Biochemistry 325 Chapter 13

Which of the following is NOT a mechanism for controlling the pyruvate dehydrogenase complex oxidation of pyruvate? Acetyl-CoA competitively inhibits E2 of the complex. The E1 component of the complex is subject to covalent modification that alters its function. NADH competitively inhibits E3 of the complex. Acetyl-CoA competitively inhibits E1 of the complex

Acetyl-CoA competitively inhibits E1 of the complex

Which of the following is NOT a mechanism for controlling the pyruvate dehydrogenase complex oxidation of pyruvate?

Acetyl-CoA competitively inhibits E1 of the complex.

One substrate level phosphorylation occurs in the citric acid cycle in the reaction catalyzed by: α-ketoglutarate dehydrogenase. citrate synthase. succinate dehydrogenase. succinyl CoA synthetase. isocitrate dehydrogenase.

succinyl CoA synthetase.

Which of the following statements about the conversion of acetyl CoA to citrate are true? 1) The reaction is spontaneous. 2) The reaction involves the nucleophilic attack of the enol of acetyl-CoA onto the carbonyl carbon of oxaloacetate. 3) A serine residue hydrolyzes the thioester bond of citroyl-CoA to yield a protein ester intermediate that is subsequently hydrolyzed to citrate. 4) The final product, citrate, has two prochiral substituents.

1) The reaction is spontaneous. 2) The reaction involves the nucleophilic attack of the enol of acetyl-CoA onto the carbonyl carbon of oxaloacetate. that is subsequently hydrolyzed to citrate. 4) The final product, citrate, has two prochiral substituents. NOT: 3) A serine residue hydrolyzes the thioester bond of citroyl-CoA to yield a protein ester intermediate

Which of the following statements about the conversion of acetyl CoA to citrate are true? 1) The reaction is spontaneous. 2) The reaction involves the nucleophilic attack of the enol of acetyl-CoA onto the carbonyl carbon of oxaloacetate. 3) A serine residue hydrolyzes the thioester bond of citroyl-CoA to yield a protein ester intermediate that is subsequently hydrolyzed to citrate. 4) The final product, citrate, has two prochiral substituents.

1) The reaction is spontaneous. 2) The reaction involves the nucleophilic attack of the enol of acetyl-CoA onto the carbonyl carbon of oxaloacetate. 3) A serine residue hydrolyzes the thioester bond of citroyl-CoA to yield a protein ester intermediate that is subsequently hydrolyzed to citrate.

Outline the mechanism of the conversion of α-ketoglutarate to succinyl-CoA catalyzed by α-ketoglutarate dehydrogenase complex.

1. Decarboxylation 2. Oxidation of 4-carbon group, reduction of lipoamide disulfide 3. Transacylation 4. Dihydrolipoyl dehydrogenase activity 5. Enzymatic FADH2 reoxyation by NAD+

In the citric acid cycle as well as in other processes, the human body takes advantage of the reactivity of thioesters. Which of the following statements about thioesters is NOT true? 1. The thioester has extensive π overlap between the S and carbonyl carbon. 2. The thioester bond is destabilized. 3. There is little double bond character to the C-SR bond. 4. The thioester bond is a weaker bond, making RS- a good leaving group.

1. The thioester has extensive π overlap between the S and carbonyl carbon.

Suppose that aconitase did not bind its substrate asymmetrically. What fraction of the carbon atoms introduced in one cycle as acetyl-CoA would be released in the first turn of the cycle? What fraction of the carbon atoms that entered in the first cycle would be released in the second turn?

1/4 3/8

How many μ moles of acetaldehyde are required to allow complete oxidation of the pyruvate to 15μ moles of CO2? (Do not take into account the concentration that is already in the system.

10 micro moles

Arrange the sequence of events for the conversion of succinyl-CoA to succinate and ATP (or GTP) in the correct order: 1) The phosphate group is transferred from a histidine residue of the phosphorylated enzyme intermediate to the nucleotide. 2) Inorganic phosphate reacts at the thioester of succinyl-CoA to yield a mixed phosphoanhydride. 3) A His residue from the protein is phosphorylated by succinyl phosphate.

