Materials

• Lactase tablet
• 15 mL skim milk
• Water
• Sucrose
• 100-mL graduated cylinder
• 10-mL graduated cylinder
• 3 400-mL beakers
• 5 test tubes
• Test tube rack
• Marking pencil
• Timer
• Hot plate plus pyrex text tube
• Glucose test strips
• Stirring rod

Procedures

• Make Enzyme Solution: Crush a single lactase tablet using mortar and pestle. Add to 200 mL of water. Use stirring rod to stir until dissolved.
• Collect Skim Milk (this solution contains the lactose)
• Make Sucrose Solution: Add 5 grams of sugar to 100 mL of water. Use stirring rod to stir until dissolved.
• Make Denatured Enzyme Solution:

1. Place 20 mL of enzyme solution into a pyrex test tube.
2. Add 200 mL of water to a 400-mL pyrex beaker.
3. Gently position the test tube inside of the beaker.
4. Place the beaker holding the test tube on the hot plate.
5. Boil the water in the beaker for 30 minutes on hot plate.
6. Once boiled, let the solution cool to room temperature.

• Put the appropriate amount of each solution into test tubes before performing tests.

Test Subjects

Wait 2 minutes before testing the solutions in the test tubes. Then, use glucose test strip to determine whether there is glucose present or not. Positive results turn the test strip green.

Results

Analysis and Conclusions

The results of the experiment demonstrate that glucose was present only in the skim-milk and enzyme-solution mixture. This makes sense because this solution contained the lactase tablet, which is the enzyme that catalyzes the reaction forming galactose and glucose. The mixture of skim milk and denatured enzyme solution, however, failed to produce glucose. This shows that when the enzyme was boiled, it was damaged, or denatured. When an enzyme is denatured, it becomes misshapen and thus loses its ability to function — denatured enzymes are ineffective. And the solution containing only skim milk and water, of course, lacked the vital component, lactase, that reacts to form glucose as a product. So, the results make it clear that the lactase enzyme is a necessary catalyst for the hydrolysis of lactose.

As the picture in the title page illustrates, the substrate in this case is lactose, and the enzyme is lactase. The active site of the enzyme is the concave side of lactase (where the substrate binds). The enzyme-substrate complex is pictured in the second phase, when lactose joins to the active site of lactase. The products are glucose and galactose, pictured in the third phase.

Also depicted by the illustration is the fact that the lactase enzyme only reacts effectively with lactose, and not sucrose. Despite having the same chemical formula as lactose, sucrose does not have the particular shape lactose does which allows it to bind to the active site of lactase. This experiment with sucrose demonstrates that the decisive factor in enzymatic reactions is shape, because shape determines whether or not the enzyme-substrate complex will form and subsequently incite a reaction.

Two factors that have the capacity to damage an enzyme are pH and temperature. In this case, however, lowering the pH of the enzyme solution will not affect the enzyme because lactase is accustomed to functioning in the stomach — a very acidic, or low-pH, environment. So lowering the pH will have little effect on the lactase, which already operates in such an environment.

To sum up, lactase is an enzyme that speeds up the hydrolysis process. It catalyzes the hydrolysis of lactose into the monosaccharides galactose and glucose. Because glucose is a product of lactose hydrolysis, testing the presence of glucose in each solution allowed us to determine the extent of the reaction. We found that the mixture composed of milk (which contains lactose) and enzyme solution (which contains lactase) yielded measurable amounts of glucose, a product of the hydrolysis reaction.