EX01_05
Acetyl-CoA, on the other hand, derived from pyruvate oxidation, or from the beta-oxidation of fatty acids, is the only fuel to enter the citric acid cycle. With each turn of the cycle one molecule of acetyl-CoA is consumed for every molecule of oxaloacetate present in the mitochondrial matrix, and is never regenerated. It is the oxidation of the acetate portion of acetyl-CoA that produces CO2 and water, with the energy thus released captured in the form of ATP.[31]
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At the end of each cycle, the four-carbon oxaloacetate has been regenerated, and the cycle continues.
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Calcium is used as a regulator. Mitochondrial matrix calcium levels can reach the tens of micromolar levels during cellular activation.[27] It activates pyruvate dehydrogenase phosphatase which in turn activates the pyruvate dehydrogenase complex. Calcium also activates isocitrate dehydrogenase and α-ketoglutarate dehydrogenase.[28] This increases the reaction rate of many of the steps in the cycle, and therefore increases flux throughout the pathway.
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Citrate is used for feedback inhibition, as it inhibits phosphofructokinase, an enzyme involved in glycolysis that catalyses formation of fructose 1,6-bisphosphate,a precursor of pyruvate. This prevents a constant high rate of flux when there is an accumulation of citrate and a decrease in substrate for the enzyme.
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Electrons are also transferred to the electron acceptor Q, forming QH2.
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However, it is also possible for pyruvate to be carboxylated by pyruvate carboxylase to form oxaloacetate. This latter reaction "fills up" the amount of oxaloacetate in the citric acid cycle, and is therefore an anaplerotic reaction, increasing the cycle's capacity to metabolize acetyl-CoA when the tissue's energy needs (e.g. in muscle) are suddenly increased by activity.[31
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In the citric acid cycle all the intermediates (e.g. citrate, iso-citrate, alpha-ketoglutarate, succinate, fumarate, malate and oxaloacetate) are regenerated during each turn of the cycle. Adding more of any of these intermediates to the mitochondrion therefore means that that additional amount is retained within the cycle, increasing all the other intermediates as one is converted into the other. Hence the addition of any one of them to the cycle has an anaplerotic effect, and its removal has a cataplerotic effect. These anaplerotic and cataplerotic reactions will, during the course of the cycle, increase or decrease the amount of oxaloacetate available to combine with acetyl-CoA to form citric acid. This in turn increases or decreases the rate of ATP production by the mitochondrion, and thus the availability of ATP to the cell.[31]
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Most of the energy made available by the oxidative steps of the cycle is transferred as energy-rich electrons to NAD+, forming NADH. For each acetyl group that enters the citric acid cycle, three molecules of NADH are produced.
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Pyruvate molecules produced by glycolysis are actively transported across the inner mitochondrial membrane, and into the matrix. Here they can be oxidized and combined with coenzyme A to form CO2, acetyl-CoA, and NADH, as in the normal cycle.[30]
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Several catabolic pathways converge on the TCA cycle. Most of these reactions add intermediates to the TCA cycle, and are therefore known as anaplerotic reactions, from the Greek meaning to "fill up". These increase the amount of acetyl CoA that the cycle is able to carry, increasing the mitochondrion's capability to carry out respiration if this is otherwise a limiting factor. Processes that remove intermediates from the cycle are termed "cataplerotic" reactions.
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The citrate then goes through a series of chemical transformations, losing two carboxyl groups as CO2. The carbons lost as CO2 originate from what was oxaloacetate, not directly from acetyl-CoA. The carbons donated by acetyl-CoA become part of the oxaloacetate carbon backbone after the first turn of the citric acid cycle. Loss of the acetyl-CoA-donated carbons as CO2 requires several turns of the citric acid cycle. However, because of the role of the citric acid cycle in anabolism, they might not be lost, since many TCA cycle intermediates are also used as precursors for the biosynthesis of other molecules.[10]
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The citric acid cycle is continuously supplied with new carbon in the form of acetyl-CoA, entering at step 0
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The major eventual substrate of the cycle is ADP which gets converted to ATP. A reduced amount of ADP causes accumulation of precursor NADH which in turn can inhibit a number of enzymes. NADH, a product of all dehydrogenases in the TCA cycle with the exception of succinate dehydrogenase, inhibits pyruvate dehydrogenase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and also citrate synthase. Acetyl-coA inhibits pyruvate dehydrogenase, while succinyl-CoA inhibits alpha-ketoglutarate dehydrogenase and citrate synthase.