2) Inorganic phosphate reacts at the thioester of succinyl-CoA to yield a mixed phosphoanhydride 1) The phosphate group is transferred from a histidine residue of the phosphorylated enzyme intermediate to the nucleotide.. 3) A His residue from the protein is phosphorylated by succinyl phosphate.

Which of the following citric acid intermediates is(are) not used in the preparation of the products shown? 1) citrate ⟶ fatty acids, steroids 2) alpha-ketoglutarate ⟶ steroids 3) oxaloacetate ⟶ purines, pyrimidines 4) alpha-ketoglutarate ⟶ heme

2) alpha-ketoglutarate ⟶ steroids 4) alpha-ketoglutarate ⟶ heme

Write a balanced equation for the conversion in the glyoxylate cycle of two acetyl units, as acetyl-CoA, to oxaloacetate. 2acetyl−CoA+2NAD++E−FADH2+2H2O→oxaloacetate+2NADH+E−FAD+2CoA−SH+2H+ 2acetyl−CoA+NAD++2H2O→oxaloacetate+NADH+2CoA−SH+H+ 2acetyl−CoA+2NADH+E−FAD+2H2O→oxaloacetate+2NAD++E−FADH2+2CoA−SH 2acetyl−CoA+2NAD++E−FAD+3H2O→oxaloacetate+2NADH+E−FADH2+2CoA−SH+2H+

2acetyl−CoA+2NAD++E−FAD+3H2O→oxaloacetate+2NADH+E−FADH2+2CoA−SH+2H+

The conversion of 2 moles of oxaloacetate to glucose. 2oxaloacetate+2NADH+2H++2H2O→glucose+2CO2+2NAD+ 2oxaloacetate+2NAD++2H2O→glucose+2CO2+2NADH+2H+ 2oxaloacetate+2ATP+2GTP+2NADH+2H++4H2O→glucose+2CO2+2NAD++2ADP+2GDP+4Pi 2oxaloacetate+2ATP+2GTP+2NAD++4H2O→glucose+2CO2+2NADH+2H++2ADP+2GDP+4Pi

2oxaloacetate+2ATP+2GTP+2NADH+2H++4H2O→glucose+2CO2+2NAD++2ADP+2GDP+4Pi

In converting 1 mole of glucose to lactate a total of _____ ATP equivalents are _____

3, generated

Which of the following is NOT one of the three stages of respiration? 1. electron transport and oxidative phosphorylation 2. the conversion of pyruvate to acetyl-CoA 3. the synthesis of pyruvate 4. the oxidation of acetyl-CoA to two molecules of CO2

3. the synthesis of pyruvate

Calculate the ATP yield per mole of sucrose metabolized by anaerobic glycolysis starting with hydrolytic cleavage.

4 mol

Arrange the sequence of reactions that occur in the conversion of pyruvate to acetyl-CoA in the correct order: 1) The anion of the hydroxyethyl group attacks one sulfur of the disulfide in lipoic acid, and the resulting intermediate is oxidized to an acetyl thioester. 2) FAD is reduced to FADH2, while the two thiols of reduced lipoic acid are reoxidized back to a disulfide. 3) FADH2 is oxidized by NAD+. 4) Thiamine pyrophosphate decarboxylates pyruvate to yield hydroxyethyl-TPP. 5) The thioester derived from lipoic acid transfers its acetyl group to CoA.

4) Thiamine pyrophosphate decarboxylates pyruvate to yield hydroxyethyl-TPP. 1) The anion of the hydroxyethyl group attacks one sulfur of the disulfide in lipoic acid, and the resulting intermediate is oxidized to an acetyl thioester. 5) The thioester derived from lipoic acid transfers its acetyl group to CoA. 2) FAD is reduced to FADH2, while the two thiols of reduced lipoic acid are reoxidized back to a disulfide. 3) FADH2 is oxidized by NAD+.

