Enzymes:
Graphing, Critical Thinking, and Calculating Reaction Rates
Teacher Answer Key
1. What do enzymes do?
Enzymes lower the activation energy of a chemical reaction. This makes the reaction take place
faster and at a lower temperature.
2. What kind of compounds are enzymes?
Enzymes are proteins.
3. What is activation energy?
Activation energy is the amount of energy that reactant molecules must absorb to make them
unstable enough so that the bonds holding the atoms of the reactants together are broken.
4. What is a substrate?
Substrate molecules are reactant molecules that are being converted to new and different products.
5. What is an active site?
The active site is a pocket or groove on the surface of the enzyme into which the substrate
molecules must fit.
Exercise 1: Graphing and Analyzing an Enzymatic Reaction.
Amount of Product Formed vs. Time
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, 6. Notice on the graph that the time period between 0 and 3 minutes forms a straight line on the
graph. What does this indicate about the rate of reaction?
The reaction is proceeding at a constant rate. (The slope is constant.) The rate of reaction is not
increasing. (Calculations of the reaction rates, below, will confirm that the reaction rate is constant
during this time period.) At the beginning of the reaction, there is so much substrate available to
react that the enzymes are saturated and are working as fast as they can. The reaction rate (as
indicated by the steep slope) is highest from 0-3 min.
7. Calculate the initial rate of the reaction (between 0 and 1 min):
Rate = 0 μmoles − 10 μmoles
0 min − 1 min
Rate = − 10 μmoles
− 1 min
Rate = 10 μmoles/min
8. Calculate the rate of reaction between 2 and 3 minutes:
Rate = 20 μmoles − 30 μmoles
2 min − 3 min
Rate = − 10 μmoles
− 1 min
Rate = 10 μmoles/min
9. How does the reaction rate between 0 and 1 minute compare to the reaction rate between 2 and 3
minutes?
The reaction rates are the same. The reaction is proceeding at the same rate between 0 and 1
minute as it is between 2 and 3 minutes.
At the beginning of the reaction, there is an abundance of substrate available for the reaction. The
enzymes are working as fast as they can (at a constant rate) to convert these substrates into
products.
10. Does your answer in question 9 agree with your answer in question 6?
Although answers may vary (may be yes or may be no) the answers for #9 and #6 SHOULD agree. It
is important that you understand why this is true.
11. In a graph of an enzymatic reaction, explain why the line begins as a straight line.
At the beginning of an enzymatic reaction, there is an abundance of substrate available for the
reaction. The enzymes are working as fast as they can and at a constant rate high rate (as shown
by the slope) to convert these substrates into products. Product formation is occurring at a
constant rate.
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Graphing, Critical Thinking, and Calculating Reaction Rates
Teacher Answer Key
1. What do enzymes do?
Enzymes lower the activation energy of a chemical reaction. This makes the reaction take place
faster and at a lower temperature.
2. What kind of compounds are enzymes?
Enzymes are proteins.
3. What is activation energy?
Activation energy is the amount of energy that reactant molecules must absorb to make them
unstable enough so that the bonds holding the atoms of the reactants together are broken.
4. What is a substrate?
Substrate molecules are reactant molecules that are being converted to new and different products.
5. What is an active site?
The active site is a pocket or groove on the surface of the enzyme into which the substrate
molecules must fit.
Exercise 1: Graphing and Analyzing an Enzymatic Reaction.
Amount of Product Formed vs. Time
1
, 6. Notice on the graph that the time period between 0 and 3 minutes forms a straight line on the
graph. What does this indicate about the rate of reaction?
The reaction is proceeding at a constant rate. (The slope is constant.) The rate of reaction is not
increasing. (Calculations of the reaction rates, below, will confirm that the reaction rate is constant
during this time period.) At the beginning of the reaction, there is so much substrate available to
react that the enzymes are saturated and are working as fast as they can. The reaction rate (as
indicated by the steep slope) is highest from 0-3 min.
7. Calculate the initial rate of the reaction (between 0 and 1 min):
Rate = 0 μmoles − 10 μmoles
0 min − 1 min
Rate = − 10 μmoles
− 1 min
Rate = 10 μmoles/min
8. Calculate the rate of reaction between 2 and 3 minutes:
Rate = 20 μmoles − 30 μmoles
2 min − 3 min
Rate = − 10 μmoles
− 1 min
Rate = 10 μmoles/min
9. How does the reaction rate between 0 and 1 minute compare to the reaction rate between 2 and 3
minutes?
The reaction rates are the same. The reaction is proceeding at the same rate between 0 and 1
minute as it is between 2 and 3 minutes.
At the beginning of the reaction, there is an abundance of substrate available for the reaction. The
enzymes are working as fast as they can (at a constant rate) to convert these substrates into
products.
10. Does your answer in question 9 agree with your answer in question 6?
Although answers may vary (may be yes or may be no) the answers for #9 and #6 SHOULD agree. It
is important that you understand why this is true.
11. In a graph of an enzymatic reaction, explain why the line begins as a straight line.
At the beginning of an enzymatic reaction, there is an abundance of substrate available for the
reaction. The enzymes are working as fast as they can and at a constant rate high rate (as shown
by the slope) to convert these substrates into products. Product formation is occurring at a
constant rate.
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