Catabolic Pathways and Metabolism - Biochemistry
Card 0 of 20
Which of the following is false about the structure and function of ATP synthase?
Which of the following is false about the structure and function of ATP synthase?
ATP synthase can indeed produce more than 100 ATP molecules per second, and in the process, it only requires a few -- three or four -- protons, per ATP. These protons pass down a gradient through the membrane. Hence, the protein is membrane-bound. The protons cause the rotor of 10-14 subunits to spin. The protein's head itself has six subunits, three of which have ADP binding and phosphate binding sites.
ATP synthase can indeed produce more than 100 ATP molecules per second, and in the process, it only requires a few -- three or four -- protons, per ATP. These protons pass down a gradient through the membrane. Hence, the protein is membrane-bound. The protons cause the rotor of 10-14 subunits to spin. The protein's head itself has six subunits, three of which have ADP binding and phosphate binding sites.
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What is the basic mechanism by which ATP synthase generates ATP in the mitochondria?
What is the basic mechanism by which ATP synthase generates ATP in the mitochondria?
The electron transport chain moves high energy electrons through its complexes in order to create a proton gradient across the mitochondrial inner membrane. The ATP synthase then uses this gradient to pass hydrogen atoms through it. Because this is a favorable movement, it can be coupled to unfavorable processes such as conversion of ADP to ATP.
The electron transport chain moves high energy electrons through its complexes in order to create a proton gradient across the mitochondrial inner membrane. The ATP synthase then uses this gradient to pass hydrogen atoms through it. Because this is a favorable movement, it can be coupled to unfavorable processes such as conversion of ADP to ATP.
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ATP synthase catalyzes which of the following reactions?
ATP synthase catalyzes which of the following reactions?
ATP synthase catalyzes the reaction that shows ADP and the phosphate group forming ATP. The hydrogen in the reactant side is the one involved in the proton gradient, and water is a byproduct of the reaction.
ATP synthase catalyzes the reaction that shows ADP and the phosphate group forming ATP. The hydrogen in the reactant side is the one involved in the proton gradient, and water is a byproduct of the reaction.
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Which of the following part(s) of ATP synthase is involved in catalysis?
Which of the following part(s) of ATP synthase is involved in catalysis?
ATP synthase is located in the inner mitochondrial membrane. It has an F0 portion within the membrane and an F1 portion in the matrix. The F1 portion has a hexameric ring structure and is responsible for the creation of ATP from mechanical energy. The alpha, beta, and gamma subunits are all parts of the F1 portion of ATP synthase, however it is only the alpha and beta subunits that form the ring. Further, the beta subunit is the part of the ring that is considered to be catalytic.
ATP synthase is located in the inner mitochondrial membrane. It has an F0 portion within the membrane and an F1 portion in the matrix. The F1 portion has a hexameric ring structure and is responsible for the creation of ATP from mechanical energy. The alpha, beta, and gamma subunits are all parts of the F1 portion of ATP synthase, however it is only the alpha and beta subunits that form the ring. Further, the beta subunit is the part of the ring that is considered to be catalytic.
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What happens during stage 1 of the Calvin cycle?
What happens during stage 1 of the Calvin cycle?
All of the answer choices are steps in the Calvin cycle, but the only one that describes the first stage - fixation - is 
and ribulose 1,5-bisphosphate reacting to form 3-phosphoglycerate.
All of the answer choices are steps in the Calvin cycle, but the only one that describes the first stage - fixation - is
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What vitamin does pyruvate dehydrogenase need in order to make pyruvate into acetyl-CoA for the citric acid cycle?
What vitamin does pyruvate dehydrogenase need in order to make pyruvate into acetyl-CoA for the citric acid cycle?
Thiamine (B1) acts as a cofactor to enable pyruvate dehydrogenase to convert pyruvate from glycolysis into acetyl-CoA so it can enter the citric acid cycle.
Thiamine (B1) acts as a cofactor to enable pyruvate dehydrogenase to convert pyruvate from glycolysis into acetyl-CoA so it can enter the citric acid cycle.
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Pyruvate enters the citric acid cycle after being converted to a molecule with how many carbons?
Pyruvate enters the citric acid cycle after being converted to a molecule with how many carbons?
The three-carbon molecule pyruvate produced from glycolysis is converted to the two-carbon molecule acetyl-coenzyme A (acetyl-CoA). This is carried out by a combination of three enzymes collectively known as the pyruvate dehydrogenase complex. The conversion of pyruvate to acetyl-CoA produces one 
. Acetyl-CoA has one less carbon than pyruvate; this third carbon from pyruvate was lost as carbon dioxide during its conversion to acetyl-CoA via the pyruvate dehydrogenase complex.
