Citric Acid Cycle Energetics - Biochemistry
Card 1 of 28
Which of the following steps in the citric acid cycle do not have a largely negative 
?
Which of the following steps in the citric acid cycle do not have a largely negative
Tap to reveal answer
Even though an 
is generated when malate is dehydrogenated to oxaloacetate, this oxidation is very unfavorable because of the addition of a reactive ketone in place of an alcohol on the 2nd carbon. In fact, the only way this reaction can proceed is if oxaloacetate concentration is very low. All of the other reactions have large negative 
values.
Even though an
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Which of the following statements about the citric acid cycle is true?
Which of the following statements about the citric acid cycle is true?
Tap to reveal answer
Acetyl-CoA is not part of the cycle but is oxidized by it. There are two decarboxylations in the cycle, from isocitrate to alpha-ketoglutarate, and from alpha-ketoglutarate to succinyl-CoA. In total, three equivalents of 
are produced in the cycle. Isocitrate is a compound in the cycle, produced from citrate.
Acetyl-CoA is not part of the cycle but is oxidized by it. There are two decarboxylations in the cycle, from isocitrate to alpha-ketoglutarate, and from alpha-ketoglutarate to succinyl-CoA. In total, three equivalents of
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Which reaction of the citric acid cycle makes the entire process unidirectional (i.e. irreversible)?
Which reaction of the citric acid cycle makes the entire process unidirectional (i.e. irreversible)?
Tap to reveal answer
The formation of alpha-ketoglutarate from isocitrate using the enzyme alpha-ketoglutarate dehydrogenase is an irreversible reaction due to its largely negative 
value.
The formation of alpha-ketoglutarate from isocitrate using the enzyme alpha-ketoglutarate dehydrogenase is an irreversible reaction due to its largely negative
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Suppose that in a certain neuron, an action potential has caused 
ions to enter the cell. In order to restore the resting membrane potential, the sodium-potassium pump uses 1 molecule of ATP to push 
ions out of the cell and to bring 
ions into the cell. How many molecules of acetyl-CoA must pass through the citric acid cycle in order to provide enough energy for this process to occur?
Suppose that in a certain neuron, an action potential has caused
Tap to reveal answer
This question is providing us with a scenario in which 
ions enter a cell. We're further told that it will take a single molecule of ATP to move three of these ions out of the cell. Finally, we are being asked to determine the total number of acetyl-CoA molecules that must pass through the Krebs cycle in order to provide the energy necessary for the export of these 
ions.
First, we'll need to determine the total number of ATP molecules generated from the passage of a single molecule of acetyl-CoA through the Krebs cycle. It's important to remember that the passage of acetyl-CoA through the Krebs cycle generates one molecule of ATP directly by substrate-level phosphorylation, but it also produces other intermediate energy carriers in the form of 
and 
.
For each acetyl-CoA ran through the cycle, one molecule of 
and three molecules of 
are produced. Furthermore, each molecule of 
will go on to donate its electrons to the electron transport chain to generate 
molecules of ATP per molecule of 
oxidized. Likewise, each 
will also produce ATP via oxidative phosphorylation, but at a rate of 
molecules of ATP per molecule of 
oxidized.
Adding these up, we obtain:
ATP via substrate-level phosphorylation
Adding these values up, we have a total of 
molecules of ATP produced for every molecule of acetyl-CoA oxidized. Now that we know how much ATP is produced from one acetyl-CoA, we can calculate the number needed to move the 
ions out of the cell.
This question is providing us with a scenario in which
First, we'll need to determine the total number of ATP molecules generated from the passage of a single molecule of acetyl-CoA through the Krebs cycle. It's important to remember that the passage of acetyl-CoA through the Krebs cycle generates one molecule of ATP directly by substrate-level phosphorylation, but it also produces other intermediate energy carriers in the form of
For each acetyl-CoA ran through the cycle, one molecule of
Adding these up, we obtain:
Adding these values up, we have a total of
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Which of the following steps within the citric acid cycle directly produces ATP (or GTP) as a side product?
Which of the following steps within the citric acid cycle directly produces ATP (or GTP) as a side product?