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The regulation of the TCA cycle is largely determined by product inhibition and substrate availability. If the cycle were permitted to run unchecked, large amounts of metabolic energy could be wasted in overproduction of reduced coenzyme such as NADH and ATP.
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The theoretical maximum yield of ATP through oxidation of one molecule of glucose in glycolysis, citric acid cycle, and oxidative phosphorylation is 38 (assuming 3 molar equivalents of ATP per equivalent NADH and 2 ATP per FADH2). In eukaryotes, two equivalents of NADH are generated in glycolysis, which takes place in the cytoplasm. Transport of these two equivalents into the mitochondria consumes two equivalents of ATP, thus reducing the net production of ATP to 36. Furthermore, inefficiencies in oxidative phosphorylation due to leakage of protons across the mitochondrial membrane and slippage of the ATP synthase/proton pump commonly reduces the ATP yield from NADH and FADH2 to less than the theoretical maximum yield.[15] The observed yields are, therefore, closer to ~2.5 ATP per NADH and ~1.5 ATP per FADH2, further reducing the total net production of ATP to approximately 30.[16] An assessment of the total ATP yield with newly revised proton-to-ATP ratios provides an estimate of 29.85 ATP per glucose molecule.[17]
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Exhibit 19A The following compounds are all intermediates in the citric acid cycle. Refer to Exhibit 19A. Which intermediate is formed from acetyl-CoA and oxaloacetate. A. 1 B. 2 C. 3 D. 4 E. 5
A. 1
Which of these enzymes is most similar to pyruvate dehydrogenase? A. Alpha-Ketoglutarate Dehydrogenase complex. B. IsoCitrate Dehydrogenase. C. Succinate Dehydrogenase. D. Malate Dehydrogenase. E. None of these enzymes is similar to pyruvate dehydrogenase.
A. Alpha-Ketoglutarate Dehydrogenase complex.
Which group of small molecules best fit the boxes associated with the reaction shown? a b I. NAD+ NADH II. NADP+ NADPH III. ADP + Pi ATP IV. FAD FADH2 A. I B. II C. III D. IV
A. I
Which of the following is true regarding the control of pyruvate dehydrogenase? A. It is inhibited by ATP B. It is inhibited by NAD+ C. It is activated by acetyl-CoA D. It is inhibited by succinyl-CoA E. none of these are true
A. It is inhibited by ATP
Each of the enzymes of the pyruvate dehydrogenase complex requires a different vitamin. A. True B. False
A. True
Glyoxysomes are named for the fact that they contain the glyoxylate pathway. A. True B. False
A. True
The "energy charge" in a cell is important in the control of metabolism. A. True B. False
A. True
The production of malate in the glyoxylate pathway is important, since it can be readily converted to phosphoenolpyruvate and then to sugars. A. True B. False
A. True
Weight loss in humans can be difficult to achieve, since we lack the ability to convert our fats to sugars, and it is difficult to change our metabolism to using fats as a primary energy source. A. True B. False
A. True
When the citric acid cycle is not functioning, the most common fate of acetyl-CoA from sugar metabolism in humans is the formation of fatty acids or cholesterol. A. True B. False
A. True
When acetyl-CoA reacts with oxaloacetate to form citrate A. a new carbon-carbon bond is formed B. an oxidative decarboxylation reaction takes place C. a dehydration reaction takes place D. a rearrangement takes place
A. a new carbon-carbon bond is formed
The reactions in which succinate is converted to oxaloacetate are, in order A. an oxidation, a dehydration, and an oxidation B. three successive oxidation reactions C. an oxidative decarboxylation, a dehydration, and a condensation D. a condensation, a dehydration, and an oxidative decarboxylation
A. an oxidation, a dehydration, and an oxidation
The intracellular site of the glyoxylate cycle is A. glyoxysomes only. B. glyoxysomes and lysosomes. C. glyoxysomes and Golgi apparatus. D. glyoxysomes and smooth endoplasmic reticulum.