Arrange the sequence of reactions that occur in the conversion of pyruvate to acetyl-CoA in the correct order: 1) The anion of the hydroxyethyl group attacks one sulfur of the disulfide in lipoic acid, and the resulting intermediate is oxidized to an acetyl thioester. 2) FAD is reduced to FADH2, while the two thiols of reduced lipoic acid are reoxidized back to a disulfide. 3) FADH2 is oxidized by NAD+. 4) Thiamine pyrophosphate decarboxylates pyruvate to yield hydroxyethyl-TPP. 5) The thioester derived from lipoic acid transfers its acetyl group to CoA.

4) Thiamine pyrophosphate decarboxylates pyruvate to yield hydroxyethyl-TPP. 1) The anion of the hydroxyethyl group attacks one sulfur of the disulfide in lipoic acid, and the resulting intermediate is oxidized to an acetyl thioester. 5) The thioester derived from lipoic acid transfers its acetyl group to CoA 2) FAD is reduced to FADH2, while the two thiols of reduced lipoic acid are reoxidized back to a disulfide. 3) FADH2 is oxidized by NAD+.

Calculate the ATP yield per mole of sucrose metabolized by anaerobic glycolysis starting with phosphorlytic cleavage.

5 mol

In converting 2 moles of lactate to glucose a total of______ ATP equivalents are _____

6 consumed

Taking one mole of glucose through glycolysis and the citric acid cycle generates: 6C02, 8 NADH/H+, 1FADH2 and 1 ATP. 6C02, 8 NADH/H+, 2FADH2 and 4 ATP. 6C02, 8 NADH/H+, 1FADH2 and 2 ATP. 6C02, 10 NADH/H+, 2FADH2 and 4 ATP. 6C02, 10 NADH/H+, 2FADH2 and 2 ATP.

6C02, 10 NADH/H+, 2FADH2 and 4 ATP.

Which of the following coenzymes participate in the reactions of the pyruvate dehydrogenase complex? 1) thiamine pyrophosphate 2) lipoic acid 3) FAD 4) NAD+ 5) CoA

ALL

Which of the following statements about regulation of phosphofructokinase is FALSE? Fructose 2,6-bisphosphate is an activator. ADP is an activator. ATP decreases the apparent Km for fructose-6-phosphate. AMP is an activator. Citrate is an inhibitor.

ATP decreases the apparent Km for fructose-6-phosphate.

Considering the evidence that led Krebs to propose a cyclic pathway for oxidation of pyruvate, discuss the type of experimental evidence that might have led to realization of the cyclic nature of the glyoxylate pathway. Addition to isolated glyoxysomes of isocitrate, glyoxylate, malate, or oxaloacetate would inhibit succinate formation out of proportion and increase the concentrations of other components of glyoxylate pathway. Addition to isolated glyoxysomes of succinate would stimulate citrate, isocitrate, glyoxylate, malate, and oxaloacetate formation out of proportion to the amount added. Addition to isolated glyoxysomes of citrate, isocitrate, glyoxylate, malate, or oxaloacetate would stimulate succinate formation out of proportion to the amount added. Addition to isolated glyoxysomes of isocitrate lyase inhibitors would decrease the concentrations of all components of glyoxylate pathway.

Addition to isolated glyoxysomes of citrate, isocitrate, glyoxylate, malate, or oxaloacetate would stimulate succinate formation out of proportion to the amount added.

Which of the following coenzymes participate in the reactions of the pyruvate dehydrogenase complex? 1) thiamine pyrophosphate 2) lipoic acid 3) FAD 4) NAD+ 5) CoA

All

Arrange the sequence of events for the conversion of succinyl-CoA to succinate and ATP (or GTP) in the correct order: 1) The phosphate group is transferred from a histidine residue of the phosphorylated enzyme intermediate to the nucleotide. 2) Inorganic phosphate reacts at the thioester of succinyl-CoA to yield a mixed phosphoanhydride. 3) A His residue from the protein is phosphorylated by succinyl phosphate.

