Got Milk? …Need Lactaid®?
INTRODUCTION
Background Information: In this experiment we will investigate the action of the enzyme lactase. Lactase catalyzes the following reaction:
lactose (milk sugar) glucose+galactose
Glucose is absorbed across the wall of the digestive tract and delivered by the bloodstream to all of the body's cell for energy. Thus, lactose breakdown is an important reaction in nursing mammals, including human babies.
For our lab, the source of lactase enzyme will be Lactaid® caplets purchased from the drugstore. Lactaid®, a product of biotechnology, is marketed for people who are lactose intolerant. They can no longer digest foods containing lactose (milk, cheese, ice cream, etc.) because their bodies have stopped making the enzyme lactase. The undigested milk sugar in their digestive tract causes diarrhea or stomach upset. You probably know someone who is lactose intolerant; it is pretty common. The digestive systems of most races of people stop producing sufficient lactase in their late teens.
Problem: Is the enzyme lactase more effective at room temperature or at 37ºC?
Hypothesis:______
______
MATERIALS & METHODS
Materials:
4 test tubes
test tube rack
distilled water
nonfat milk
Lactaid® solution
labeling tape
stir rod
3 pipettes
warm water bath (37ºC)
4 Diastix glucose test strips
Method:
1.Label the 4 test tubes: "1", "2", "3", "4". In addition, on test tubes 3 and 4, put the initials of a group member so that you will be able to recognize those test tubes in a later step.
2.Prepare test tube 1 as follows:
30 drops nonfat milk
15 drops water
3.Prepare test tube 2 as follows:
30 drops nonfat milk
10 drops Lactaid® solution
5 drops water
4.Prepare test tube 3 as follows:
30 drops nonfat milk
15 drops water
5.Prepare test tube 4 as follows:
30 drops nonfat milk
10 drops Lactaid® solution
5 drops water
6.Using your thumb to cover each test tube, invert each test tube carefully to mix the contents.
7.Allow test tubes 1 and 2 to sit for 15 minutes at room temperature.
8.Place test tubes 3 and 4 in a warm water bath (37ºC) for 15 minutes.
9.While you wait, fill in Data Table 1 (all except the final column). Make predictions about what you will see when you test each solution with the glucose test strips!!
10.After 15 minutes, remove test tubes 3 and 4 from the water bath.
11.Test the contents of each test tube with a glucose test strip for the presence of glucose.
**The glucose test strips require 20-30 seconds after exposure to solution to show results.
12.Record your results in Data Table 1. (use "0" for no glucose, "+" for a small to medium amount of glucose, and "++" for a large amount of glucose.)
- Return all materials and clean up your lab station. Wash your hands.
Got Milk? …Need Lactaid®? – Student Answer Sheet
Problem: Is the enzyme lactase more effective at room temperature or at 37ºC?
Hypothesis: ______
______
RESULTS
Data Table 1
TUBE # / Contents of Tube / Storage Temperature (ºC) / Prediction glucose present?(yes or no) / Results: how much glucose
(0, +, ++)
1
2
3
4
DISCUSSION
1a. What kind of sugar is found in milk?
b. Is it a mono-, di-, or polysaccharide?
c. What is its chemical formula?
2a. Name the building blocks of milk sugar.
b. What are their chemical formulas?
3a. What is the name of the enzyme used in this experiment?
b. Is it a lipid, a protein, or a carbohydrate?
4a. Is this a hydrolysis or condensation reaction?
b. How can you tell?
5. What is the substrate in this experiment?
6a. Why did you test the glucose with the test strip?
b. Why did you test the lactaid?
7a. Does milk contain glucose?
b. How do you know?
8a. Does Milk + Lactaid contain glucose?
b. How do you know?
c. What does the presence of glucose prove?
10. Some people cannot drink milk because their digestive system does not produce lactase. When they eat a milk product or drink milk they get cramps, bloating, gas, and diarrhea. What could these people do in order to ingest milk products without these problems?
- Another way to denature (break apart or change the shape of) some enzymes is by lowering the pH of a solution. Would lowering the pH of the lactase solution affect the enzyme? (HINT: Lactase normally works in the highly acidic environment of the stomach.)
Why or why not?
12. Discuss how the manipulated variable (temperature) affects enzyme activity.