Enzymes
Adapted from Air All Around: Oxygen Investigation
Author: Doris Pun & Brittland DeKorver
Institute for Chemical Education and Nanoscale Science and Engineering Center
University of Wisconsin-Madison
Purpose: To learn about enzymes
Learning Objectives:
1. Learn what an enzyme is and what it does.
2. Observe an enzyme in action.
3. Learn how enzymatic activities can be altered.
Next Generation Science Standards (est. 2013):
 PS1.A: Structure and Properties of Matter (partial)
 PS1.B: Chemical Reactions
 PS3.B: Conservation of Energy and Energy Transfer (partial)
National Science Education Standards (valid 1996-2013):
 Standard B: Physical Science
o Properties and changes in properties of matter
o Transfer of energy
 Standard C: Life Science
o Structure and function of living systems
o Regulation and heredity
 Standard D: Science and Technology
o Abilities of technological design
o Understanding about science and technology
 Standard F: Science in Personal and Social Perspectives
o Science and technology in local, national, and global challenges
Suggested Previous Activity:
Green Chemistry: Catalysts
Grade Level: 5-8
Time: 60 minutes
Materials:
 20-30 coins/caps
 Timer
 Tennis ball or similar sized
ball
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Safety glasses
Gloves
3 % hydrogen peroxide (H2O2)
13 mL test tubes
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Cut potatoes (0.5 x 0.5 x 2 cm
sticks)
o Raw, boiled, frozen
Dilute acid (0.1M HCl)
Dilute base (0.1M NaOH)
Pipettes
CuSO4
Spatula
Apples
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Knife
Petri dishes
Lemon juice
Microscopes
Microscope slides of different
enzymes
Yeast
Safety: Wear gloves and safety goggles while handling the peroxide, liquid
nitrogen, acid and base solutions.
Preparation ahead of time:
Prepare small bottles of 3 % H2O2 for student use. Cut the potatoes into
approximately identical sizes, 0.5cm x 0.5cm thick and 2-3cm long. Boil 1/6 of the
potatoes.
Definitions:
- Enzyme: catalyst that helps perform a chemical reaction within living
cells/organisms
- Substrate: the molecule that the enzyme alters
- Product: the molecule that the enzymes produce from the substrate
- Active site: site within the enzyme that the substrate binds to and the chemical
reaction occurs
- Inhibitor: molecules that bind to the active site of an enzyme in such as way that
prevents substrates from binding
Introduction:
Catalysts are substances that speed up a chemical reaction without being
consumed in the reaction, making it reusable. Catalysts are used to make many
plastics and medicines, and biological catalysts (enzymes) perform all sorts of
important reactions in our bodies. They are usually made up of large proteins or
polymer chains. In a typical enzyme-catalyzed reaction, a specific molecule
called the substrate binds to the enzyme in a pocket specifically designed for the
molecule called the active site. The enzyme then converts the substrate into one
or multiple products and releases the product. The enzyme can then bind
another molecule and repeat the reaction.
Any changes to an enzyme’s active site will affect the catalytic efficiency of the
enzyme. A common change is the denaturing of the proteins, where the shape
and structure of the proteins are lost. A familiar example is the denaturing of egg
whites when cooking/heating. Another familiar example is the addition of vinegar
(an acid) to milk causing it to curdle. These examples demonstrate that the
temperature and acidity can cause denaturation. The enzymatic efficiency can
also be affected by the presence of inhibitors. Inhibitors bind to the active site,
stopping the substrate from entering the active site so that the chemical reaction
can occur. Many drugs are actually inhibitors, working by inhibiting enzymes in
bacteria, viruses, or cancerous cells.
Tell the students that today they are going to learn about enzymes and they are
going to explore several enzymes in action. They will also learn how to alter an
enzyme’s activity.