A. glyoxysomes only.
Which of the following enzymes is allosterically activated by NAD+? A. isocitrate dehydrogenase B. succinyl-CoA synthetase C. succinate dehydrogenase D. fumarase
A. isocitrate dehydrogenase
Which enzymes in the citric acid cycle catalyze oxidative decarboxylation reactions? A. isocitrate dehydrogenase and the a-ketoglutarate dehydrogenase complex B. aconitase and succinate dehydrogenase C. the a-ketoglutarate dehydrogenase complex and succinate thiokinase D. fumarase and succinate dehydrogenase
A. isocitrate dehydrogenase and the a-ketoglutarate dehydrogenase complex
The citric acid cycle is amphibolic, meaning A. it plays a role in both anabolism and catabolism. B. it is essentially irreversible. C. it can operate both in the presence and absence of oxygen. D. it can oxidize carbons and nitrogens equally well.
A. it plays a role in both anabolism and catabolism.
Which of the following enzymes is allosterically inhibited by ATP? A. pyruvate dehydrogenase complex B. succinyl-CoA synthetase C. succinate dehydrogenase D. fumarase
A. pyruvate dehydrogenase complex
Which enzyme catalyzes the reaction shown? A. succinyl-CoA synthetase B. succinate dehydrogenase C. pyruvate dehydrogenase D. a-ketoglutarate dehydrogenase
A. succinyl-CoA synthetase
The citric acid cycle is considered part of aerobic metabolism even though oxygen does not appear explicitly in any reaction because A. the NADH and FADH2 produced are reoxidized in the electron transport chain linked to oxygen B. the reoxidation of NADH and FADH2 leads to the production of considerable quantities of ATP C. it takes place in the mitochondrion D. it contains oxidation reactions
A. the NADH and FADH2 produced are reoxidized in the electron transport chain linked to oxygen
A control point outside the citric acid cycle is the reaction catalyzed by A. the pyruvate dehydrogenase complex. B. citrate synthetase. C. isocitrate dehydrogenase. D. the a-ketoglutarate dehydrogenase complex.
A. the pyruvate dehydrogenase complex.
Thiamine pyrophosphate carries a ____ carbon unit. A. 1 B. 2 C. 3 D. 4
B. 2
Intermediates of the citric acid cycle are especially important in the synthesis of fatty acids and amino acids. A. True B. False
B. False
Lipoic acid is a required vitamin in the human diet. A. True B. False
B. False
One round of the citric acid cycle generates about ten equivalents of ATP. A. True B. False
B. False
The citric acid cycle is the only metabolic pathway that can be used both as an anabolic and as a catabolic pathway. A. True B. False
B. False
The citric acid cycle uses anaplerotic reactions to get rid of the many intermediates of the cycle that accumulate during catabolism of amino acids. A. True B. False
B. False
The enzyme "aconitase" is also known as "condensing enzyme" A. True B. False
B. False
The iron ion, which is part of succinate dehydrogenase, is bonded to heme. A. True B. False
B. False
The only difference between succinate and fumarate is the geometry around their double bonds, one contains a cis double bond and the other contains a trans double bond. A. True B. False
B. False
Which group of small molecules best fit the boxes associated with the reaction shown? a b I. ADP + 2 Pi ATP II. NAD+ NADH III. NADP+ NADPH IV. FAD FADH2 A. I B. II C. III D. IV
B. II
The immediate electron acceptor for the majority of the oxidative reactions of the citric acid cycle is A. ATP. B. NAD. C. FAD. D. coenzyme A.