Tap to reveal answer
The only step of the citric acid cycle (also known as the Krebs cycle, or the TCA cycle) that directly produces ATP or GTP is the conversion of succinyl-CoA to succinate.
In this reaction, succinyl-CoA is converted to succinate with the assistance of the enzyme, succinyl-CoA synthetase. During this reaction, ADP + Pi (or GDP + Pi) is also converted to ATP (or GTP) using the energy from the breaking of the bond between CoA and succinate. Thus, the overall reaction appears as:
While side products of some of the other reactions listed produce intermediaries that may be used to produce ATP in the future, these reactions do not directly produce ATP.
The only step of the citric acid cycle (also known as the Krebs cycle, or the TCA cycle) that directly produces ATP or GTP is the conversion of succinyl-CoA to succinate.
In this reaction, succinyl-CoA is converted to succinate with the assistance of the enzyme, succinyl-CoA synthetase. During this reaction, ADP + Pi (or GDP + Pi) is also converted to ATP (or GTP) using the energy from the breaking of the bond between CoA and succinate. Thus, the overall reaction appears as:
While side products of some of the other reactions listed produce intermediaries that may be used to produce ATP in the future, these reactions do not directly produce ATP.
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Which of the following steps within the citric acid cycle does not produce 
as a side product?
Which of the following steps within the citric acid cycle does not produce
Tap to reveal answer
The only citric acid cycle (also known as the Krebs cycle or TCA cycle) step listed that does not result in the production of 
as a side product is the conversion of fumarate to malate.
In the conversion of fumarate to malate, fumarate is chemically combined with water in the presence of the enzyme fumarase to produce malate. In this conversion, there is no concomitant production of 
.
In each of the other reactions listed, 
is converted to 
and 
as side products.
The only citric acid cycle (also known as the Krebs cycle or TCA cycle) step listed that does not result in the production of
In the conversion of fumarate to malate, fumarate is chemically combined with water in the presence of the enzyme fumarase to produce malate. In this conversion, there is no concomitant production of
In each of the other reactions listed,
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Which of the following steps of the citric acid cycle results in the production of 
as a side product?
Which of the following steps of the citric acid cycle results in the production of
Tap to reveal answer
The correct answer is that none of the citric acid cycle steps listed result in the production of 
. The only step of the citric acid cycle that results in the production of 
is the conversion of succinate to fumarate (catalyzed by succinate dehydrogenase). In this reaction, 
is concomitantly converted to 
using the hydrogen molecules removed from succinate by succinate dehydrogenase. This reaction was not listed in the answer choices though, and therefore none of the reactions listed produced 
.
Each of the reactions listed did produce other side products. The conversions of isocitrate to alpha-ketoglutarate, alpha-ketoglutarate to succinyl-CoA, and malate to oxaloacetate all result in the production of 
as a side product, but not 
. The conversion of succinyl-CoA to succinate results in the production of ATP or GTP and CoA-SH as side products, but not 
.
The correct answer is that none of the citric acid cycle steps listed result in the production of
Each of the reactions listed did produce other side products. The conversions of isocitrate to alpha-ketoglutarate, alpha-ketoglutarate to succinyl-CoA, and malate to oxaloacetate all result in the production of
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Which of the following steps in the citric acid cycle do not have a largely negative ?
Which of the following steps in the citric acid cycle do not have a largely negative
Tap to reveal answer
Even though an is generated when malate is dehydrogenated to oxaloacetate, this oxidation is very unfavorable because of the addition of a reactive ketone in place of an alcohol on the 2nd carbon. In fact, the only way this reaction can proceed is if oxaloacetate concentration is very low. All of the other reactions have large negative values.
Even though an
← Didn't Know|Knew It →
Which of the following statements about the citric acid cycle is true?
Which of the following statements about the citric acid cycle is true?
Tap to reveal answer
Acetyl-CoA is not part of the cycle but is oxidized by it. There are two decarboxylations in the cycle, from isocitrate to alpha-ketoglutarate, and from alpha-ketoglutarate to succinyl-CoA. In total, three equivalents of are produced in the cycle. Isocitrate is a compound in the cycle, produced from citrate.
