This lab will examine the specificity of an enzyme (lactase) to a specific substrate (lactose). Students will observe the actions of the enzyme and how shape is important to enzyme reactions. Background information: Lactose, the sugar found in milk, is a disaccharide composed of glucose and galactose (both six-sided 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.
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. In this lab, you will see lactase break lactose down into galactose and glucose. You will also observe what happens if the shape of lactase is changed due to heating. Materials/ resources: * Lactase tablets: these can be bought in any drug store or grocery store.
Fifteen milliliters of milk: any milk will work. Water: used for dissolving the lactase tablet, dissolving the sucrose and boiling the lactase. * Sucrose: five grams per group. * One hundred milliliter graduated cylinder/ten milliliter graduated cylinder: measuring water and enzyme amounts. * Three four hundred milliliter beakers: used for dissolving the lactase tablet, dissolving the sucrose and boiling the lactase. * Five test tubes: these tubes hold the different solution mixtures. * Test tube rack: hold the test tubes. * Marking pencil: mark the test tubes so that confusion does not occur. * Clock * Hot plate with a Pyrex test tube for denaturing the enzyme. Glucose test strips: these strips can be found in any drugstore.
Stirring rod: helps to mix up the lactase tablet in the water. Lab procedures: 1. Gather the materials. 2. Label the test tubes with the following labels: 0 A. Test tube with skim milk and enzyme solution. B. Test tube with skim milk and water. C. Test tube with skim milk and denatured enzyme solution. D. Test tube with sucrose solution and enzyme solution. E. 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: 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 (may need to research this). 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? Content to be covered in conclusion paragraphs: It should explain the general conclusions of the lab. May refer back to background information to help explain the conclusion of the lab. Should refer back to the GENERAL data in the results. Restate the purpose and state whether the hypothesis was correct or not and why. Clearly state and explains how at least THREE errors may have occurred in the lab. Also explains common pitfalls a person SHOULD avoid.