Arrange the sequence of events for the conversion of succinyl-CoA to succinate and ATP (or GTP) in the correct order: 2) Inorganic phosphate reacts at the thioester of succinyl-CoA to yield a mixed phosphoanhydride. 3) A His residue from the protein is phosphorylated by succinyl phosphate. 1) The phosphate group is transferred from a histidine residue of the phosphorylated enzyme intermediate to the nucleotide.

Why? FBP has the greatest thermodynamic stability among the other substances involved in glycolysis. The formation of FBP is the most exergonic step in the whole glycolysis process. Since FBP is not involved in any other metabolic process, this leads to its rapid accumulation. As triose phosphate began to accumulate, the reverse reaction may drive both DHAP and GAP back to FBP.

As triose phosphate began to accumulate, the reverse reaction may drive both DHAP and GAP back to FBP.

Why does it make good metabolic sense for phosphoenolpyruvate carboxykinase, rather than pyruvate carboxylase, to be the primary target for the regulation of gluconeogenesis at the level of control of enzyme synthesis? Because in different conditions pyruvate carboxylase can either catalyzes the first reaction committed to gluconeogenesis or inhibit the process, whereas PEPCK catalyzes the first reaction at any conditions. Because pyruvate carboxylase has two metabolic roles: replenishment of citric acid cycle intermediates and initiation of gluconeogenesis. PEPCK catalyzes the first reaction committed to gluconeogenesis. Because the process of regulation of gluconeogenesis at the level of control of enzyme synthesis by pyruvate carboxylase has much higher energy barrier for activation than in case of PEPCK. Because the concentration of pyruvate carboxylase is low. If it is a the primary target for the regulation of gluconeogenesis the lack of pyruvate carboxylase would cause CO2 deactivation which affects the photosynthesis.

Because pyruvate carboxylase has two metabolic roles: replenishment of citric acid cycle intermediates and initiation of gluconeogenesis. PEPCK catalyzes the first reaction committed to gluconeogenesis.

Consider the fate of pyruvate labeled with 14C in each of the following positions: carbon 1 (carboxyl), carbon 2 (carbonyl), and carbon 3 (methyl). Predict the fate of each labeled carbon during one turn of the citric acid cycle. C-1 and C-2 all released as CO2. C-3: retained in oxaloacetate. C-1 retained in oxaloacetate. C-2 and C-3: all released as CO2. C-1 released as CO2. C-2 and C-3: all retained in oxaloacetate. C-1 and C-2 all retained in oxaloacetate. C-3: released as CO2.

C-1 released as CO2. C-2 and C-3: all retained in oxaloacetate.

activation of pyruvate dehydrogenase phosphatase by Ca2+ Ca2+ interacts with active sites of four proteins which participate in contraction of vertebrate muscle, which places a huge demand on ATP production. Ca2+ is a critical signaling molecule for contraction in vertebrate muscle, which places a huge demand on ATP production. Ca2+ activates PDH through interaction with an active site of enzyme, when huge amount of ATP molecules is needed for protein synthesis activation. Ca2+ mediates stimulation of PDH activity during muscle contraction, which can produce a huge amound of ATP molecules.

Ca2+ is a critical signaling molecule for contraction in vertebrate muscle, which places a huge demand on ATP production.

During acetyl CoA formation and the citric acid cycle, all of the carbon atoms that enter cellular respiration in the glucose molecule are released in the form of CO2. Use this diagram to track the carbon-containing compounds that play a role in these two stages.

Citrate (6) Isocitrate (6) Alpha Ketoglutarate (5) Succinyl CoA (4) Succinate (4) Malate (4) Oxaloacetate (4)

Put the enzymes of the citric acid cycle in order from left to right.

