Name: _____________________________
Date: ____________
Period: _________
ENZYMES LAB
Enzymes Help Us Digest Food1
Introduction to Sugars and Enzymes
PRELAB:
The food we eat contains many different types of molecules, including two types of sugars:
monosaccharides and disaccharides. For example, fruits contain the monosaccharides, glucose
and fructose, and the disaccharide, sucrose.
★1. In the diagrams below: - circle the name of each monosaccharide
- use arrows to indicate the names of the disaccharides.
★2. What is the difference between a monosaccharide and a disaccharide?
Monosaccharides from the food you eat are absorbed from your gut into your blood and carried
to all the cells in your body where they are used for energy. Each disaccharide molecule must be
broken down or digested into its monosaccharide components before it can be absorbed into the
blood.
★3. When a sucrose molecule is digested, which monosaccharides are produced?
The digestion of the disaccharide lactose to the monosaccharides glucose and galactose occurs
very very slowly unless there is an enzyme to speed up the process. The enzyme that speeds up
the digestion of lactose is called lactase.
1
Partially adapted from “Lactase Investigation” in the School District of Philadelphia Biology Core Curriculum, by Drs. Ingrid Waldron and
Jennifer Doherty, Department of Biology, University of Pennsylvania, © 2012. Teachers are encouraged to copy this Student Handout for
classroom use. An alternative version, Word files (which can be used to make changes if desired), Teacher Preparation Notes, comments, and
links to our other hands-on activities are available at http://serendip.brynmawr.edu/sci_edu/waldron/ , with additional activities available at
http://serendip.brynmawr.edu/exchange/bioactivities .
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Lactase and most other enzymes are proteins. Each enzyme has an active site where a substrate
molecule binds. For example, the substrate lactose binds to the active site of the enzyme lactase.
Notice that the name of the enzyme lactase was created by adding the suffix –ase to part of the
name of the substrate lactose.
★4. Circle the active site in the enzyme in the figure above.
An enzyme speeds up a chemical reaction which converts a substrate or substrates to a product
or products. The products are released from the enzyme and the enzyme returns to its original
state, so the enzyme is ready to act on another substrate molecule. Thus, an enzyme molecule
can be reused over and over. For example, a single molecule of the enzyme lactase can speed up
the digestion of many, many molecules of lactose.
★5. The following equation shows the digestion of lactose.
Lactase
Lactose --------- > Glucose + Galactose
Use E to indicate the enzyme, S to indicate the substrate, and P to indicate the products. Circle
the molecule that is a protein, and use arrows to indicate the molecules that are sugars.
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LEARNING OUTCOMES:
This lab will examine the specificity of an enzyme to a specific substrate. Students will also
observe what will happen when the enzyme is denatured.
MAT E RI AL S / RE SO URCE S :
 Lactase tablets.
 Fifteen milliliters of milk.
 Water.
 Sucrose.
 Graduated cylinder.
 Three four hundred milliliter
beakers: used for dissolving the
lactase tablet, dissolving the sucrose
and boiling the lactase.
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Five test tubes.
Test tube rack.
Marking pencil OR labels for test
tubes.
Hot plate with a Pyrex test tube for
denaturing the enzyme.
Glucose test strips.
Stirring rod.
PU R PO S E :
This lab will examine the specificity of an enzyme to a specific substrate. Students will observe
what happens when the enzyme is denatured.
I NT RO DUCT IO N :
Lactose, the sugar found in milk, is a disaccharide composed of glucose and galactose
(both six-sided sugars). Sucrose, ordinary table sugar, is also a disaccharide composed of
fructose and glucose. Glucose is a six-sided sugar and fructose is a five-sided sugar.
Lactase is an enzyme that breaks lactose down into galactose and glucose. Lactase can be
purchased in pill form by people who are lactose intolerant. These people lack the enzyme,
lactase, and cannot break down the sugar lactose into its component parts.
Although lactose is similar to sucrose, lactase will break down only lactose because of the
shape of the sugar.
In this lab, you will see lactase break lactose down into galactose and glucose. You will also
observe what happens if the shape of lactase is changed due to heating.
