Safety Precautions:

Use caution when handling glass test tubes, stirring rods, and beakers. Wear goggles at all times. Be careful around the hot plate and when using hot water/hot enzyme solutions and their containers.

Purpose:

From the lab introduction handout: “The purpose of this lab is to explore the properties of the enzyme lactase. By the end of this lab, you should understand the biological function of enzymes and why they are important in the body. You will also examine the specificity of an enzyme to a specific substrate.”

Introduction:

The enzyme we are working with in this lab is lactase. Lactase, like other enzymes, is a protein molecule that acts as a biological catalyst, in a similar way to chemical catalysts because they both increase the rate of reactions but are not used up in the reaction. However, enzymes perform more specific reactions than chemical catalysts. Lactase helps humans digest the substrate lactose- composed of the two monosaccharides galactose and glucose- which is in dairy products, such as the skim milk used in this lab. Lactase catalyzes the hydrolysis of lactose, breaking it down into the monosaccharides glucose and galactose. Lactose intolerance occurs when the body does not produce the amount of lactase needed to hydrolyze the lactose, making the digestion of dairy products difficult. Industries make “lactose-free” milk by adding the lactase enzyme to milk, hydrolyzing the lactose before consumption. In this experiment, we will know how much lactose reacted by measuring the presence and amount of glucose. If glucose is present in a solution, we will know that the lactose has been broken down, and the glucose test strip will turn from yellow to blue-green.

Procedure:

Lab Conclusion Questions

1.)Diagram of the Lactose/Lactase reaction:

2.)“Sucrose and Lactose have the same chemical formula (C12H24O11). Why did the enzyme react to lactose but not to sucrose?”

In order for an enzyme to react with a substrate the substrate needs to be the same shape as the active site of the enzyme. The shape of sucrose is not the same shape as that of lactose which causes sucrose to not react with the enzyme because sucrase does not have an active site which will fit and react with lactose.

3.)“What happened when the enzyme was boiled?”

When the enzyme was boiled, its shape was disrupted which denatured the enzyme, causing it to no longer function properly.

4.) “Another way to affect an 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?”

Eventually the enzyme will denature if the pH is lowered because all enzymes have an optimal pH level that they function the best at. If the pH is lowered to an extreme than the enzyme will stop functioning properly and efficiently.

5.) Lactase is speeding up what type of chemical reaction-dehydration or hydrolysis?

The chemical reaction is a hydrolysis reaction. It is a hydrolysis reaction because lactase catalyzes the reaction of lactose into glucose and galactose and a water molecule is added to the products.

Thank you!