Ready:
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?
http://www.hhmi.org/biointeractive/media/lactose_digestion-sm.mov
Set:
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.
http://media.hhmi.org/fittest/Got_Lactase.html
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.
http://www.teachersdomain.org/asset/tdc02_vid_ruminant/
Go:
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.
http://www.lactaid.com/products/fast-act-caplets
Questions:
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.
Experimental Design (Procedure)
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 |
|
Remember your group can research in the lab any question you generate about the enzyme and you can now do independent research.