Name________________________________
Block____________________
Date_________
Lactase Enzyme Lab
Background: Lactose, the sugar found in milk, is a disaccharide composed of glucose and galactose (both sixsided 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. Enzymes are responsible for
speeding up reactions. 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 is component parts.
Hypothesis: In the space below, provide what you think will happen when lactase is mixed with milk, boiled and
mixed with the sugar sucrose. (Basically, do you think the enzyme will still work?)
Milk:_______________________________________________________________________________________
________________________________________________________________________________________
Boiled: _____________________________________________________________________________________
______________________________________________________________________________________
Sucrose: ____________________________________________________________________________________
______________________________________________________________________________________
Procedure for Solution Preparation:
1. Plug in and turn on the hot plate to a setting of 3.
2. Place 200 milliliters of water into a large Beaker and place the Beaker in the center of the hot plate.
3. Add one lactase tablet to a separate beaker filled with 200 mL of water (not the one on the hot plate).
Stir until the tablet has dissolved. This may take a few minutes (be sure the entire tablet is dissolved
before you move on to the next step).
4. Place 20 mL of the enzyme solution created in step one into a clean test tube.
5. Place the test tube in the beaker on the hot plate (gently laying the test tube so it rests on the side of
the beaker).
6. Turn the hot plate up to a setting of 6.
7. After 30 minutes, turn off the hot plate ad take the test tube out of the beaker using tongs.
8. Place the test tube in a new beaker filled with 300mL of cold water and allow the solution to cool for
minutes.
9. While your solution cools, complete step 1 of the procedure below.
Procedure for Testing Enzymes:
1. Label 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 boiled enzyme solution
D. Test tube with sucrose solution and enzyme solution
E. Test tube with sucrose solution and water
2. In test tube A, add 2 mL of skim milk and 1 mL of enzyme solution (not the boiled one).
3. After 2 minutes, test for glucose with a glucose test strip. Let strip sit for 3 minutes before reading.
Record this data in the table you created in your research notebook.
4. In test tube B, add 2 mL of skim milk and 1 mL of water.
5. Repeat step 3.
6. In test tube C, add 2 mL of skim milk and 1 mL of boiled enzyme solution.
7. Repeat step 3.
8. In test tube D, add 2 L of sucrose solution and 1mL of enzyme solution (not boiled one)/
9. Repeat step 3.
10. In test tube E, add 2 mL of the sucrose solution and 1 mL of water.
11. Repeat step 3.
Post-Lab Questions
1. Why do you think the enzyme reacted to lactose but not sucrose?
_____________________________________________________________________________________
_____________________________________________________________________________________
2. What happened when the enzyme was boiled?
_____________________________________________________________________________________
3. Were there any parts during the lab where error may have resulted? What were they?
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
This assignment will be your first research assignment of the school year. Although you will be working with a
group in class to complete the lab, you will be required to complete the writing portion of the assignment on
your own.
Results:
1. Create a table to illustrate all of the data that you have collected from this lab. Be sure that your table is
labeled properly, contains units if necessary, has a formal title, and has a caption. A caption is just a 1-2
sentence summary of the information in the table.
2. Write out what your data shows. Do not add any analysis or explanation to your data. Just describe in
words what the table reveals. This is probably not going to be more than 3-4 sentences.
Discussion: Use the questions below to guide you in writing your discussion. Be sure to answer them as they
relate to what you did in the lab.
1. Why did each test tube not provide a positive result for glucose?
2. Why did the enzyme solution that was boiled provide no reaction?
3. Why did the solutions mixed with water provide no reaction?
4. How does an enzyme know what it should bond with?
5. What types of things can prevent an enzyme from functioning properly?
6. Were your initial hypotheses supported or not supported? Why or why not?
7. Were there any sources of error?