Acetyl-CoA is not part of the cycle but is oxidized by it. There are two decarboxylations in the cycle, from isocitrate to alpha-ketoglutarate, and from alpha-ketoglutarate to succinyl-CoA. In total, three equivalents of
← Didn't Know|Knew It →
Which reaction of the citric acid cycle makes the entire process unidirectional (i.e. irreversible)?
Which reaction of the citric acid cycle makes the entire process unidirectional (i.e. irreversible)?
Tap to reveal answer
The formation of alpha-ketoglutarate from isocitrate using the enzyme alpha-ketoglutarate dehydrogenase is an irreversible reaction due to its largely negative value.
The formation of alpha-ketoglutarate from isocitrate using the enzyme alpha-ketoglutarate dehydrogenase is an irreversible reaction due to its largely negative
← Didn't Know|Knew It →
Suppose that in a certain neuron, an action potential has caused ions to enter the cell. In order to restore the resting membrane potential, the sodium-potassium pump uses 1 molecule of ATP to push ions out of the cell and to bring ions into the cell. How many molecules of acetyl-CoA must pass through the citric acid cycle in order to provide enough energy for this process to occur?
Suppose that in a certain neuron, an action potential has caused
Tap to reveal answer
This question is providing us with a scenario in which ions enter a cell. We're further told that it will take a single molecule of ATP to move three of these ions out of the cell. Finally, we are being asked to determine the total number of acetyl-CoA molecules that must pass through the Krebs cycle in order to provide the energy necessary for the export of these ions.
First, we'll need to determine the total number of ATP molecules generated from the passage of a single molecule of acetyl-CoA through the Krebs cycle. It's important to remember that the passage of acetyl-CoA through the Krebs cycle generates one molecule of ATP directly by substrate-level phosphorylation, but it also produces other intermediate energy carriers in the form of and .
For each acetyl-CoA ran through the cycle, one molecule of and three molecules of are produced. Furthermore, each molecule of will go on to donate its electrons to the electron transport chain to generate molecules of ATP per molecule of oxidized. Likewise, each will also produce ATP via oxidative phosphorylation, but at a rate of molecules of ATP per molecule of oxidized.
Adding these up, we obtain:
ATP via substrate-level phosphorylation
Adding these values up, we have a total of molecules of ATP produced for every molecule of acetyl-CoA oxidized. Now that we know how much ATP is produced from one acetyl-CoA, we can calculate the number needed to move the ions out of the cell.
This question is providing us with a scenario in which
First, we'll need to determine the total number of ATP molecules generated from the passage of a single molecule of acetyl-CoA through the Krebs cycle. It's important to remember that the passage of acetyl-CoA through the Krebs cycle generates one molecule of ATP directly by substrate-level phosphorylation, but it also produces other intermediate energy carriers in the form of
For each acetyl-CoA ran through the cycle, one molecule of
Adding these up, we obtain:
Adding these values up, we have a total of
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Which of the following steps within the citric acid cycle directly produces ATP (or GTP) as a side product?
Which of the following steps within the citric acid cycle directly produces ATP (or GTP) as a side product?
Tap to reveal answer
The only step of the citric acid cycle (also known as the Krebs cycle, or the TCA cycle) that directly produces ATP or GTP is the conversion of succinyl-CoA to succinate.
In this reaction, succinyl-CoA is converted to succinate with the assistance of the enzyme, succinyl-CoA synthetase. During this reaction, ADP + Pi (or GDP + Pi) is also converted to ATP (or GTP) using the energy from the breaking of the bond between CoA and succinate. Thus, the overall reaction appears as:
While side products of some of the other reactions listed produce intermediaries that may be used to produce ATP in the future, these reactions do not directly produce ATP.
The only step of the citric acid cycle (also known as the Krebs cycle, or the TCA cycle) that directly produces ATP or GTP is the conversion of succinyl-CoA to succinate.
