Name Date Block. Lactase Lab. (Adapted from Lactase Investigation Philadelphia Public Schools and Enzymes Help Us Digest Food from Bryn Mawr)

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1 Name Date Block Lactase Lab (Adapted from Lactase Investigation Philadelphia Public Schools and Enzymes Help Us Digest Food from Bryn Mawr) BACKGROUND INFORMATION: The food we eat contains many different types of molecules, including monosaccharaides and disaccharides. Two examples of disaccharides are sucrose and lactose. Sucrose is commonly called table sugar and is made up of glucose and fructose. The disaccharide lactose is made up of glucose and galactose. Monosaccharide molecules like glucose move from the inside of the small intestine where food is digested to the blood which carries sugar molecules to the cells of your body where they can be used for energy. Each disaccharide molecule must be broken down and digested into its monosaccharide components before it can move from the small intestine to the blood. For example, sucrose is digested to glucose and fructose, which can be absorbed into your blood and carried to all the cells in your body. The digestion of lactose occurs very, very slowly unless there is an enzyme to speed up the process. The enzyme that speeds up the digestion of lactose is called lactase. Lactase and most other enzymes are proteins. Each enzyme has an active site where a substrate molecule binds. For example, the substrate lactose binds to the active site of the enzyme lactase. The enzyme increases the speed of a chemical reaction, which converts a substrate or substrates to a product or products. The products are released from the enzyme and the enzyme returns to its original shape so the enzyme is ready to act on another substrate molecule. Thus, and enzyme molecule can be reused over and over. For example, a single molecule of the enzyme lactase can speed up the digestion of many molecules of lactose. The following equation shows the digestion of lactose. Lactose Lactase Glucose + Galactose N.Berg, NNHS, Page 1 of 7

2 PRE-LAB QUESTIONS: Question 1: What is the difference between a monosaccharide and a disaccharide? Question 2: When a lactose molecule is digested, which monosaccharaides are produced? PURPOSE: In this lab, we will answer the following questions: Can the sugar lactose be digested without any enzyme? What is a scientific control? Can the same enzyme digest lactose and sucrose? Do we need the enzyme lactase to digest milk? Experiment 1 In this experiment, you will test whether the enzyme lactase is needed to digest the sugar lactose. First, predict what you think will happen Lactose with no enzyme: Lactose with enzyme lactase: To test whether your predictions are correct, you will use glucose test strips to test whether glucose has been produced. A yellow square color means no glucose and shades of green means glucose is present. 1. Label a plastic cup: LACTOSE 2. One group member should measure 10 ml (~ 2 full droppers) of the lactose solution and transfer the lactose to the plastic cup. 3. Use a test strip to test the solution by placing the tip with the square into the solution for a few second. Remove strip and allow it to dry for 5 minutes 4. Meanwhile, add 3 ml (~ 1 full dropper) of lactase to the cup with lactose, cover and swirl the cup 10 times to mix. 5. Allow the cup with the enzyme to sit for 5 minutes. Then use a new test strip to test this solution. Let the strip dry for at least 5-10 minutes before reading the color. 6. Record the results in the Data Table. 7. Attach the dry test strip to the Group Data Chart in its corresponding location. LAB: Lactase Page 2 of 7

3 Experiment 2 In this experiment, you will test whether the enzyme lactase can digest the sugar sucrose. First, predict what you think will happen Sucrose with no enzyme: Sucrose with enzyme lactase: Again, to test whether your predictions are correct, you will use glucose test strips to test whether glucose has been produced. 1. Label a plastic cup: SUCROSE 2. One group member should gather 10 ml (~2 full droppers) of the sucrose solution and transfer the sucrose to the plastic cup. 3. Use a test strip to test the solution by placing the tip with the square into the solution for a few second. Remove strip and allow it to dry for 5 minutes. 4. Meanwhile, add 3 ml (~1 full dropper) of lactase to the cup with sucrose, cover and swirl 10 times to mix. 5. Allow the cup with the enzyme to sit for 5 minutes. Then use a new test strip to test this solution. Let the strip dry for at least 5 minutes before reading the color. 6. Record the results in the Data Table. 7. Attach the dry test strip to the Group Data Chart in its corresponding location. Experiment 3 In this experiment, you will determine if the enzyme lactase is required to digest milk. First, predict what you think will happen. Milk with no enzyme: Milk with enzyme lactase: Again, to test whether your predictions are correct, you will use glucose test strips to test whether glucose has been produced. 1. Label a plastic cup: MILK 2. One group member should gather 10 ml (~2 full droppers) of the milk and transfer the milk to the plastic cup. 3. Use a test strip to test the solution by placing the tip with the square into the milk for a few seconds. Remove strip and allow it to dry for 5 minutes. 4. Meanwhile, add 3 ml (~1 full dropper) of lactase to the cup with milk, cover and swirl 8the cup 10 times to mix. 5. Allow the cup with the enzyme to sit for 5 minutes. Then use a new test strip to test this solution. Let the strip dry for at least 5 minutes before reading the color. LAB: Lactase Page 3 of 7

4 6. Record the results in the Data Table. 7. Attach the dry test strip to the Group Data Chart in its corresponding location. Experiment 4 All science experiments must have a proper control. A control is a particular sample that is treated the same as all the rest of the samples except that it is not exposed to manipulated variables. In our case, we must test the lactase enzyme itself to make sure that it is not causing the color change and as a positive control, we need to test pure glucose so we know what a glucose test strip will look like when glucose is present. First, predict what you think will happen: Glucose: Lactase: 1. Label a plastic cup: GLUCOSE 2. One group member should gather 10 ml (~2 full droppers) of the glucose solution and transfer the glucose to the plastic cup. 3. Label a plastic cup: LACTASE 4. One group member should gather 10 ml (~2 full droppers) of the lactase solution and transfer the lactase to the plastic cup. 5. Have a group member use test strips to test glucose and lactase. 6. Wait 5 minutes before reading the color changes. 7. Record the results in the Data Table. 8. Attach the dry test strip to the Group Data Chart in its corresponding location. LAB: Lactase Page 4 of 7

5 DATA TABLE: Experimental Results Experiment 1: LACTOSE Lactose with NO enzyme: Lactose with enzyme Lactase: Experiment 2: SUCROSE Sucrose with NO enzyme: Sucrose with enzyme Lactase: Experiment 3: MILK MILK with NO enzyme: MILK with enzyme Lactase: Experiment 4: CONTROL CONTROLSUCR GLUCOSE: LACTASE: LAB: Lactase Page 5 of 7

6 POST-LAB QUESTIONS: Answer using complete sentences. 1. CLAIM: Lactase is said to be specific. a. EVIDENCE: What evidence from the experiment supports the claim above? b. REASONING: Explain how and why lactase specific. (HINT: Think about what it means to be a specific enzyme. Then, think about how an enzyme works.) 2. There are sugars in milk. a. CLAIM: Which sugar does milk contain: glucose, lactose, or sucrose? b. EVIDENCE: What evidence from the experiment supports your claim above? c. REASONING: Explain how the evidence above connects back to your claim. LAB: Lactase Page 6 of 7