PRO CE DU RE S :
Solution preparation
1. Enzyme solution: Add one lactase tablet to two hundred milliliters of water. Stir until the
tablet has dissolved.
2. Skim milk: this solution contains the lactose.
3. Sucrose solution: Add five grams of sugar to one hundred milliliters of water. Stir until
the sugar has dissolved.
4. Denatured enzyme solution:
o Place twenty milliliters of enzyme solution into a Pyrex test tube.
o Add two hundred milliliters of water to a four hundred milliliters Pyrex beaker.
o Place the test tube in the beaker (gently laying the test tube so it rests on the side
of the beaker.)
o Place the beaker and test tube on the hot plate.
o Boil the water in the beaker for thirty minutes.
o Let the solution cool to room temperature.
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Lab procedures
1. Gather the materials.
2. Label the test tubes with the following labels:
A. Test tube with skim milk and enzyme solution.
B. Test tube with skim milk and water.
C. Test tube with skim milk and denatured enzyme solution.
D. Test tube with sucrose solution and enzyme solution.
E. Test tube with sucrose solution and water.
3. In test tube A add two milliliters of skim milk and one milliliter of enzyme solution.
a. Time for two minutes and test for glucose with the glucose test tape. Record this
data in table 1. If there was glucose present mark a ‘+’ in the table. If glucose was
absent, mark a ‘-’ in the table.
4. In test tube B add two milliliters of skim milk and one milliliter of water.
a. Time for two minutes and test for glucose with the glucose test tape. Record this
data in table 1. If there was glucose present mark a ‘+’ in the table. If glucose was
absent, mark a ‘-’ in the table.
5. In test tube C add two milliliters of skim milk and one milliliter of denatured enzyme
solution.
a. Time for two minutes and test for glucose with the glucose test tape. Record this
data in table 1. If there was glucose present mark a ‘+’ in the table. If glucose was
absent, mark a ‘-’ in the table.
6. In test tube D add two milliliters of the sucrose solution and one milliliter of enzyme
solution.
a. Time for two minutes and test for glucose with the glucose test tape. Record this
data in table 1. If there was glucose present mark a ‘+’ in the table. If glucose was
absent, mark a ‘-’ in the table.
7. In test tube E add two milliliters of the sucrose solution and one milliliter of water.
a. Time for two minutes and test for glucose with the glucose test tape. Record this
data in table 1. If there was glucose present mark a ‘+’ in the table. If glucose was
absent, mark a ‘-’ in the table.
RE S UL T S :
Glucose Presence in the Following Solutions
Positive or Negative Glucose
Result
Type of Solution
Test tube A: milk and enzyme solution
Test tube B: milk and water
Test tube C: milk and denatured enzyme solution
Test Tube D: sucrose solution and enzyme solution
Test Tube E: sucrose solution and water
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CO NCL US IO N AND Q UE S T IO NS :
1. Diagram and describe the lactose and lactase reaction.
2. Did lactase break down sucrose? How do you know?
3. Why did the enzyme react to lactose but not to sucrose?
4. Your results illustrate a general principle called enzyme specificity. Enzymes act only
on specific substrates. In many cases an enzyme can only react with a single kind of
substrate. For example, lactase can digest lactose, but not other types of disaccharide
sugars. Which part of an enzyme is responsible for this enzyme specificity? (Hint: See
the bottom of page 1.)
5. Because of enzyme specificity, our bodies need lots of different enzymes to digest
different types of food molecules. For example, our small intestine has the enzyme
lactase to digest lactose and a different enzyme to digest sucrose. What do you think is
the name of the enzyme that digests sucrose? (Hint: See the bottom of page 1.)
6. Complete the following equation to show the digestion of sucrose. Include the enzyme
and the products.
Sucrose ---------- >
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7. What happened when the enzyme was boiled?
8. Another way to affect the enzyme is by lowering the pH of the solution. However, lactase
is supposed to be able to work in the stomach. Would lowering the pH of the enzyme
solution affect the enzyme? Why or why not?
9. What type of reaction is this? Dehydration or hydrolysis?
10. Conclusion:
What were the main points you took away from this lab (Why do you think we conducted
this lab?)
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