Enzyme Kinetics and Inhibition - Biochemistry
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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 biochemist finds a bottle labeled "competitive inhibitor of trypsin" in his refrigerator. He finds that the
If the biochemist uses
A competitive inhibitor has no effect on the 
of an enzyme.
A competitive inhibitor has no effect on the
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What happens to the 
of an enzyme-catalyzed reaction when a competitive inhibitor of the enzyme is added?
What happens to the
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.
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
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What happens to 
and/or 
if a competitive inhibitor is added to an enzyme?
What happens to
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.
Competitive inhibitors bind the active site of enzymes, and compete with the substrate for this binding site. Thus, the
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Which of the following is true regarding competitive inhibition?
Which of the following is true regarding competitive inhibition?
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.
Competitive inhibition is characterized by an increase in the Michaelis-Menten constant,
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.
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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)?
A researcher adds
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.
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.
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Competitive inhibitors bind to on enzyme and form bonds.
Competitive inhibitors bind to on enzyme and form bonds.
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.
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.
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Which of the following best describes the function of competitive inhibitors?
Which of the following best describes the function of competitive inhibitors?
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 
.
Competitive inhibitors bind to the substrate binding site of an enzyme and have the following effect: Increase
Noncompetitive inhibitors bind to a site other than the substrate binding site and have the following effect: No change in
Increasing the
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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?
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?
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.
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.
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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?
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?
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.
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.
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Which of the following molecules is most likely to competitively inhibit an enzyme that catalyzes the reaction of 
?
Which of the following molecules is most likely to competitively inhibit an enzyme that catalyzes the reaction of
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 - 
.
A molecule can only competitively inhibit another molecule if it fits into the same active site in the enzyme. In the reaction,
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Suppose that an enzyme has a critical functional group in its active site that is heavily involved in carrying out the catalytic mechanism. To perform its role in catalyzing its target reaction, this particular functional group must be able to accept a proton from the intermediate during the process. If the pKa of this functional group is equal to 7.0, then what percentage of the total enzyme active sites for this enzyme would be in the active form in a solution in which the pH is equal to 6.4?
Suppose that an enzyme has a critical functional group in its active site that is heavily involved in carrying out the catalytic mechanism. To perform its role in catalyzing its target reaction, this particular functional group must be able to accept a proton from the intermediate during the process. If the pKa of this functional group is equal to 7.0, then what percentage of the total enzyme active sites for this enzyme would be in the active form in a solution in which the pH is equal to 6.4?
In order to solve this problem, we'll need to make use of the Henderson-Hasselbalch equation.
Therefore, for every 0.25mol of base (deprotonated functional group), there is 1mol of acid (protonated functional group). Furthermore, we're told in the question stem that the functional group must be able to accept a proton from the intermediate during the catalytic mechanism. To accept a proton, the functional group would need to be in its deprotonated form to be active. Hence, we're trying to find the percentage of the deprotonated form. To find this value, we'll use the following expression:
In order to solve this problem, we'll need to make use of the Henderson-Hasselbalch equation.
Therefore, for every 0.25mol of base (deprotonated functional group), there is 1mol of acid (protonated functional group). Furthermore, we're told in the question stem that the functional group must be able to accept a proton from the intermediate during the catalytic mechanism. To accept a proton, the functional group would need to be in its deprotonated form to be active. Hence, we're trying to find the percentage of the deprotonated form. To find this value, we'll use the following expression:
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Which of the following does not increase reaction rate?
Which of the following does not increase reaction rate?
Catalysts lower activation energy. Lowering activation energy causes the reaction rate to increase. Removing catalysts will cause the reaction to slow down because the activation energy will be higher. Cofactors assist in the function of enzymes and can increase reaction rate.
Catalysts lower activation energy. Lowering activation energy causes the reaction rate to increase. Removing catalysts will cause the reaction to slow down because the activation energy will be higher. Cofactors assist in the function of enzymes and can increase reaction rate.