Citrate Synthase Aconitase isocitrate dehydrogenase alpha ketoglutarate dehydrogenase Succinyl CoA synthetase Succinate dehydrogenase fumarase malate dehydrogenase

Which of the following does NOT regulate flux through the citric acid cycle? Ca2+ activation of isocitrate dehydrogenase Allosteric inhibition of isocitrate dehydrogenase by ADP Concentration of intermediates Inhibition of α-ketoglutarate dehydrogenase by succinyl CoA The ratio of [NAD+]/[NADH]

Concentration of intermediates

Which of the following does NOT apply to the reaction catalyzed by the pyruvate dehydrogenase complex? It takes place in the mitochondrion. The process is highly exergonic and essentially irreversible in vivo. Each intermediate in the five step reaction is able to diffuse to the next active site in a sequential manner. The product is acetyl CoenzymeA. It is an oxidative decarboxylation.

Each intermediate in the five step reaction is able to diffuse to the next active site in a sequential manner.

Part B Part complete Show any coenzymes that might be involved. Check all that apply. ADP+Pi CoA−SH E−FAD Coenzyme Q NAD+ PPi TPP

E−FAD NAD+

All of the reactions of both glycolysis and gluconeogenesis occur in the cytosol. True False

False

Liver pyruvate kinase is activated by dephosphorylation in response to glucagon. True False

False

The two carbon atoms that are lost as CO2 in the third and fourth steps of the citric acid cycle are the same as the two carbon atoms of acetyl CoA because of the stereochemistry of the isocitrate dehydrogenase reaction. True False

False

Which of the following is NOT involved in glycogen synthesis? UDP-glucose Glycogenin Amylo-(1,4 to 1,6)-transglycosylase Glycogen phosphorylase Glycogen synthase

Glycogen phosphorylase

Explain why glucose consumption must increase in hypoxic tissues to provide the same amount of ATP that could be produced from glucose in normoxic (normal O2 levels) tissues. In hypoxic tissues, only by the citric acid cycle is responsible for ATP production, whereas in normoxic tissues both glycolysis and oxidative phosphorylation are involved. In hypoxic tissues, in contrast to normoxic tissues, ATP is additionally consumed to transform lactate to pyruvate. In hypoxic tissues, ATP is produced only by glycolysis, whereas in normoxic tissues, the citric acid cycle + oxidative phosphorylation can be used. Oxygen is the limiting reactant in ATP producing, so ATP is produced in hypoxic tissues more slowly than in normoxic tissues.

In hypoxic tissues, ATP is produced only by glycolysis, whereas in normoxic tissues, the citric acid cycle + oxidative phosphorylation can be used.

In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction.

It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA

Which of the following cannot be metabolized to make molecules that can enter the citric acid cycle?

Metal Ions

How would increasing PDK expression decrease the rate of mitochondrial respiration? PDK activity requires a huge consumption of ATP molecules. ATP are formed easily by glycolysis in hypoxic tissues, so processes of mitochondrial respiration are deprived. PDK increases the conversion of pyruvate to lactate in the mitochondria, decreasing NADH production. Thus, the rate of mitochondrial respiration is decreased. PDK phosphorylates the E1 subunit of PDH complex, decreasing flux through citric acid cycle. Thus, NADH production and respiration is decreased.

PDK phosphorylates the E1 subunit of PDH complex, decreasing flux through citric acid cycle. Thus, NADH production and respiration is decreased.

Predict which one of the five steps of the α-ketoglutarate dehydrogenase complex reaction is metabolically irreversible under physiological conditions. Step 1. Decarboxylation. Step 2. Oxidation of 4-carbon group, reduction of lipoamide disulfide. Step 3. Transacylation. Step 4. Dihydrolipoyl dehydrogenase. Step 5. FADH2 enzymatically reoxidized by NAD+ to form NADH.

Step 1. Decarboxylation.