The three-carbon molecule pyruvate produced from glycolysis is converted to the two-carbon molecule acetyl-coenzyme A (acetyl-CoA). This is carried out by a combination of three enzymes collectively known as the pyruvate dehydrogenase complex. The conversion of pyruvate to acetyl-CoA produces one
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Which molecule is not a citric acid cycle intermediate?
Which molecule is not a citric acid cycle intermediate?
Phosphoenolpyruvate (PEP) is an intermediate in glycolysis, not the citric acid cycle. PEP is the product of the ninth reaction in glycolysis, which involves the enolase-catalyzed conversion of 2-phosphoglycerate into PEP. All other molecules are indeed intermediates in the citric acid cycle.
Phosphoenolpyruvate (PEP) is an intermediate in glycolysis, not the citric acid cycle. PEP is the product of the ninth reaction in glycolysis, which involves the enolase-catalyzed conversion of 2-phosphoglycerate into PEP. All other molecules are indeed intermediates in the citric acid cycle.
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What is the intermediate between citrate and isocitrate?
What is the intermediate between citrate and isocitrate?
The citric acid cycle begins when a four-carbon molecule, oxaloacetate combines with acetyl-CoA (a two carbon molecule) to produce the six-carbon molecule citrate. The enzyme citrate synthase carries out this reaction. Citrate then becomes the six-carbon molecule cis-aconitate via catalysis by aconitase. The same enzyme then converts cis-aconitate to isocitrate, which is an isomer of citrate.
The citric acid cycle begins when a four-carbon molecule, oxaloacetate combines with acetyl-CoA (a two carbon molecule) to produce the six-carbon molecule citrate. The enzyme citrate synthase carries out this reaction. Citrate then becomes the six-carbon molecule cis-aconitate via catalysis by aconitase. The same enzyme then converts cis-aconitate to isocitrate, which is an isomer of citrate.
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The citric acid cycle begins when the two-carbon acetyl group from acetyl-CoA combines with the four-carbon molecule __________ to form the six-carbon molecule citrate.
The citric acid cycle begins when the two-carbon acetyl group from acetyl-CoA combines with the four-carbon molecule __________ to form the six-carbon molecule citrate.
Oxaloacetate combines with acetyl-CoA to form citrate. This is the first stage of the citric acid cycle. Eventually, citrate will lose two molecules of 
to regenerate the four-carbon molecule oxaloacetate.
Oxaloacetate combines with acetyl-CoA to form citrate. This is the first stage of the citric acid cycle. Eventually, citrate will lose two molecules of
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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.
During strenuous exercise, GLUT4 will be highly active. Which of the following intermediates will also increase?
I. Pyruvate
II. 
III. ADP
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
During strenuous exercise, GLUT4 will be highly active. Which of the following intermediates will also increase?
I. Pyruvate
II.
III. ADP
During strenuous exercise, GLUT4 will be active to bring glucose into the cell. Glucose is then pushed through glycolysis to generate pyruvate. Pyruvate is then pushed through pyruvate dehydrogenase complex, where it is converted into acetyl-CoA, which feeds into the Krebs cycle (assuming aerobic conditions) to generate ATP, NADH, 
, and carbon dioxide.
During strenuous exercise, GLUT4 will be active to bring glucose into the cell. Glucose is then pushed through glycolysis to generate pyruvate. Pyruvate is then pushed through pyruvate dehydrogenase complex, where it is converted into acetyl-CoA, which feeds into the Krebs cycle (assuming aerobic conditions) to generate ATP, NADH,
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Which of the following Krebs cycle intermediate molecules can be used directly in another pathway to make fatty acids?
Which of the following Krebs cycle intermediate molecules can be used directly in another pathway to make fatty acids?
Most of the intermediate molecules in the Krebs cycle can, rather than continuing through the cycle itself, go through other pathways to form macromolecules. Citrate can be used to create fatty acids and sterols. Alph-ketoglutarate can be used to make some of the amino acids. Succinyl-CoA can be used to make porphyrins, heme, and chlorophyll. Aspartate can be used to make some of the amino acids. Oxaloacetate can be used in gluconeogenesis to create glucose.
Most of the intermediate molecules in the Krebs cycle can, rather than continuing through the cycle itself, go through other pathways to form macromolecules. Citrate can be used to create fatty acids and sterols. Alph-ketoglutarate can be used to make some of the amino acids. Succinyl-CoA can be used to make porphyrins, heme, and chlorophyll. Aspartate can be used to make some of the amino acids. Oxaloacetate can be used in gluconeogenesis to create glucose.
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How many atoms of carbon are present in the citric acid cycle intermediate, fumarate?