B. NAD.
There is a cyclic reaction in which pyruvate becomes oxaloacetate. The oxaloacetate is converted to malate and then back to pyruvate. This cycle is important because: A. There is no net use or fixation of CO2 in this cycle. B. NADH is converted to NADPH in this cycle. C. There is no net oxidation or reduction in this cycle. D. NADPH is converted to NADH in this cycle. E. This is actually a wasteful pathway with no practical use.
B. NADH is converted to NADPH in this cycle.
Which of the following is NOT a reaction occurring during oxidative decarboxylation of pyruvate? A. Removal of CO2. B. Oxidation of an acetate group. C. Addition of Coenzyme A to a 2-carbon fragment. D. Reduction of NAD+ E. All of these reactions take place during oxidative decarboxylation.
B. Oxidation of an acetate group. [correct] A. Removal of CO2. C. Addition of Coenzyme A to a 2-carbon fragment. D. Reduction of NAD+ E. All of these reactions take place during oxidative decarboxylation.
Release of succinate from succinyl-CoA can be coupled to GTP synthesis because: A. The amide bond between succinate and CoA has a large -DG of hydrolysis. B. The thioester bond between succinate and CoA has a large -DG of hydrolysis. C. The link between succinate and CoA involves an acid anhydride to phosphate. D. Coenzyme A is a "high energy" compound, just like GTP. E. None of these explains why GTP can be formed during this reaction.
B. The thioester bond between succinate and CoA has a large -DG of hydrolysis.
The conversion of citrate to isocitrate is remarkable because A. it is a condensation reaction. B. a chiral center is introduced in a molecule that did not have one previously. C. a dehydration reaction is involved. D. the enzyme that catalyzes it has very little specificity.
B. a chiral center is introduced in a molecule that did not have one previously.
The acetyl group is carried on lipoic acid as A. an alcohol. B. a thioester. C. a phosphoanhydride. D. an amide.
B. a thioester.
Which enzyme catalyzes the reaction shown? A. isocitrate dehydrogenase B. malate dehydrogenase C. fumarase D. succinate dehydrogenase
B. malate dehydrogenase
A unique feature of the glyoxylate cycle is that it allows the organisms that possess this pathway to A. produce fats from carbohydrates. B. produce carbohydrates from fats. C. convert acetyl-CoA to pyruvate. D. do all of the above.
B. produce carbohydrates from fats.
In which cellular location do the majority of the reactions of the citric acid cycle take place? A. the cytosol. B. the mitochondrial matrix. C. the endoplasmic reticulum. D. lysosomes.
B. the mitochondrial matrix.
An organism that undergoes the glyoxylate cycle can make sugar from fat because: A. there is a specific isomerase that converts a six carbon fatty acid to glucose B. the unique reactions of the glyoxylate cycle bypass the two decarboyxlation reactions of the citric acid cycle C. glyoxysomes lack succinate dehydrogenase D. none of these
B. the unique reactions of the glyoxylate cycle bypass the two decarboyxlation reactions of the citric acid cycle
The anaplerotic reactions associated with the citric acid cycle are the result of A. the oxidative nature of the citric acid cycle B. the use of many of the citric acid cycle intermediates in anabolism C. the decarboxylation reactions D. the production of GTP and reduced coenzymes
B. the use of many of the citric acid cycle intermediates in anabolism
Exhibit 19A The following compounds are all intermediates in the citric acid cycle. Refer to Exhibit 19A. Which intermediate becomes bonded to Coenzyme A during the cycle? A. 1 B. 2 C. 3 D. 4 E. 5
C. 3
Exhibit 19A The following compounds are all intermediates in the citric acid cycle. Refer to Exhibit 19A. Which intermediate does FAD oxidize? A. 2 B. 3 C. 4 D. 5 E. More than one of these is oxidized by FAD.
