Modified by Jane Crumlish from the instructions on LACTAID®.
Updated: April 20, 2008
Type of Entry:
Type of activity:
- Hands-on activity
- Group/cooperative learning
Notes to the teacher:
Hands-on activities for the study of enzymes usually involve spit or
liver; the use of spit is not a good health practice and the students
find liver gross. The concept of the enzyme action gets lost in the
students' aversion to these enzyme sources. Lactaid-lactose has been
successful due to its simplicity. My favorite way to use it is as a
student demonstration. Several students do the activity and report to
the class on what is happening. We discuss as we progress and students
suggest various things to do; they make sure that each section has a
control. This activity has been conducted as a lab using paper models
of lactose and lactase. It has also been used successfully as a
cooperative learning exercise. The reaction rate is very fast when
using small amounts. Lactaid® does not denature. Changing the rate
of reaction and specificity are the properties best illustrated by
Required of students
Students should have
some knowledge of test papers and indicators. They should also have
some knowledge of carbohydrates.
Preparation time needed
Time is needed for shopping and the gathering of the materials.
The liquid Lactaid® can be stored in the refrigerator and will
last for several years for use in this laboratory. Glucose and sucrose
solutions can come from any source.
Class time needed
The minimum is approximately 20 minutes. More time is necessary if
paper models are used.
Students use a drop of milk, test it with
glucose test paper and establish that there is no glucose in milk.
Student also test glucose solutions to discover the color range of the
glucose test paper readings. Students test Lactaid® to establish
that it contains no glucose. Students mix Lactaid® and milk, use
the glucose test paper and discover the presence of glucose.
Paper models can be used to help students visualize
enzyme action. A disaccharide is used for lactose; a rectangle with
a piece fitting into the junction can be used for the enzyme.
- Spot plate or glass slide
- Toothpick for mixing
- Forceps for handling the
glucose test paper
- Milk-whole, skim or 1%
- Lactaid® (lactase source) the liquid form works best
- Glucose test strips (available from laboratory suppliers such as
Carolina Biological, Wards Scientific and others)
- Any glucose
- Any sucrose solution
- Paper models of enzyme, HOH,
galactose, glucose, lactose.
Download ready to print paper models.
You can tailor models to resemble your text visuals.
Most foods that are ingested are composed of
large, complex molecules. These molecules are not useful to the body
unless they are first broken down into small, simple molecules. The
act of breaking down large molecules into smaller ones is called
digestion. Digestion is dependent on various enzymes produced by the
organs of the digestive system to make the chemical activity of
hydrolysis occur in a reasonable amount of time. The puropse of this
activity is to work with models of substrates and enzymes; to test the
digestion of lactose with lactase; and to determine if digestion of
lactose has or has not occurred.
- active site
many sugar rings are there in lactose? Based on this classify
- Complete the following:
| Lactose or milk sugar ||
| Add water || +
| || ||
| Subtract Glucose formula ||
|| _____________________ |
| Galactose formula|| =
|| _____________________ |
What would be the enzyme that activates this reaction?
Where does this enzyme act in your body?
Where is this enzyme produced in your body?
Name the substrate.
PUT A STAR * ON THE
ACTIVE SITE OF THE LACTOSE MODEL. LABEL THE ENZYME MODEL BY NAME. Cut
out all the models along the exterior solid lines. Tape lactose,
water and enzyme models in the appropriate spaces (to be determined by
teacher). Cut along the dotted lines of the other two models; reverse
the procedure that you did for the dehydration synthesis to complete
DIGESTING LACTOSE WITH LACTASE
- Use the marker to
draw and number 4 circles on glass plate or slide. Use different
droppers for each solution and add the following:
Circle 1: add 2 drops of glucose solution
Circle 2: add 2 drops of milk
Circle 3: add 1 drop of lactase
Circle 4: add 1 drop of lactase plus 2 drops of milk (mix with toothpick)
- After 3 minutes, test each of the above for the presence of
glucose by dipping a piece of glucose test paper to each.
- After 2 minutes, note any color change in the glucose test paper.
- Record the data in table 1 and complete the table.
TABLE 1: RESULTS OF TEST FOR GLUCOSE
| Circle ||
Contents || Glucose test paper color ||Interpretation|
|| AFTER |
| 1 ||
Glucose || || ||
| 2 ||
Milk || || ||
| 3 ||
Lactase || || ||
| 4 || Lactase +
Milk || || ||
- In which circle would you expect the
hydrolysis of the milk sugar, lactose?
- What products would
result after this hydrolysis?
How did you know this?
- Why did you test the glucose with the glucose test paper?
Why did you test the lactase with the glucose test paper?
milk contain glucose?
What is your proof?
- Does milk
combined with lactase contain glucose?
What is your proof?
- Some people cannot drink milk because their digestive systems do
not produce lactase. If milk is ingested, it cannot be digested.
This results in cramping, bloating, gas, and diarrhea. Suggest a
treatment that would allow a person such as this to ingest milk.
Method of Evaluation/ Assessment
Students will answer the
above questions as they proceed through the activity
Reinforcement/ Additional Ideas
After students have done the
initial activity, have them design and execute labs to illustrate that
enzymes are specific and that enzymes are reusable.
are specific. Sucrose solutions can be used to show that the
lactase in the Lactaid will not break down sucrose.
- Enzymes are reusable. Students take a little of the Lactaid- milk
and add it to a new drop of milk. Some glucose test papers will turn
more intense shades with greater amounts of glucose.