Which of the following enzymes catalyzes a reaction of the citric acid cycle that does NOT produce reduced electron carriers? Succinate dehydrogenase α-ketoglutarate dehydrogenase Malate dehydrogenase Isocitrate dehydrogenase Succinyl CoA synthetase

Succinyl CoA synthetase

Which of the following techniques can be used to quantify protein-protein interactions? Surface plasmon resonance Chemical cross-linking The two-hybrid system Co-immunoprecipitation Affinity chromatography

Surface plasmon resonance

Explain why. The CO2 product diffuses away from the enzyme, and does not rebind to any significant extent. There is too high level of CO2 partial pressure in an organism, it does not allow CO2 to participate in reverse reaction. The CO2 product increases the pH on rreaction area, than inhibits the reverse reaction. The CO2 product is immediately consumed in the reaction of pyruvare formation from acetate.

The CO2 product diffuses away from the enzyme, and does not rebind to any significant extent.

Consider glucose biosynthesis from each of the following substrates and predict which of these pathways would be inhibited by avidin. Check all that apply. fructose-6-phosphate malate phosphoenolpyruvate oxaloacetate lactate

lactate

How would increasing LDH expression increase the rate of glycolysis? The LDH reaction ensures a continuous supply of oxidized NAD+ to allow glycolysis to operate at an increased rate. The LDH activity increases the ratio NADH/NAD+ to allow glycolysis to operate at an increased rate. The LDH reaction produces supplementary amounts of reduced NADH to allow glycolysis to operate at an increased rate. The LDH activity increases the level of lactate in tissues to allow glycolysis to operate at an increased rate.

The LDH reaction ensures a continuous supply of oxidized NAD+ to allow glycolysis to operate at an increased rate.

[methyl-14C]Pyruvate was administered to isolated liver cells in the presence of sufficient malonate to block succinate dehydrogenase completely. After a time, isocitrate was isolated and found to contain label in both carbon 2 and carbon 4: When this reaction occurs in isolated liver cells, specific mechanism is activated. As the result, oxaloacetate is converted to isocitrate directly, so C-2 and C-4 carbons of isocitrate are labeled. The action of pyruvate carboxylase on the labeled pyruvate yields oxaloacetate labeled such that, when these carbons proceed through the citric acid cycle, so C-4 of isocitrate is labeled in addition. Succinate dehydrogenase is blocked completely, so citrate will be formed straight from two molecules of [methyl-14C]-labeled pyruvate througth the reaction of aldol condensation.

The action of pyruvate carboxylase on the labeled pyruvate yields oxaloacetate labeled such that, when these carbons proceed through the citric acid cycle, so C-4 of isocitrate is labeled in addition.

How do you explain this result? The addition of alcohol dehydrogenase plus its substrate allows regeneration of NAD+. Now oxidized NAD+ is available for the additional TCA reactions in which additional CO2 can be produced. The addition of alcohol dehydrogenase plus its substrate allows regeneration of GDP. Now oxidized GDP is available for the additional phosphorylation in which additional CO2 can be produced. The addition of alcohol dehydrogenase plus its substrate allows regeneration of FAD. Now oxidized FAD is available for the additional TCA reactions in which additional CO2 can be produced. The addition of alcohol dehydrogenase plus its substrate allows regeneration of oxaloacetate. Additional amount of the substrate is available for the following TCA reactions in which additional CO2 can be produced.

The addition of alcohol dehydrogenase plus its substrate allows regeneration of NAD+. Now oxidized NAD+ is available for the additional TCA reactions in which additional CO2 can be produced.

Assume you have a solution containing the pyruvate dehydrogenase complex and all the enzymes of the TCA cycle, but none of the metabolic intermediates. When you supplement this solution with 5μ moles each of pyruvate, oxaloacetate, coenzyme A, NAD+, FAD, GDP, and Pi, you find that 5μ moles of CO2 are evolved and then the reaction stops. When you add alcohol dehydrogenase and its substrate acetaldehyde, additional CO2 is produced. How many μ moles of acetaldehyde are required to allow complete oxidation of the pyruvate to 15μ moles of CO2? (Do not take into account the concentration that is already in the system.)