C. 4
"Energy charge" in a cell is a measure of A. ATP/NAD+ ratios. B. ATP/NADH ratios. C. ATP/ADP ratios. D. NADH/NAD+ ratios. E. NAD+/ADP ratios.
C. ATP/ADP ratios.
The order of compounds and intermediates found in the citric acid cycle is as follows: A. IsoCitrate ® Aconitate ® a-Ketoglutarate ® Fumarate ® Malate ® Oxaloacetate B. Aconitate ® IsoCitrate ® Oxaloacetate ® a-Ketoglutarate ® Malate ® Fumarate C. Aconitate ® IsoCitrate ® a-Ketoglutarate ® Fumarate ® Malate ® Oxaloacetate D. Aconitate ® IsoCitrate ® a-Ketoglutarate ® Malate ® Fumarate ® Oxaloacetate E. IsoCitrate ® Aconitate ® a-Ketoglutarate ® Malate ® Oxaloacetate ® Fumarate
C. Aconitate ® IsoCitrate ® a-Ketoglutarate ® Fumarate ® Malate ® Oxaloacetate
In the classical equation for respiration: Glucose + 6O2 --> 6CO2 + 6H2O, the following molecules are found directly in the citric acid cycle: A. O2 B. Glucose and O2 C. CO2 and H2O D. all of these arae found directly in the citric acid cycle
C. CO2 and H2O
Which of the following statements concerning the glyoxylate pathway is FALSE? A. It utilizes one mole of acetyl-CoA per cycle. B. It can produce a net synthesis of 4-carbon fragments that are intermediates of the citric acid cycle. C. It does not occur in the mitochondria. D. It is the main pathway that allows for synthesis of sugars from acetyl-CoA.
C. It does not occur in the mitochondria. [correct] A. It utilizes one mole of acetyl-CoA per cycle. B. It can produce a net synthesis of 4-carbon fragments that are intermediates of the citric acid cycle. D. It is the main pathway that allows for synthesis of sugars from acetyl-CoA.
Which of the following enzymes does not use NAD+ for oxidation? A. Alpha-Ketoglutarate Dehydrogenase complex. B. IsoCitrate Dehydrogenase. C. Succinate Dehydrogenase. D. Malate Dehydrogenase. E. All of these enzymes use NAD+
C. Succinate Dehydrogenase.
Which of the following enzymes is the only membrane-bound enzyme in the citric acid cycle? A. Aconitase. B. IsoCitrate Dehydrogenase. C. Succinate Dehydrogenase. D. Malate Dehydrogenase. E. Alpha-Ketoglutarate Dehydrogenase complex.
C. Succinate Dehydrogenase.
In muscle cells, the following reaction proceeds as written, i.e., from left to right, despite having DG' » +30 kJ/mol. How can this occur? malate + NAD+ ® oxaloacetate + NADH + H+ A. It is obviously thermodynamically favored under standard conditions. B. In the cell, it is kinetically favored, even though it's thermodynamically unfavored. C. The concentration of malate must be higher than oxaloacetate for this reaction to occur in the cell. D. [H+] must be higher in muscle than under standard conditions, thus altering DG' to DG.
C. The concentration of malate must be higher than oxaloacetate for this reaction to occur in the cell.
All but one of the enzymes of the citric acid cycle are found in this part of the mitochondrion: A. The outer membrane. B. The inner membrane. C. The mitochondrial matrix. D. The intermembrane space. E. It is not known where these enzymes are located.
C. The mitochondrial matrix.
A cell in an active metabolic state has A. a high (ATP/ADP) and a high (NADH/NAD+) ratio. B. a high (ATP/ADP) and a low (NADH/NAD+) ratio. C. a low (ATP/ADP) and a low (NADH/NAD+) ratio. D. a low (ATP/ADP) and a high (NADH/NAD+) ratio.