In this reaction, succinyl-CoA is converted to succinate with the assistance of the enzyme, succinyl-CoA synthetase. During this reaction, ADP + Pi (or GDP + Pi) is also converted to ATP (or GTP) using the energy from the breaking of the bond between CoA and succinate. Thus, the overall reaction appears as:
While side products of some of the other reactions listed produce intermediaries that may be used to produce ATP in the future, these reactions do not directly produce ATP.
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Which of the following steps within the citric acid cycle does not produce as a side product?
Which of the following steps within the citric acid cycle does not produce
Tap to reveal answer
The only citric acid cycle (also known as the Krebs cycle or TCA cycle) step listed that does not result in the production of as a side product is the conversion of fumarate to malate.
In the conversion of fumarate to malate, fumarate is chemically combined with water in the presence of the enzyme fumarase to produce malate. In this conversion, there is no concomitant production of .
In each of the other reactions listed, is converted to and as side products.
The only citric acid cycle (also known as the Krebs cycle or TCA cycle) step listed that does not result in the production of
In the conversion of fumarate to malate, fumarate is chemically combined with water in the presence of the enzyme fumarase to produce malate. In this conversion, there is no concomitant production of
In each of the other reactions listed,
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Which of the following steps of the citric acid cycle results in the production of as a side product?
Which of the following steps of the citric acid cycle results in the production of
Tap to reveal answer
The correct answer is that none of the citric acid cycle steps listed result in the production of . The only step of the citric acid cycle that results in the production of is the conversion of succinate to fumarate (catalyzed by succinate dehydrogenase). In this reaction, is concomitantly converted to using the hydrogen molecules removed from succinate by succinate dehydrogenase. This reaction was not listed in the answer choices though, and therefore none of the reactions listed produced .
Each of the reactions listed did produce other side products. The conversions of isocitrate to alpha-ketoglutarate, alpha-ketoglutarate to succinyl-CoA, and malate to oxaloacetate all result in the production of as a side product, but not . The conversion of succinyl-CoA to succinate results in the production of ATP or GTP and CoA-SH as side products, but not .
The correct answer is that none of the citric acid cycle steps listed result in the production of
Each of the reactions listed did produce other side products. The conversions of isocitrate to alpha-ketoglutarate, alpha-ketoglutarate to succinyl-CoA, and malate to oxaloacetate all result in the production of
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Which of the following steps in the citric acid cycle do not have a largely negative ?
Which of the following steps in the citric acid cycle do not have a largely negative
Tap to reveal answer
Even though an is generated when malate is dehydrogenated to oxaloacetate, this oxidation is very unfavorable because of the addition of a reactive ketone in place of an alcohol on the 2nd carbon. In fact, the only way this reaction can proceed is if oxaloacetate concentration is very low. All of the other reactions have large negative values.
Even though an
← Didn't Know|Knew It →
Which of the following statements about the citric acid cycle is true?
Which of the following statements about the citric acid cycle is true?
Tap to reveal answer
Acetyl-CoA is not part of the cycle but is oxidized by it. There are two decarboxylations in the cycle, from isocitrate to alpha-ketoglutarate, and from alpha-ketoglutarate to succinyl-CoA. In total, three equivalents of are produced in the cycle. Isocitrate is a compound in the cycle, produced from citrate.
Acetyl-CoA is not part of the cycle but is oxidized by it. There are two decarboxylations in the cycle, from isocitrate to alpha-ketoglutarate, and from alpha-ketoglutarate to succinyl-CoA. In total, three equivalents of
← Didn't Know|Knew It →
Which reaction of the citric acid cycle makes the entire process unidirectional (i.e. irreversible)?
Which reaction of the citric acid cycle makes the entire process unidirectional (i.e. irreversible)?
Tap to reveal answer
The formation of alpha-ketoglutarate from isocitrate using the enzyme alpha-ketoglutarate dehydrogenase is an irreversible reaction due to its largely negative value.
The formation of alpha-ketoglutarate from isocitrate using the enzyme alpha-ketoglutarate dehydrogenase is an irreversible reaction due to its largely negative
← Didn't Know|Knew It →
Suppose that in a certain neuron, an action potential has caused ions to enter the cell. In order to restore the resting membrane potential, the sodium-potassium pump uses 1 molecule of ATP to push ions out of the cell and to bring ions into the cell. How many molecules of acetyl-CoA must pass through the citric acid cycle in order to provide enough energy for this process to occur?