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There are at least four types of glucose transporter in the body. GLUT1 and GLUT3 are located in most tissues including the brain and the red blood cells. These glucose transporters rapidly take up glucose from the blood but have the lowest 
value. GLUT2 is commonly found in the liver and the pancreas. GLUT2 has a lower affinity for glucose but has the highest 
value. GLUT4 is common in skeletal tissues and in adipose tissues. This transporter is normally not active for uptake unless stimulated by insulin or during exercise.
What is the mechanism by which the GLUT proteins in the transport glucose into the cell from the blood?
There are at least four types of glucose transporter in the body. GLUT1 and GLUT3 are located in most tissues including the brain and the red blood cells. These glucose transporters rapidly take up glucose from the blood but have the lowest
What is the mechanism by which the GLUT proteins in the transport glucose into the cell from the blood?
Since there will be more glucose surrounding the cell, the GLUT proteins utilize a chemical gradient to transport glucose into the cell.
Since there will be more glucose surrounding the cell, the GLUT proteins utilize a chemical gradient to transport glucose into the cell.
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If the level of ATP suddenly increases in a cell, facilitated diffusion in the cell will .
If the level of ATP suddenly increases in a cell, facilitated diffusion in the cell will .
Facilitated diffusion acts independently of the level of intracellular ATP. Therefore, a change in ATP concentration will not affect the rate of facilitated diffusion.
Facilitated diffusion acts independently of the level of intracellular ATP. Therefore, a change in ATP concentration will not affect the rate of facilitated diffusion.
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If the chloride concentration is 
in the cell and 
in the blood, what is the electrochemical potential of chloride ions across the plasma membrane at 
when the electrical potential across the membrane is 
and the inside is negative?
If the chloride concentration is
Where 
is Faraday's constant 
, 
is the charge of a chloride ion, which is 
, and 
is 
or 
. Be sure to keep units consistent.
Where
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You make a Hill plot reflecting the binding kinetics of a receptor and see that the slope (the Hill coefficient) is 1. What does this indicate about your receptor?
You make a Hill plot reflecting the binding kinetics of a receptor and see that the slope (the Hill coefficient) is 1. What does this indicate about your receptor?
If the Hill coefficient of the Hill plot is equal to 1, then binding is non-cooperative. If the Hill coefficient is greater than 1, binding is positively cooperative; if less than 1, binding is negatively cooperative. The Hill plot does not make any conclusions about the rate of a reaction, which involves Michaelis-Menten kinetics.
If the Hill coefficient of the Hill plot is equal to 1, then binding is non-cooperative. If the Hill coefficient is greater than 1, binding is positively cooperative; if less than 1, binding is negatively cooperative. The Hill plot does not make any conclusions about the rate of a reaction, which involves Michaelis-Menten kinetics.
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Given the following kinetic parameters, which of the following enzymes would show the most efficiency?
Given the following kinetic parameters, which of the following enzymes would show the most efficiency?
To answer this question, we need to understand what enzyme efficiency is and how it's calculated.
Enzyme efficiency refers to how much substrate a given enzyme can convert into product for a given amount of substrate. In other words, an enzyme that is very efficient can convert substrate into product very quickly, even when there is not very much of that substrate around.
To calculate an enzyme's efficiency, we need to take into account these two factors by considering the variables they are associated with.
The 
for a given enzyme represents the "turnover number." This value is a rate constant that is unique to a particular enzyme at a certain temperature (generally under physiological conditions). This rate constant refers to the maximum amount of substrate that an enzyme can convert into product in a given amount of time. Or, put another way, the rate constant gives the maximum reaction rate for a particular enzyme when that enzyme is completely saturated with substrate.
On the other hand, the 
of an enzyme tells us the amount of substrate that needs to be present in order for the reaction rate to be at exactly half of its maximal value. This is almost the same as saying how much attraction a given enzyme has for its substrate. In fact, under certain conditions, we can use the of an enzyme as an accurate measure of the affinity that the enzyme has for its substrate.
Relating these two values back to enzyme efficiency, we can calculate its value by taking the ratio of the two. In other words,
So, the greater the and the lower the , the greater the enzyme's efficiency will be.
From the answer choices shown, we can see that the ratio is greatest for the enzyme that has a of 
and a of 
, which gives an efficiency value of 
.