The addition of alcohol dehydrogenase plus its substrate allows regeneration of NAD+. Now oxidized NAD+ is available for the additional TCA reactions in which additional CO2 can be produced. 10 μmol

Individual with a glucose-6-phosphatase deficiency suffers from chronic hypoglycemia. The glucose-6-phosphatase deficiency would interfere with release of glucose from the liver for export to other tissues. The glucose-6-phosphatase is the catalyst for glucose manufacturing reactions. The glucose-6-phosphatase deficiency would interfere with production of ATP, and so there would be lack of glucose. The glucose-6-phosphatase deficiency would allow all of the glucose to participate in citric acid cycle.

The glucose-6-phosphatase deficiency would interfere with release of glucose from the liver for export to other tissues.

Only gluconeogenic tissues contain appreciable levels of glucose-6-phosphatase. The glucose-6-phosphatase controls the level of production ATP that is necessary for glycolysis in gluconeogenic tissues. The glucose-6-phosphatase is produced in gluconeogenic tissues, and then small amounts of glucose-6-phosphatase are delivered to other tissues. The glucose-6-phosphatase can inhibit production of citric acid cycle intermediates. The gluconeogenic tissues absorb excess amounts of glucose-6-phosphatase to prevent the inhibition. The glucose-6-phosphatase plays a role only in primarily liver because its function is to manufacture glucose for export.

The glucose-6-phosphatase plays a role only in primarily liver because its function is to manufacture glucose for export.

Given the roles of NAD+/NADH in dehydrogenation reactions and NADPH/NADP+ in reductions, would you expect the intracellular ratio of NAD+/NADH to be high or low? The intracellular ratio of NAD+/NADH should be high. The intracellular ratio of NAD+/NADH should be low.

The intracellular ratio of NAD+/NADH should be high.

Based on your answer in part A, how does this pathway compare to the standard citric acid cycle in energy yield? The modified pathway generates one less NADH+H+ than the standard pathway. There is no difference in the number of ATP generated. The modified pathway generates one more ATP than the standard pathway. There is no difference in the number of reduced cofactors generated. The modified pathway generates one more NADH+H+ than the standard pathway. There is no difference in the number of ATP generated. The modified pathway generates one less ATP than the standard pathway. There is no difference in the number of reduced cofactors generated. There is no difference in energy yield between two pathways.

The modified pathway generates one less ATP than the standard pathway. There is no difference in the number of reduced cofactors generated.

In the citric acid cycle as well as in other processes, the human body takes advantage of the reactivity of thioesters. Which of the following statements about thioesters is NOT true? 1. The thioester has extensive π overlap between the S and carbonyl carbon. 2. The thioester bond is destabilized. 3. There is little double bond character to the C-SR bond. 4. The thioester bond is a weaker bond, making RS- a good leaving group.

The thioester has extensive π overlap between the S and carbonyl carbon.

Choose correctly all products and coenzymes.

Thiamine pyrophosphate - 4 C TPP derivative of a alpha ketoglutarate lipoamide disulfide - dihydrolipoamide succinate Coenzyme A - Succinate CoA FAD - FADH2 NAD - NADH

Fluoroacetate functions as a poison by what mechanism?

This compound is first converted to 2-fluorocitrate, which subsequently inhibits aconitase.

activation of pyruvate carboxylase by acetyl-CoA This is a signal that pyruvate can be shunted into gluconeogenesis instead of being oxidized in the citric acid cycle. In addition, it is a signal of unbalanced fat and carbohydrate metabolism. This is a signal that part of available pyruvate can be metabolized into oxaloacetate, when the energy charge is low and production of additional ATP through the citric acid cycle is required. This is a signal that pyruvate can be oxidized in the citric acid cycle instead of shunted into gluconeogenesis. In addition, it is a signal of activation carbohydrate metabolism. This is a signal that pyruvate can be oxidized in the citric acid cycle as well as can be shunted into gluconeogenesis. In addition, it is a signal of activation fat metabolism.

