An Enzyme- Substrate Model
Anne McDonald and Michael O'Hare
1991 Woodrow Wilson Biology Institute
- To study reaction rates of an enzyme-mediated reaction.
- To study the effects of environmental variables on enzyme function.
- To collect, graph, and analyze data relating to the reaction.
How often do you find your students not understanding the molecular nature of a chemical reaction? If you are like most science teachers, this is not an uncommon situation. Making the reaction more concrete by using objects that can be readily seen and handled offers a possible solution.
This exercise is designed to enhance the understanding of enzyme-substrate interactions. The activity should take only a short period of time and ideally be used in conjunction with the actual biochemical experiment. The cost is minimal and will provide an engaging activity that students will enjoy.
Suggestions: This activity may best be done outdoors, in the hallway, or gym. Also, it is important not to allow students to return pennies to the original pile between trials.
For a group of 30 students: 500 pennies, one stopwatch, masking tape, 10 tennis balls
TRIAL I - BASELINE
Students should organize into groups of three individuals. The teacher will distribute 500 pennies onto the floor or ground. One member of each team will attempt to pick up as many pennies as possible turning each one so that the head side is facing up. This process will be done six times for a period of 10 seconds each time. The teacher will be responsible for the six timing periods. Do not return pennies to the original pile between timing intervals. Additonal time periods may be needed until all pennies are picked up. Other team members will count and record the number of pennies recovered in each trial period. Place this data into Table I - Team Data.
TRIAL II - DENATURATION
After the pennies have been redistributed on the floor, a different member of your group will have the task of picking up pennies and turning them to the head side up. In this trial the hand used to select the pennies will be taped around all four fingers to represent the partial denaturation of the enzyme. Enzymes, like all proteins, tend to change shape at high temperatures, when in contact with strong acids or bases, or when exposed to heavy metal ions. How well do you expect to do in picking up pennies compared to Trial I? Let's see. Record data into Table I - Team Data.
TRIAL III - ROLE OF COENZYME
After the pennies have been returned to the floor, the third team member will perform the penny selecting task. However, this time he/she will have the help of a teammate, representing the role of a coenzyme. The student picking up pennies merely has to pick them up and give them to his/her partner and they will be responsible for turning them head side up. This last process by the helper may extend beyond the 10 second interval. As before, six time periods will be used and data recorded into Table I- Team Data.
TRIAL 1V - COMPETITIVE INHIBITORS
In this last trial any one member of the team who wishes will retrieve pennies as before but will be handicapped by the taping of a tennis ball or some other object to the palm of the hand to be used. Obviously, this object may interfere with your ability to pick up the pennies. The ball or object represents an inhibitor which is competing with the place on your hand where you pick up the pennies. Try it for six time periods and see what happens. Good luck! Teammates, please record the data in Table I-Team Data.
TABLE I - TEAM DATA
|Time Periods||Trial I|
|0-10 || || || |
|10-20 || || || |
|20-30 || || || |
|30-40 || || || |
|40-50 || || || |
|50-60 || || || |
|60-70 || || || |
|70-80 || || || |
Return to the classroom and compile group data for each trial. Record the totals for each trial at each time interval in Table II-Class Data. In order to calculate the total number of pennies selected at any time period, use the following equation: Total # selected = the sum of all previously # selected.
TABLE II - CLASS DATA
|Time Per||Trial I|
|Sec ||#Sel||Tot #||#Sel||Tot #||#Sel||Tot #||#Sel||Tot #|
|1-10 || |
|10-20 || |
|20-30 || |
|30-40 || |
|40-50 || |
|50-60 || |
|60-70 || |
# Sel = total number picked up by the entire class
Total # = total number picked up at the end of that time interval
Prepare a graph of Table II - Class Data by plotting total #'s of each trial vs.final time of each time period. This will result in a linear graph with four lines illustrating the results of the four sets of trial data.
To avoid error, plot and draw graph line for each trial separately.
- In this activity, what was the enzyme represented by? the substrate? the coenzyme? the inhibitor?
- In trial I, why did the rate eventually decrease? What could have been added to maintain the initial rate?
- If more substrate(pennies) were present in Trial I at the beginning, would the initial rate have been higher? Why or why not?
- If we assume that the enzyme is represented by the hand, what happened to the active site during Trial II?
- Why does an enzyme not work as well if it's active site is changed?
- What environmental factors affect enzyme shape?
- What effect did inhibition have upon the reaction rate?
- How might chemicals affect you if they acted like the tennis ball (inhibitor) during your bodily reactions?