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Example Questions
Example Question #1 : Equilibrium And Kinetics
Which of the following is true regarding the Michaelis constant?
It is the enzyme concentration at which the reaction rate is at maximum
It is the substrate concentration at which the reaction rate is at maximum
It is the substrate concentration at which the reaction rate is half of maximum
It is the enzyme concentration at which the reaction rate is half of maximum
It is the substrate concentration at which the reaction rate is half of maximum
Michaelis constant, or , is defined as the concentration of substrate at which the reaction rate is half the maximum (
). It is a useful measure of how much substrate is needed for reaction to proceed rapidly. A reaction with a high Michaelis constant will need lots of substrate to reach high reaction rates whereas a reaction with low Michaelis constant will need small amounts of substrate to reach high reaction rates.
Example Question #1 : Michaelis Menton Analysis
Which of the following will have the greatest increase in reaction rate?
Increasing the maximum velocity by a factor of 2
Increasing the substrate concentration by a factor of 2
Increasing the Michaelis constant by a factor of 2
Decreasing the substrate concentration by a factor of 2
Increasing the maximum velocity by a factor of 2
Reaction rate, according to Michaelis-Menten model is as follows.
where is reaction rate,
is maximum reaction rate,
is substrate concentration, and
is the Michaelis constant. If we analyze the given options, we will observe that the greatest increase in
occurs when
is doubled (increased by a factor of 2). Increasing substrate concentration by a factor of 2 will have nearly the same effect; however, since
is also found in the denominator it will only slightly contribute to an increase in
.
Note that the units for is molarity,
is molarity, and
is
. Solving for
will give us units of
.
Example Question #1 : Equilibrium And Kinetics
Consider the following reaction parameters.
Substrate concentration =
Michaelis constant =
What can you conclude about the reaction rate?
The reaction rate is
The reaction rate is
The reaction rate cannot be determined from the given information
The reaction rate is
The reaction rate is
To solve this problem we need to use the Michaelis-Menten equation.
where is reaction rate,
is maximum reaction rate,
is substrate concentration, and
is the Michaelis constant. If we plug in the given values we get a reaction rate of
Note that the Michaelis-Menten equation implies that the will never exceed
. Regardless of how high the substrate concentration is, the reaction rate will approach
but will never equal or exceed it. You can try this by substituting very high values for substrate concentration. The
will get very close to 0.2 (
) but will never equal or exceed it.
Example Question #2 : Equilibrium And Kinetics
The Michaelis-Menten model implies that __________ the Michaelis constant will __________ the reaction rate.
decreasing . . . not change
decreasing . . . decrease
increasing . . . not change
increasing . . . decrease
increasing . . . decrease
The Michaelis-Menten equation is as follows.
Where is reaction rate,
is maximum reaction rate,
is substrate concentration, and
is the Michaelis constant. Since the Michaelis constant,
, is in the denominator, the reaction rate is inversely proportional to the Michaelis constant; therefore, increasing the Michaelis constant will decrease the reaction rate.
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