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Biofuels Webquest: Got Milk?

Got Milk?



Do you know that some people can’t digest milk?  Many of you have most likely seen products being sold at the grocery store that say lactose free.  What is this sugar and why are some people lactose-intolerant?

What this enzyme called lactase and what does it have to do with lactose-intolerant? How does it work? Are you lactose-intolerant and how can you find out?




Lactose, the sugar found in milk, is a disaccharide composed of glucose and galactose (both six-carbon sugars). Sucrose, ordinary table sugar, is also a disaccharide composed of fructose and glucose. Glucose is a six-carbon sugar and fructose is a five-carbon 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. People who can digest or break down lactose are said to have Lactase persistence.


You will now watch this video on Lactase persistence.



After watching the video answering these questions:


1. What two monosaccharides (simpler sugars) are formed when the lactase enzyme hydrolyzes lactose?


2. True or False. “The genetic mutations that cause lactase persistence only occur in people living in pastoralist populations.” Justify your answer in one or two sentences.


3. True or False. “Geneticists studying the gene for lactase did not find any differences in the coding region DNA between people who could digest lactose and people who could not digest lactose.” Justify your answer in one or two sentences.


4. True or False. “Human evolution ended 200,000 years ago when humans (Homo sapiens sapiens) became a distinct species.” Justify your answer in one or two sentences.


5. All known mutations giving rise to lactase persistence occur in the genetic switch that regulates the expression of the lactase gene. What is the effect of these genetic switch mutations?


6. What would be the effect of a mutation in the coding region of the lactase gene?


7. Consider the diagram below. Each pie chart represents a unique population that was examined. The degree to which the pie chart is filled in illustrates the percentage of individuals in that population who are lactase persistent.



Identify two trends you see in the data. Provide evidence to support each trend.


State one possible hypothesis that can explain the global distribution of lactase persistence (lactose tolerance) and lactase nonpersistence (lactose intolerance). Be sure to include the following key words in your explanation: selection, fitness, survival.



Now you will go on an Internet search for information about lactose and lactase persistence.





After your research is completed you will now be working in groups in the lab.  Your team will experiment with the enzyme lactase.

Our source of lactase enzyme will be Lactaid caplets purchased at the drugstore.  Lactaid, a product of biotechnology, is marketed for lactose intolerant persons who suffer digestive problems  after eating or drinking foods that contain lactose (milk, ice cream, cheese, etc.).  You probably know someone who is lactose intolerant.  Your group can research in the lab any question you generate about the enzyme but your team should start with these first and then you can do independent research.


What is the rate of the enzyme lactase? Does temperature effect the rate?  Does pH effect the rate?  Does lactase speed up the break of other sugars such as sucrose ( table sugar)?


Helpful Hints:

Use Beakers and they should contain the same volume.


1.   Label your beakers. All beakers should contain the substrate lactose.

2.  The control should have no lactase solution.  All other beakers should.  The product of the          hydrolysis of lactose is glucose, which can be detected with test strips.

3.  Consider the effect of HCl and base, sodium bicarbonate solution.

4.  Consider the effect of temperature( cold–room-warm-hot ).

5.  Measure the glucose level in each beaker given the same amount of time.

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:
    • Place twenty milliliters of enzyme solution into a Pyrex test tube.
    • Add two hundred milliliters of water to a four hundred milliliters Pyrex beaker.
    • Place the test tube in the beaker (gently laying the test tube so it rests on the side of the beaker.)
    • Place the beaker and test tube on the hot plate.
    • Boil the water in the beaker for thirty minutes.
    • Let the solution cool to room temperature.


Experimental Design (Procedure)


  1. Gather the materials.
  2. Label the test tubes with the following labels:
    1. Test tube with skim milk and enzyme solution.
    2. Test tube with skim milk and water.
    3. Test tube with skim milk and denatured enzyme solution.
    4. Test tube with sucrose solution and enzyme solution.
    5. Test tube with sucrose solution and water.
  3. In test tube A add two milliliters of skim milk and one milliliter of enzyme solution.
  4. 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 B add two milliliters of skim milk and one milliliter of water.
  6. Repeat step 4.
  7. In test tube C add two milliliters of skim milk and one milliliter of denatured enzyme solution.
  8. Repeat step 4.
  9. In test tube D add two milliliters of the sucrose solution and one milliliter of enzyme solution.
  10. Repeat step 4.
  11. In test tube E add two milliliters of the sucrose solution and one milliliter of water.
  12. Repeat steps 4.

Results Section:

Construct a data table on the computer or iPad.  Then draw a graph showing the rate of the reaction verses temperature and pH


You can make this into a table with six rows by two columns. In the second column, record if the glucose test is positive or negative.


Glucose Presence in the Following Solutions

Type of Solution

Positive or Negative Glucose Result

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




Conclusion and questions


  1. Diagram and describe the lactose and lactase reaction.
  2. Why did the enzyme react to lactose but not to sucrose?
  3. What happened when the enzyme was boiled?
  4. 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?
  5. What type of reaction is this? Dehydration or hydrolysis?

Remember your group can research in the lab any question you generate about the enzyme and you can now do independent research.

Subject Guide

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Jennifer Jourdain
Montachusett Regional Voc Tech School
1050 Westminster Street
Fitchburg, MA 01420
(978) 345-9200 x5125