Understanding Lactase Enzyme Reaction: Temperature and pH Effects

Enzyme

1. Define the following and explain how each relates to the lactase chemical reaction . Be sure to read the information located in the Home, Background and Explore Model tabs to the left of the simulate tab.

a.Enzyme

b.Substrate

c.Active site

d.Rate of reaction

e.Activation Energy

Simulation Option 1: Temperature 

1. Start with the initial lactose at 500 mg/dL and the pH at 7. Do not vary these parameters while testing for temperature, they are environmental controls. The temperature is in degreesCelsius.  

2. Vary the temperature by 20oC (you can slide the cursor over to the right or type the number directly in the box). 

3. Run each experiment 3 times (for reliability in the results.) and record the rate or reaction in the table below. The rate of reaction should be in mg/dL of glucose per minute. Place the arrow on the line in the graph and a  “+” symbol appears Click on the line at the end of the 20 minutes and the concentrations will be displayed at the bottom of the graph under the “X” axis (minutes).

Questions for Simulation 1

A. What are the results of the simulation? What is the optimal temperature? 

B. Explain why your results of the optimal temperature of the lactase enzyme make sense for the human enzyme? Explain the results in terms of the structure and function of proteins.

Simulation Option 2: pH

1. Start with the initial lactose at 500 mg/dL and the temperature at 25 degrees Celsius.  Do not vary these parameters while testing for pH, they are environmental controls. 

2. Vary by a pH of 3. Run each experiment 3 times (for reliability in the results.) 

3. Record the rate of reaction in the table below. The rate of reaction should be in mg/dL of glucose per minute (see directions in simulation #1)

Questions for Simulation 2

A. What are the results of the simulation? What is the optimal pH? 

B. Explain why your results of the optimal pH of the lactase enzyme make sense for the human enzyme? Explain the results in terms of the structure and function of proteins

Analysis Questions:

1. Write the decomposition chemical reaction for the effect of lactase on lactose.  Indicate the substrate, the enzyme, and the products. 

2.  Each enzyme operates at an ideal pH and temperature, which may vary for other enzyme.

(a) Pepsin is an enzyme found in the human stomach for digesting protein. What  would be the optimum pH conditions for pepsin? What effect does entry into the intestines have on pepsin? 

(b) Some bacteria, called thermophiles, live in the hot springs in our Western National Parks. Explain what possible adaptations allow survival under such environmental conditions

3. Predict how the milk digestion is affected in individuals that lack functional copies of  the gene encoding lactase. Justify your response. Why would having the enzyme lactase as an adult be an evolutionary advantage?

4.  Write a summary statement for the biological principles that you have learned from this laboratory exercise.