How many atoms of carbon are present in the citric acid cycle intermediate, fumarate?
The citric acid cycle intermediate, fumarate, contains four atoms of carbon.
As a frame of reference, one molecule of glucose, the starting material for glycolysis, contains six atoms of carbon. The carbohydrate products of glycolysis are two molecules of pyruvate, with one molecule of pyruvate containing three atoms of carbon.
In preparation for entering the citric acid cycle, pyruvate loses one molecule of carbon dioxide, and therefore one molecule of carbon, to form acetyl-CoA, which contains two atoms of carbon. Acetyl-CoA is then combined with a molecule of oxaloacetate, which contains four atoms of carbon, to produce a molecule of citrate, which contains six atoms of carbon, and is the starting point for the citric acid cycle.
Citrate undergoes a number of a reactions, via the citric acid cycle, most notably two reactions in which a single molecule of carbon dioxide, and therefore carbon, is lost, thereby decreasing the total number of carbons to four atoms. The two reactions that remove carbons are the conversion of isocitrate to alpha-ketoglutarate and the conversion of alpha-ketoglutarate to succinyl-CoA. No additional carbons are removed prior to the production of fumarate, and therefore, fumarate contains four atoms of carbon.
The citric acid cycle intermediate, fumarate, contains four atoms of carbon.
As a frame of reference, one molecule of glucose, the starting material for glycolysis, contains six atoms of carbon. The carbohydrate products of glycolysis are two molecules of pyruvate, with one molecule of pyruvate containing three atoms of carbon.
In preparation for entering the citric acid cycle, pyruvate loses one molecule of carbon dioxide, and therefore one molecule of carbon, to form acetyl-CoA, which contains two atoms of carbon. Acetyl-CoA is then combined with a molecule of oxaloacetate, which contains four atoms of carbon, to produce a molecule of citrate, which contains six atoms of carbon, and is the starting point for the citric acid cycle.
Citrate undergoes a number of a reactions, via the citric acid cycle, most notably two reactions in which a single molecule of carbon dioxide, and therefore carbon, is lost, thereby decreasing the total number of carbons to four atoms. The two reactions that remove carbons are the conversion of isocitrate to alpha-ketoglutarate and the conversion of alpha-ketoglutarate to succinyl-CoA. No additional carbons are removed prior to the production of fumarate, and therefore, fumarate contains four atoms of carbon.
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How many molecules of carbon are present in the citric acid cycle intermediate, malate?
How many molecules of carbon are present in the citric acid cycle intermediate, malate?
The citric acid cycle intermediate, malate, contains four atoms of carbon.
A single glucose molecule, which is the starting material for glycolysis, contains six carbon atoms. Glycolysis produces two pyruvate molecules, and one pyruvate molecule contains three carbon atoms.
Prior to entering the citric acid cycle, pyruvate loses one carbon dioxide molecule (e.g. one carbon atom), forming acetyl-CoA, which contains two carbon atoms. Acetyl-CoA then combines with one oxaloacetate molecule, a **four-**carbon molecule, to produce a molecule of citrate, which contains six carbon atoms, and is the starting material for the citric acid cycle.
Citrate undergoes a number of a reactions in the citric acid cycle, including two reactions where one atom of carbon dioxide (e.g. carbon) is lost, which decreases the total number of carbons to four atoms. The two reactions that remove carbons are the conversion of isocitrate to alpha-ketoglutarate and the conversion of alpha-ketoglutarate to succinyl-CoA. No additional carbons are removed prior to the production of malate. Therefore, malate contains four atoms of carbon.
The citric acid cycle intermediate, malate, contains four atoms of carbon.
A single glucose molecule, which is the starting material for glycolysis, contains six carbon atoms. Glycolysis produces two pyruvate molecules, and one pyruvate molecule contains three carbon atoms.
Prior to entering the citric acid cycle, pyruvate loses one carbon dioxide molecule (e.g. one carbon atom), forming acetyl-CoA, which contains two carbon atoms. Acetyl-CoA then combines with one oxaloacetate molecule, a **four-**carbon molecule, to produce a molecule of citrate, which contains six carbon atoms, and is the starting material for the citric acid cycle.
Citrate undergoes a number of a reactions in the citric acid cycle, including two reactions where one atom of carbon dioxide (e.g. carbon) is lost, which decreases the total number of carbons to four atoms. The two reactions that remove carbons are the conversion of isocitrate to alpha-ketoglutarate and the conversion of alpha-ketoglutarate to succinyl-CoA. No additional carbons are removed prior to the production of malate. Therefore, malate contains four atoms of carbon.
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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
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?
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)?
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
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?
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
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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