C. a low (ATP/ADP) and a low (NADH/NAD+) ratio.
Which of the following enzymes is not a control point of the citric acid cycle? A. citrate synthase B. isocitrate dehydrogenase C. aconitase D. the a-ketoglutarate dehydrogenase complex
C. aconitase
Which coenzyme listed below is not associated with the a-ketoglutarate dehydrogenase complex? A. thiamine pyrophosphate B. lipoic acid C. biotin D. NAD+
C. biotin
Which of the following is a source of NADPH? A. the pentose phosphate pathway B. a series of reactions in which oxaloacetate is reduced to malate followed by oxidative decarboxylation of the malate to pyruvate C. both of the above D. neither of these
C. both of the above [correct] A. the pentose phosphate pathway B. a series of reactions in which oxaloacetate is reduced to malate followed by oxidative decarboxylation of the malate to pyruvate
The glyoxylate cycle occurs in A. plants and animals. B. bacteria and animals. C. plants and bacteria. D. plants, animals, and bacteria.
C. plants and bacteria.
Which of the following enzymes contains a non-heme iron? A. citrate synthase B. succinyl-CoA synthetase C. succinate dehydrogenase D. fumarase
C. succinate dehydrogenase
Which of the reactions of the citric acid cycle requires FAD as a coenzyme? A. the conversion of isocitrate to a-ketoglutarate B. the conversion of citrate to isocitrate C. the conversion of succinate to fumarate D. the conversion of malate to oxaloacetate
C. the conversion of succinate to fumarate
The reaction in which malate is oxidized to oxaloacetate is not thermodynamically favored. It takes place because A. it is coupled to ATP hydrolysis. B. it involves substrate-level phosphorylation. C. the product is continuously used up in the next reaction of the cycle, which is thermodynamically favored. D. it is coupled to a strong reduction.
C. the product is continuously used up in the next reaction of the cycle, which is thermodynamically favored.
Which group of small molecules best fit the boxes associated with the reaction shown? a b I. ADP + 2 Pi ATP II. NAD+ NADH III. ATP ADP + 2 Pi IV. FAD FADH2 A. I B. II C. III D. IV
D. IV
The conversion of malate to oxaloacetate has a high +DG (it is endergonic). It can take place because: A. It is coupled to hydrolysis of the GTP produce earlier in the cycle. B. It is coupled to hydrolysis of ATP from other sources. C. It involves a substrate level phosphorylation. D. The oxaloacetate product is used up in the subsequent reaction. E. It is coupled to a strong reduction reaction.
D. The oxaloacetate product is used up in the subsequent reaction.
Fluorine is related to the citric acid cycle because: A. fluoroacetyl-CoA is also a substrate for citrate synthase B. fluoroacetate, found in poisonous plants, acts as an inhibitor of aconitase C. fluorocitrate acts as a potent inhibitor of the citric acid cycle D. all of these
D. all of these [correct] A. fluoroacetyl-CoA is also a substrate for citrate synthase B. fluoroacetate, found in poisonous plants, acts as an inhibitor of aconitase C. fluorocitrate acts as a potent inhibitor of the citric acid cycle
Most of the products of the catabolism of sugars, fats and amino acids enter the citric acid cycle as: A. pyruvate B. acetyl-CoA C. malate D. all of these E. none of these
D. all of these [correct] A. pyruvate B. acetyl-CoA C. malate
The enzymes involved in the pyruvate dehydrogenase complex are A. physically separated from each other B. crosslinked to each other by lipoic acid linkers C. covalently bonded to coenzyme A D. associated with each other in a cubical array
D. associated with each other in a cubical array
In the conversion of succinyl-CoA to succinate, GTP is produced from GDP in a reaction in which the source of the added phosphate is A. ATP. B. ADP. C. phosphenolpyruvate. D. inorganic phosphate ion.
