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Bio 114: Virtual Enzyme Lab
Enzymes
Enzymes are usually more efficient than man-made catalysts operating under the
same conditions. Because many enzymes with different specificities occur in a
cell, each enzyme must be very efficient. One molecule of the enzyme catalase,
for example, can produce 10*12 molecules of oxygen per second.
Enzymes have a special affinity for the substrate. They fit together, matching in
shape and charge. The part of the enzyme where the substrate fits, is called the
active site. The amino acid residues in the active site are in the right 3D
conformation to bind and modify the substrate. The combination of substrate
molecules with enzymes also involves collisions between the two. The substrate
must reach the active site. As the substrates are used up during a reaction
(converted to products), the chance of their colliding with the enzyme decreases,
this results in a decrease in the amount of product being produced (reaction
rate).
In this week's lab we will measure the rate of a reaction by measuring the amount
of substrate remaining after some period of time. This is a little unusual. In our
reaction, H2O2 is the substrate and H2O2 is converted to H2O + O2 as the
reaction proceeds. Rather than measuring the formation of the product as an
indicator of the reaction, we will measure the disappearance of substrate.
For instance:
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We start with 3 ml of H2O2 from your bathroom cabinet
Added Catalase
Wait three minutes
Measure and find 1 ml of H2O2 remaining
1. How much H2O2 was consumed in the reaction?
2. If we had repeated the experiment, measured and found 2 ml of H2O2
remaining, would this second reaction have a higher or lower rate of reaction?
Higher
Lower
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Why would this be?
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Enzyme Lab –
A quick review: We added enzyme and substrate to four tubes, each at a different
temperature. We let the reaction "run" for 3 minutes, then stopped it with H2SO4. We
measured the remaining substrate by titration with KMnO4. Your titration results are
below. Now let's analyze your results and answer some questions.
These were your results:
Tube 1
Tube 2
Tube 3
Tube 4
Remember what you were measuring in each titration; the amount of substrate
remaining after the reaction was stopped. This is only an indirect measure of the
actual rate of reaction. Please answer the questions below.
Questions::
1. Which tube had the highest rate of reaction?
Tube 1
Tube 2
Tube 3
Tube 4
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2. What variable(s) caused the differences in reaction rates for each tube?
Temperature
H2SO4
Time and Temperature
Substrate Concentration
3. How would you explain the difference between the reaction rate at 34°C and at
the rate at 44°C ?
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Identify the following pieces of information concerning the experiment.
4. Purpose/Objective(s): What is this lab supposed to show/teach someone?
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5. Identify the variables used in this experiment:
Independent: ____________________________________________________
Dependent: _____________________________________________________
6. Identify the controlled variables in the experiment.
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7. Analyze the data that was collected and develop a conclusion using it to
support your statement.
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8. Why is it important to let the test tubes “acclimate” to the temperature of the
water bath before beginning the experiment?
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9. The H2O2 used in the experiment is the (product or reactant). It is the
(substrate or enzyme).
10. What reason might the catalase be cold when collected in the pipette and
used in the experiment?
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11.
11. What does the H2SO4 do to the contents of the test tube?
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12.
12 What reaction has been occurring in the test tube?
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13.
13 What change occurs during the titration to let you know that the titration is
finished?
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14.
14 Why is KMnO4 (potassium permanganate) used in the titration?
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15. How does the volume of KMnO4 (potassium permanganate) relate to H2O2
(hydrogen peroxide)?
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16. Define the following words:
Titration:
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Substrate:
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Product:
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Active site:
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Denaturation:
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