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Example Questions
Example Question #1 : Competitive Inhibition
A biochemist finds a bottle labeled "competitive inhibitor of trypsin" in his refrigerator. He finds that the of this enzyme for trypsin is
.
If the biochemist uses of this inhibitor in a solution of trypsin, what is the apparent
of this enzyme?
A competitive inhibitor has no effect on the of an enzyme.
Example Question #2 : Competitive Inhibition
What happens to the of an enzyme-catalyzed reaction when a competitive inhibitor of the enzyme is added?
does not change
increases by a factor of 10
increases by a factor of two
decreases
Cannot be determined
does not change
To answer this question, we need to understand what competitive inhibition is. When a competitive inhibitor is present, an enzyme's active site will be able to bind either substrate or the inhibitor. Thus, for a given substrate concentration, the reaction will be slower in the presence of the inhibitor because sometimes the inhibitor will interfere with the binding of the substrate to the enzyme's active site. However, we're not looking for reaction rate at a given substrate concentration. Instead, we are looking at the maximum possible reaction rate given any amount of substrate concentration. If we keep adding more and more substrate in the presence of the inhibitor, eventually we will get to a point where there is so much substrate present that having the inhibitor around doesn't make a difference on the reaction rate. Therefore, the addition of a competitive inhibitor has no effect on the of an enzyme catalyzed reaction.
Example Question #3 : Competitive Inhibition
What happens to and/or
if a competitive inhibitor is added to an enzyme?
increases
stays the same
decreases
remains the same
remains the same
Competitive inhibitors bind the active site of enzymes, and compete with the substrate for this binding site. Thus, the does not change since if enough substrate is added, regardless of the differential affinities between the substrate and inhibitor for the active site, the substrate will outcompete the inhibitor. However,
increases upon the addition of a competitive inhibitor.
Example Question #1 : Types Of Inhibition
A researcher adds of competitive inhibitors to an existing solution of substrate and enzyme. The researcher notices that the effect of the enzyme decreases. What can the researcher do to increase the effect of the enzyme back to normal levels (to levels before inhibitors were added)?
Increase the volume of the solution
Decrease the volume of the solution
Nothing can be done to bring enzyme activity to normal levels
Increase the concentration of substrate
Increase the concentration of substrate
Competitive inhibitors bind to the active site of the enzyme and prevent substrates from binding to enzyme. This prevents the enzyme-substrate reaction from happening, thereby decreasing the activity of enzymes; however, competitive inhibitors can be overcome by increasing the concentration of substrates. Increase in the amount of substrates will displace the inhibitors from the active site and allow for substrates to bind. This will bring the efficacy of the enzyme back up to normal levels.
Increasing and decreasing the volume of the solution will concentrate or dilute all species in the solution, respectively. This will not decrease the effects of competitive inhibitors on the enzyme.
Example Question #5 : Competitive Inhibition
Competitive inhibitors bind to __________ on enzyme and form __________ bonds.
allosteric site . . . strong
allosteric site . . . weak
active site . . . strong
active site . . . weak
active site . . . weak
There are two types of sites on the enzyme where molecules can bind. Active sites are the main location for substrate-enzyme binding. These sites usually involve weak, reversible bonds (such as hydrogen bonds) between substrate and enzyme. Allosteric site, on the other hand, are found at a different location on the enzyme and bind certain types of inhibitors and modulators of the enzyme. These are usually more permanent bonds (covalent bonds) and are irreversible.
Competitive inhibitors bind to active sites and form weak, reversible bonds. This is why we can dissociate competitive inhibitors from the active site by increasing the concentration of substrates. Substrates will compete for the active site and displace bound competitive inhibitors.
Example Question #6 : Competitive Inhibition
Which of the following is true regarding competitive inhibition?
It decreases the attraction between enzyme and substrate only
It decreases the maximum effect of the enzyme only
It decreases the maximum effect of the enzyme and it decreases the attraction between enzyme and substrate
None of these
It decreases the attraction between enzyme and substrate only
Competitive inhibition is characterized by an increase in the Michaelis-Menten constant, . Note that this constant represents the substrate concentration at which half the enzymes are occupied with substrate. If
increases, then it suggests that a higher concentration of substrate is needed to occupy half the enzymes.
is also a measure of the affinity between substrate and enzyme. As
increases, the affinity decreases and more substrate is required to bind 50% of the enzyme. Competitive inhibitors bind to the active site of the enzyme and compete with the substrate for the binding site on the enzyme, thereby decreasing the affinity and increasing
.
Competitive inhibitors do not alter the maximum velocity of an enzyme-substrate reaction. Recall that enzymes speed up reactions; therefore, the velocity of a reaction is a direct measure of its efficacy. This means that competitive inhibitors do not alter the efficacy of the enzyme.
Example Question #7 : Competitive Inhibition
Which of the following best describes the function of competitive inhibitors?
Increase the
Increase the
Increase the
No change in
Decrease the
Increase in
No change in
Increase the
No Change in
Decrease the
Increase the
No change in
Competitive inhibitors bind to the substrate binding site of an enzyme and have the following effect: Increase , No change in
.
Noncompetitive inhibitors bind to a site other than the substrate binding site and have the following effect: No change in , Decrease in
.
Increasing the , lowers the affinity since the
is the substrate concentration at which the reaction proceeds as one-half of
.
Example Question #1 : Competitive Inhibition
Carbon monoxide binds to hemoglobin at the same site as oxygen, and it does so with a much higher affinity - carboxyhemoglobin results. The type of inhibition by carbon monoxide on hemoglobin is which of the following?
Mixed-inhibition
Competitive inhibition
Uncompetitive inhibition
No inhibition
Noncompetitive inhibition
Competitive inhibition
Because carbon monoxide binds at the same site as oxygen, this is a form of competitive inhibition. In order to overcome this type of inhibition, the concentration of substrate (oxygen) needs to be increased.
Example Question #1 : Enzyme Kinetics And Inhibition
Carbon monoxide binds to hemoglobin at the same site as oxygen, and with a much higher affinity - carboxyhemoglobin results. What is true about the type of inhibition occurring here?
is raised for this type of inhibition
is lowered for this type of inhibition
remains unchanged for this type of inhibition
This type of inhibition can be overcome by increasing the amount of substrate available
This type of inhibition can be overcome by decreasing the amount of substate available
This type of inhibition can be overcome by increasing the amount of substrate available
The type of inhibition being described here is competitive. The carbon monoxide binds to the same site that oxygen does. Therefore, by increasing the amount of substrate available, the inhibitor can be outcompeted. This is why Vmax for competitive inhibition is unchanged. Km on the other hand, is decreased for competitive inhibition.
Example Question #2 : Enzyme Kinetics And Inhibition
Which of the following molecules is most likely to competitively inhibit an enzyme that catalyzes the reaction of ?
Glucose
A molecule can only competitively inhibit another molecule if it fits into the same active site in the enzyme. In the reaction, goes into the active site of the enzyme, and so only a molecule with its similar structure can competitively inhibit it -
.
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