D. inorganic phosphate ion.
In the glyoxylate cycle, acetyl-CoA reacts with glyoxylate to produce A. succinyl-CoA B. succinate C. fumarate D. malate
D. malate
Which of the following cannot cross the inner mitochondrial membrane? A. malate B. phosphoenolpyruvate C. succinyl-CoA D. oxaloacetate
D. oxaloacetate
The glyoxylate pathway bypasses part of the citric acid cycle by converting isocitrate to glyoxylate and A. a-ketoglutarate B. fumarate C. succinyl-CoA D. succinate
D. succinate
The reaction of the citric acid cycle that does not take place in the mitochondrial matrix is the one catalyzed by: A. fumarase B. citrate synthase C. isocitrate dehydrogenase D. succinate dehydrogenase E. All of these reactions take place in the matrix
D. succinate dehydrogenase
Which enzyme catalyzes the reaction shown? A. isocitrate dehydrogenase B. malate dehydrogenase C. fumarase D. succinate dehydrogenase
D. succinate dehydrogenase
Which of the following reactions involves substrate-level phosphorylation? A. isocitrate ® a-ketoglutarate B. citrate ® isocitrate C. succinate ® fumarate D. succinyl-CoA ® succinate
D. succinyl-CoA ® succinate
Exhibit 19A The following compounds are all intermediates in the citric acid cycle. Refer to Exhibit 19A. Which intermediate is formed from fumarate? A. 1 B. 2 C. 3 D. 4 E. 5
E. 5
Which of the following vitamins and enzyme cofactors are used by the pyruvate dehydrogenase complex during oxidative decarboxylation? A. Lipoic Acid. B. Niacin. C. Pantothenic Acid. D. Thiamine. E. All of these
E. All of these [correct] A. Lipoic Acid. B. Niacin. C. Pantothenic Acid. D. Thiamine.
Which of the following describes a use for acetyl-CoA as an important intermediate in metabolism? A. Breakdown to CO2 and water, yielding much energy. B. Synthesis of terpenes and steroids. C. Synthesis of oxaloacetate in plants. D. Synthesis of fatty acids. E. All of these are reasons why acetyl-CoA is a central molecule in metabolism.
E. All of these are reasons why acetyl-CoA is a central molecule in metabolism. [correct] A. Breakdown to CO2 and water, yielding much energy. B. Synthesis of terpenes and steroids. C. Synthesis of oxaloacetate in plants. D. Synthesis of fatty acids.
Which of the following statements concerning the citric acid cycle as the central metabolic pathway is true? A. It is involved in the metabolism of sugars and amino acids. B. It is involved in the metabolism of amino acids and lipids. C. It links anaerobic metabolism to aerobic metabolism. D. Many of its intermediates are starting points for synthesis of a variety of compounds. E. All of these are reasons why the citric acid cycle is considered to be the central pathway.
E. All of these are reasons why the citric acid cycle is considered to be the central pathway. [correct] A. It is involved in the metabolism of sugars and amino acids. B. It is involved in the metabolism of amino acids and lipids. C. It links anaerobic metabolism to aerobic metabolism. D. Many of its intermediates are starting points for synthesis of a variety of compounds.
Exhibit 19A The following compounds are all intermediates in the citric acid cycle. Refer to Exhibit 19A. Which intermediate releases CO2 concurrent with oxidation? A. 1 B. 2 C. 3 D. Both 1 and 3 E. Both 2 and 3
E. Both 2 and 3
Which of the following is NOT a component of the pyruvate dehydrogenase complex? A. pyruvate dehydrogenase B. dihydrolipoyl transacetylase C. dihydrolipoyl dehydrogenase D. pyruvate dehydrogenase kinase E. aconitase
E. aconitase [correct] A. pyruvate dehydrogenase B. dihydrolipoyl transacetylase C. dihydrolipoyl dehydrogenase D. pyruvate dehydrogenase kinase
The citric acid cycle begins with the transfer of a two-carbon acetyl group from acetyl-CoA to the four-carbon acceptor compound (oxaloacetate) to form a six-carbon compound (citrate).
True
