into sugars. The sugars leave the surface rapidly and the enzyme is ready
to accept more substrate molecules immediately. Enormous numbers of such reactions can take place before an
enzyme molecule wears out. Enzymes can also work in the opposite way, bringing two molecules together so that
they can unite easily to form a new compound.
Most enzymes have names ending is ase. (Ptyalin is an exception.) The enzyme catalase is present in
almost every living cell. This means that there are billions of molecules of catalase in every human body. Why is
this?
During the process of cellular respiration, glucose is changed so that its chemical energy can be stored in
ATP. A by –product of these reactions is hydrogen peroxide H 2O2. This is the familiar antiseptic that can be
purchased at the drug store. In human cells, however, H2O2 is a poison. It is the function of catalase to break up
this toxic substance as it is made. The chemical equation for this reaction is 2 H2O2  2H2O + O2. Notice that
the products are water and oxygen, both of which are harmless.
In this lab, you will test samples of organic substances to detect the presence of catalase. If bubbles of
oxygen are released, you can assume that the H2O2 has been broken up and that catalase is present. Next, you will
see how catalase activity is affected by temperature and by acidity. You can determine the activity of the
catalase by observing how much bubbling takes place and how fast the reactions occurs.
Pre-Lab Questions:
1. Define the term “catalyst”.
2. What are the advantages of enzymes (organic catalysts) in chemical reactions?
3. To which group of organic substances do enzymes belong?
4. What is meant by the word “substrate”?
5. What is the usual suffix used in naming enzymes?
6. Why does the H2O2formed in cells have to be destroyed?
7. How can you detect the activity of catalase?
8. Research the role of ribozymes (RNA as enzymes).
Scientific Questions:
- Is peroxidase present in Avocado & what conditions can affect the reaction rate of an enzyme?
o Conditions: temperature, pH, enzyme concentration, substrate concentration
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Available Materials:
- Test tubes & racks, plastic trays, avocado, hydrogen peroxide buffer solutions (pHs: 3,5,7,9),
ice/refrigerator/freezer, hot plates, beakers, scales, graduated cylinders, knife, cutting board
Hypothesis:
Variables & Controls:
Independent Variables:
Dependent Variable:
Controls:
Constants (Confounding Variables):
Procedure:
In groups of 3-4 develop a procedure for testing your hypothesis & make your data tables.
Questions:
1. How did you determine that peroxidase was in the avocado?
2. Did pH and temperature affect the rate of enzyme reactions? Explain with your data.
3. What is indicated when perioxide bubbles are placed on an open cut?
Use the diagrams to answer question #6.
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25
Energy level
25
Energy level
20
15
10
20
15
10
5
5
0
0
1
2
3
4
Reaction rate
5
6
1
2
3
4
5
6
Reaction rates
4. The first graph shows the reaction rates and energy levels for Enzyme B. The graph to the right of it
shows the reaction rates and energy levels for the same reaction that occurred without the enzyme.
Which reaction required more “activation energy”?
5. At what temperature must enzymes work in our bodies? Explain.
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