Lactose and Lactase: Exploring Enzymes as Catalysts

Problem:

Does more lactase create more glucose when mixed with the lactose in milk?

Materials

• Milk (it can be fat free, 2%, skim, or whole)
• 6 or more small, clean glasses
• 6 or more clean spoons
• ½ cup measuring spoon or measuring cup
• 6 or more dairy digestive aid tablets, which contain fast-acting lactase
• Spatula
• Glucose test strips (available at some drug stores in the diabetes section, or online)
• Teaspoon
• Baking soda
• White vinegar

Procedure 1

How does the amount of enzyme effect the digestion of milk sugar?

1. Go online with an adult to conduct some research about enzymes. What can you find out about how enzymes work? Make a hypothesis as to how much glucose will be produced in glasses of milk mixed with 0, 1, or 2 lactase tablets. Make sure to explain your reasoning!
2. Measure a half cup of milk into three glasses. Place a spoon inside each.
3. Use the spatula handle to crush three of the lactase tablets while they’re still encased in their foil packaging. Why do you think it’s important to crush up the tablets?
4. Open the foil and pour the crushed contents of one tablet in your second glass.
5. Place the contents of two more crushed tablets in your third glass.
6. Stir each glass once a minute for ten minutes. Enzymes need time to work.
7. Use your glucose test strips according to the directions on the packaging to find the amounts of glucose present in each of the three glasses of milk. Make sure you record your results. Do your results confirm your hypothesis?

Procedure 2:

Can other chemicals affect how well a digestive enzyme works?

1. Make another hypothesis about how you think adding baking soda or vinegar might affect glucose production. Do some research first: What other chemicals are normally present in the human digestive system? How can we describe those chemicals?
2. Fill each of three glasses with ½ cup milk. Place a spoon inside each.
3. Add 1 teaspoon baking soda to the first glass. Stir.
4. Add 1 teaspoon vinegar to the second glass. Stir.
5. Don’t add any vinegar or baking soda to your third glass.
6. Use the spatula handle to crush three lactase tablets while they’re still encased in their foil packaging.
7. Peel back the foil packaging of one crushed pill and pour the contents into your first glass. Stir the contents of the glass.
8. Peel back the foil packing of another crushed pill and pour the contents into your second glass. Stir the contents of the glass.
9. Peel back the foil packing of your third crushed pill and pour the contents into your third glass. Stir the contents of the glass.
10. Stir each glass once a minute for ten minutes.
11. Use your glucose test strips according to the directions on the packaging to find the amounts of glucose present in each of your two glasses of milk. Make sure you record your results.
12. Do your results confirm your hypothesis?

Results

In the first experiment, you shouldn’t have found any glucose in the plain glass of milk, and you should have found the same amount of glucose in each of the two glasses of milk mixed with lactase. In the second experiment, the glass of milk with baking soda and lactase probably produced less glucose than the glass that had only lactase added to it. The glass of milk with added vinegar should have produced slightly more glucose than the glass that had only lactase added to it.

Why

Normal milk doesn’t have any glucose—just lactose. This is why you didn’t find any when you tested the glass. You should have found glucose in the other two cups, but why wasn’t there more in the cup that had more lactase added to it? Remember, lactase is an enzyme, and we describe enzymes as catalysts: a substance that helps chemical reactions happen without being used up. Each bit of enzyme can break down multiple molecules of milk sugar, so as long as you stir the glass and wait long enough, even a tiny bit of the enzyme is enough to break down all the lactose in the milk!

Now let’s figure out how we can explain the results of our second experiment. Lactase goes to work in your stomach and small intestine, where there is also lots of acid. The lactase enzyme is not affected by the acidy vinegar which might even help the lactase do its job better. Baking soda, on the other hand, is a base, and we don’t find a lot of basic substances in our digestive systems! Basic compounds like baking soda can damage enzymes like lactase, preventing them from working as well.

What other variables can you investigate? Try to see how heat and cold, and other chemicals affect how well lactase works!