An Introduction to Enzyme Kinetics

Background: Enzymes work to speed up biological reactions by lowering their activation energy. There are certain conditions that must be met for an enzyme to work efficiently: substrate concentration, temperature, and pH.

Task: Your objective is to observe the effects of different substrate and enzyme concentrations on toothpickase and to determine the rate of enzyme activity of toothpickase. The toothpicks will represent the substrate and your thumb and index finger represent the active site of the enzyme toothpickase. To catalyze the reaction (breaking the toothpick completely in half) you may only use one hand. Toothpicks not broken completely in half do not count as products.

Materials:150 toothpicksstopwatchpaper plate

icetape

Roles: In small groups assign the following roles:

~ Toothpickase (person who will break toothpicks)

~ Timer (will tell toothpickase when to start and stop)

~ Counter (will count number of toothpicks)

~ Recorder (will record in data tables)

Procedure:

Part A:

  1. Place 50 toothpicks on the small paper plate in front of toothpickase.
  2. Using only ONE hand, toothpickase will then begin breaking toothpicks in half.
  3. The recorder will keep track of the number broken and make sure that broken toothpicks remain in the pile (as products and reactants mix during chemical reactions).
  4. Toothpickase will have 10 seconds for its first enzymatic activity. The timer will tell toothpickase when to start and stop, using a stopwatch to keep time.
  5. At the end of the 10 seconds record the number broken on the data table.
  6. Repeat steps 2-5, this time giving toothpickase 20 seconds to break the toothpicks. Do not separate the broken toothpicks from the whole toothpicks. Record.
  7. Repeat steps 2-5, but for 30 seconds. Record.
  8. Repeat steps 2-5, but for 60 seconds. Record. (If you run out of toothpicks before you run out of time, record the amount of time it took to do so).

Part B

  1. Get 50 unbroken toothpicks.
  2. Spread out the toothpicks so that toothpickase has to reach for them (toothpick concentration decreases.
  3. Repeat steps 2-8 from Part A.
  4. Record your results.

Part C

  1. Place 50 unbroken toothpicks on the small paper plate in front of toothpickase.
  2. Repeat steps 2-8 from Part A, but now either alter the pH (by taping your index finger to your thumb) or change the temperature (by putting your hand in ice for 1 minute before each trial).
  3. Record your results.

Toothpickase Data Collection

Hypothesis Part A: What will happen to the enzyme activity as substrate (unbroken toothpicks) diminished? ______

Hypothesis Part B: What will happen to the enzyme activity with the toothpicks spread out (decrease in substrate concentration)? ______

Hypothesis Part C: What will happen to the enzyme activity with a pH or temperature change? ______

IV: ______

DV: ______

Part A - Toothpickase Activity

Interval Time (sec) / Cumulative time (sec) / Toothpicks Broken / Total Broken (Cumulative)
10 / 10
20 / 30
30 / 60
60 / 120 /
Time (sec) / Rate (Toothpicks/Time)
0-10
0-120

Part B - Toothpickase Activity with decreased concentration

Interval Time (sec) / Cumulative time (sec) / Toothpicks Broken / Total Broken (Cumulative)
10 / 10
20 / 30
30 / 60
0 / 120
Time (sec) / Rate (Toothpicks/Time)
0-10
0-120

Part C – Toothpickase Activity with pH (taped) or temperature change

Time (sec) / Rate (Toothpicks/Time)
0-10
0-120
Interval Time (sec) / Cumulative time (sec) / Toothpicks Broken / Total Broken (Cumulative)
10 / 10
20 / 30
30 / 60
60 / 120

Toothpickase Analysis and Conclusion

Create a graph to show total broken toothpicks (cumulative) over time. You will need to include: a title, labels for the x and y axis, correct units and a key.

______

Conclusion Questions:

1. What happened to the reaction rate as the supply of unbroken toothpicks (substrate) diminished? Why did this happen?

2. What happened to the reaction rate when the toothpicks were all spread out? Why did this happen?

3. What happened to the reaction rate when the temperature or pH was altered? Why did this happen?

4. What do you think would happen to the reaction rate if the enzyme could separate the products and reactants?Why?