Suppose that in a certain neuron, an action potential has caused
Tap to reveal answer
This question is providing us with a scenario in which ions enter a cell. We're further told that it will take a single molecule of ATP to move three of these ions out of the cell. Finally, we are being asked to determine the total number of acetyl-CoA molecules that must pass through the Krebs cycle in order to provide the energy necessary for the export of these ions.
First, we'll need to determine the total number of ATP molecules generated from the passage of a single molecule of acetyl-CoA through the Krebs cycle. It's important to remember that the passage of acetyl-CoA through the Krebs cycle generates one molecule of ATP directly by substrate-level phosphorylation, but it also produces other intermediate energy carriers in the form of and .
For each acetyl-CoA ran through the cycle, one molecule of and three molecules of are produced. Furthermore, each molecule of will go on to donate its electrons to the electron transport chain to generate molecules of ATP per molecule of oxidized. Likewise, each will also produce ATP via oxidative phosphorylation, but at a rate of molecules of ATP per molecule of oxidized.
Adding these up, we obtain:
ATP via substrate-level phosphorylation
Adding these values up, we have a total of molecules of ATP produced for every molecule of acetyl-CoA oxidized. Now that we know how much ATP is produced from one acetyl-CoA, we can calculate the number needed to move the ions out of the cell.
This question is providing us with a scenario in which
First, we'll need to determine the total number of ATP molecules generated from the passage of a single molecule of acetyl-CoA through the Krebs cycle. It's important to remember that the passage of acetyl-CoA through the Krebs cycle generates one molecule of ATP directly by substrate-level phosphorylation, but it also produces other intermediate energy carriers in the form of
For each acetyl-CoA ran through the cycle, one molecule of
Adding these up, we obtain:
Adding these values up, we have a total of
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Which of the following steps within the citric acid cycle directly produces ATP (or GTP) as a side product?
Which of the following steps within the citric acid cycle directly produces ATP (or GTP) as a side product?
Tap to reveal answer
The only step of the citric acid cycle (also known as the Krebs cycle, or the TCA cycle) that directly produces ATP or GTP is the conversion of succinyl-CoA to succinate.
In this reaction, succinyl-CoA is converted to succinate with the assistance of the enzyme, succinyl-CoA synthetase. During this reaction, ADP + Pi (or GDP + Pi) is also converted to ATP (or GTP) using the energy from the breaking of the bond between CoA and succinate. Thus, the overall reaction appears as:
While side products of some of the other reactions listed produce intermediaries that may be used to produce ATP in the future, these reactions do not directly produce ATP.
The only step of the citric acid cycle (also known as the Krebs cycle, or the TCA cycle) that directly produces ATP or GTP is the conversion of succinyl-CoA to succinate.
In this reaction, succinyl-CoA is converted to succinate with the assistance of the enzyme, succinyl-CoA synthetase. During this reaction, ADP + Pi (or GDP + Pi) is also converted to ATP (or GTP) using the energy from the breaking of the bond between CoA and succinate. Thus, the overall reaction appears as:
While side products of some of the other reactions listed produce intermediaries that may be used to produce ATP in the future, these reactions do not directly produce ATP.
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Which of the following steps within the citric acid cycle does not produce as a side product?
Which of the following steps within the citric acid cycle does not produce
Tap to reveal answer
The only citric acid cycle (also known as the Krebs cycle or TCA cycle) step listed that does not result in the production of as a side product is the conversion of fumarate to malate.
In the conversion of fumarate to malate, fumarate is chemically combined with water in the presence of the enzyme fumarase to produce malate. In this conversion, there is no concomitant production of .
In each of the other reactions listed, is converted to and as side products.
The only citric acid cycle (also known as the Krebs cycle or TCA cycle) step listed that does not result in the production of
In the conversion of fumarate to malate, fumarate is chemically combined with water in the presence of the enzyme fumarase to produce malate. In this conversion, there is no concomitant production of
In each of the other reactions listed,
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