To answer this question, we need to understand what enzyme efficiency is and how it's calculated.
Enzyme efficiency refers to how much substrate a given enzyme can convert into product for a given amount of substrate. In other words, an enzyme that is very efficient can convert substrate into product very quickly, even when there is not very much of that substrate around.
To calculate an enzyme's efficiency, we need to take into account these two factors by considering the variables they are associated with.
The
On the other hand, the
Relating these two values back to enzyme efficiency, we can calculate its value by taking the ratio of the two. In other words,
So, the greater the
From the answer choices shown, we can see that the ratio is greatest for the enzyme that has a
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Which of the following coenzymes functions primarily by transferring one-carbon groups?
Which of the following coenzymes functions primarily by transferring one-carbon groups?
This question is asking us to identify a coenzyme that functions by transferring one-carbon groups. So let's take a look at each answer choice to determine what it does.
Nicotinamide Adenine Dinucleotide (
) and Flavin Adenine Dinucleotide (
) both function as carriers of high-energy electrons. Both of these coenzymes are heavily involved in taking high-energy electrons from various compounds as they are broken down during catabolic reactions. Once collected, these coenzymes deposit their high-energy electrons into the electron transport chain, allowing for a great deal of ATP to be generated for energy.
Pyridoxal Phosphate (
) is a coenzyme that is primarily involved in transamination reactions. These are reactions that take an amino group from amino acids, and transfer that amino group to an alpha-keto acid, converting it into an amino acid in the process. Thus, this coenzyme transfers amino groups.
Thiamine Pyrophosphate (
) is a coenzyme responsible for transferring two-carbon groups. For instance, 
serves as a coenzyme for the pyruvate dehydrogenase complex, which is responsible for converting pyruvate into acetyl-CoA.
Finally, S-Adenosyl Methionine (
) is a coenzyme mainly responsible for transferring one-carbon groups in their most reduced form, as methyl groups. As the most potent methyl group donor in biological systems, 
functions as a coenzyme for many methyltransferase enzymes.
This question is asking us to identify a coenzyme that functions by transferring one-carbon groups. So let's take a look at each answer choice to determine what it does.
Nicotinamide Adenine Dinucleotide (
Pyridoxal Phosphate (
Thiamine Pyrophosphate (
Finally, S-Adenosyl Methionine (
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An enzyme has been exposed to an inhibitor of unknown type. When testing the efficiency of the enzyme in the presence of the inhibitor, the maximum velocity of the enzyme has been reduced to 60%. However, the amount of substrate needed to achieve half of the maximum velocity of the enzyme has not been affected by the inhibitor.
Based on this information, what is the type of inhibitor?
An enzyme has been exposed to an inhibitor of unknown type. When testing the efficiency of the enzyme in the presence of the inhibitor, the maximum velocity of the enzyme has been reduced to 60%. However, the amount of substrate needed to achieve half of the maximum velocity of the enzyme has not been affected by the inhibitor.
Based on this information, what is the type of inhibitor?
Based on the information, we have seen that 
for the enzyme has been unaffected, but the 
for the enzyme has been lowered. This type of inhibition is observed with noncompetitive inhibitors.
Based on the information, we have seen that
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Which of the following would be observed in the presence of a competitive enzyme inhibitor?
Which of the following would be observed in the presence of a competitive enzyme inhibitor?
Competitive inhibitors bind to the active site of the target enzyme. Km is the substrate concentration at which the reaction rate is at half Vmax. A competitive inhibitor can be outcompeted by adding additional substrate; thus Vmax is unaffected, since it can be accomplished with enough additional substrate. However, since we need to add additional substrate to compete with the inhibitor to get the reaction to the same rate, our Km increases.
Competitive inhibitors bind to the active site of the target enzyme. Km is the substrate concentration at which the reaction rate is at half Vmax. A competitive inhibitor can be outcompeted by adding additional substrate; thus Vmax is unaffected, since it can be accomplished with enough additional substrate. However, since we need to add additional substrate to compete with the inhibitor to get the reaction to the same rate, our Km increases.
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