Procedures:
1. Enzyme Models – fingers catalyzed reaction (Group activity)
a. Special role - rotate amongst the students
i. Timer – will measure how long the reaction takes to reach
completion
b. Explain to the students that the reaction is flipping all the caps/coins
such that they are all either heads/bottoms up
c. Normal enzymatic reaction: (perform 4-10 times total)
i. Explain that the students are “enzymes” and can use all
their fingers to do the reaction
ii. Time and record on a table datasheet how long it takes for
student #1 to flip all heads up
iii. Repeat step iii with student #2 for tails up
iv. Repeat steps iii-iv at least another round with different
students
v. Calculate the average enzymatic reaction completion time
d. Partial denaturing/decomposition of enzyme reaction
i. Explain that the enzymes are now slowly decomposing
either by high temperatures, acid or base contact, etc.
ii. Now the students are only allowed to use their 2 index
fingers to do the reaction
iii. Repeat Steps c. ii-v.
e. Enzyme inhibition reaction – select only one student to perform
i. Explain that the enzymes will now be introduced to
inhibitors
ii. Place a tennis ball into the palms of each enzyme’s hand
iii. Repeat Steps c. ii & v.
f. Discuss and compare the different conditions of each reaction
along with their reaction rates.
2. Lemon Juice Inhibition of Apple Browning
a. Have an adult slice up enough slices to give each student 2 small
slices
b. Put slices on separate Petri dishes and clearly label one as “lemon”
and the other as “no lemon”
c. Squeeze and rub lemon juice on the “lemon” slice
d. Set aside for 15 minutes and observe any differences between the
two slices
3. Potato (enzyme = catalase) Catalyzed Decomposition of Peroxide (H2O2)
into Water and Oxygen – wear safety goggles and gloves
This activity should be familiar to the students who performed the
manganese dioxide, MnO2, catalyzed peroxide decomposition reaction in
Green Chemistry: Catalysts.
a. Fill a test tube half way with peroxide, H2O2
b. Carefully drop a small stick of raw potato into the test tube
c. Record any observations, ie. bubbling, temperature of reaction?
d. Repeat with different conditions to try to inhibit/denature enzyme.
Suggestions:
i. Boiled potato stick
ii. Frozen potato stick
iii. With dilute acid (0.1M HCl)
iv. With dilute base (0.1M NaOH)
1. tip: add acid/base to potato first
v. With copper sulfate, CuSO4, as inhibitor
1. tip: measure out 400 – 500 mg CuSO4
2. coat potato with as much of the measured out CuSO4
3. put rest of the CuSO4 in the test tube of peroxide and
mix
4. drop CuSO4-coated potato in the test tube
4. (Optional if microscope available) Microscope Activity
a. Look at different prepared enzymes on slides
b. Observe yeast or potatoes with drop of peroxide
Discussion:
Ask students if they are familiar with hydrogen peroxide. Tell them that it is
commonly found in medicine cabinets. It works as an antibacterial agent as it can
destroy cells. It is also a common byproduct in metabolism in living organisms.
Tell them that hydrogen peroxide has two oxygen atoms in each hydrogen
peroxide molecule, and that the molecules break down. The atoms rearrange into
oxygen gas and water. The process will happen faster if an enzyme, like
catalase, is used. Catalase is an enzyme found in most organisms to rapidly
perform this decomposition reaction by binding peroxide and releasing oxygen
and water. High concentrations of catalase are found in the liver. Potatoes are
the source of catalase in this lesson. The boiling, lowered and elevated acidity by
adding acid and base, respectively denature the enzyme and lower the enzyme’s
efficiency. The freezing of the enzyme only denatures the enzyme partially. The
copper sulfate serves as a noncompetitive inhibitor to catalase, binding to the
enzyme’s active site and not allowing for peroxide to bind.
Apples and bananas contain an enzyme called catechol oxidase which catalyzes
the reaction of the compound, catechol, and oxygen to a new molecule called
benzoquinone, which is orange in color and also toxic to bacteria, slowing down
the spoilage of the fruit. Adding lemon juice, which is an acid, lowers the acidity
of the apple and denatures the catechol oxidase enzyme, preventing the
transformation, which causes the orange-brown color on apples.
Evaluation:
What is a catalyst?
Are catalysts usually consumed in a chemical reaction?
What is the relationship between catalysts and enzymes?
Do you think your body has some enzymes? Why or why not.
This lesson is the product of the Institute for Chemical Education and the
Nanoscale Science and Engineering Center at the University of Wisconsin-Madison.
This Material is based upon work supported by the National
Science Foundation under grant number DMR-0425880.
SCIENCountErs Lessons are licensed under a Creative Commons AttributionNonCommercial 4.0 International License. Permissions beyond the scope of this license may
be available by emailing ice@chem.wisc.edu.