This is a signal that pyruvate can be shunted into gluconeogenesis instead of being oxidized in the citric acid cycle. In addition, it is a signal of unbalanced fat and carbohydrate metabolism.

inhibition of isocitrate dehydrogenase by NADH This is a signal to reduce flux through the citric acid cycle when metabolism of acetyl-CoA through glyoxylate pathway is more preferred. This is a signal to reduce flux through the citric acid cycle when additional amount of acetyl-CoA is needed for lipid biosynthesis. This is a signal to reduce flux through the citric acid cycle when levels of reduced electron carriers are adequate for energy generation. This is a signal to increase flux through the citric acid cycle when metabolism of acetyl-CoA through glyoxylate pathway is less preferred.

This is a signal to reduce flux through the citric acid cycle when levels of reduced electron carriers are adequate for energy generation.

activation of pyruvate dehydrogenase kinase by NADH This tends to activate pyruvate dehydrogenase when level of NADH is sufficient for ATP production via the respiratory chain and, hence, to make pyruvate unavailable for other purposes. This tends to activate pyruvate dehydrogenase when level of NADH is sufficient for ATP production via the cytric acid cycle and, hence, to increase the oxidation of the lipids and carbonhydrates. This tends to inactivate pyruvate dehydrogenase and to activate pyruvate carboxylase and to increase the oxaloacetate production and, hence, to activate gluconeogenesis. This tends to inactivate pyruvate dehydrogenase when level of NADH is sufficient for ATP production via the respiratory chain and, hence, to make pyruvate available for other purposes.

This tends to inactivate pyruvate dehydrogenase when level of NADH is sufficient for ATP production via the respiratory chain and, hence, to make pyruvate available for other purposes.

Aconitase catalyzes the reaction: citrate⇌isocitrate The standard free energy change, ΔG∘', for this reaction is +6.3 kJ/mol. However, the observed free energy change (ΔG) for this reaction in mammalian mitochondria at 25 ∘C is ~ 0 kJ/mol. Calculate the ratio of [isocitrate]/[citrate] in mitochondria. Is this reaction likely to be a control point for the citric acid cycle? Why or why not?

[isocitrate][citrate] = 7.9×10−2 No, because aconitase catalyzes a freely reversible reaction.

All of the enzymes of the citric acid cycle are located in the mitochondrion. True False

True

NAD+, coenzyme A, thiamine pyrophosphate, lipoic acid and FAD are all cofactors used in the reaction catalyzed by pyruvate dehydrogenase.

True

Transamination reactions can be used to provide intermediates for the citric acid cycle. True False

TrueFw

activation of isocitrate dehydrogenase by ADP When the energy charge is low, the accumulation of ADP provides a signal to activate the citric acid cycle and thereby increase the oxidation of nutrients for ATP production. When the energy charge is high, the accumulation of ADP provides a signal to activate the citric acid cycle and thereby increase the succinate production for electron transport chain. The accumulation of ADP provides a signal to activate the isocitrate dehydrogenase and thereby increase \alpha-ketoglutarate level in organism preventing ATP consumption in the process of glutamine desamination. When the energy charge is high, the accumulation of ADP provides a signal to activate the citric acid cycle and thereby increase the oxidation of nutrients for proteins production.

When the energy charge is low, the accumulation of ADP provides a signal to activate the citric acid cycle and thereby increase the oxidation of nutrients for ATP production

Succinate semialdehyde is then converted to succinate, which is further metabolized by standard citric acid cycle enzymes. What kind of reaction is required to convert succinate semialdehyde to succinate? a decarboxylation reaction an oxidation reaction an enolization reaction a reduction reaction a hydratation reaction

an oxidation reaction

The reaction catalyzed by PFK−2. α−D−glucose+Mg2+⋅ATP→α−D−glucose−6−phosphate+ADP+H+ fructose−6−phosphate+ATP→fructose−2,6−bisphosphate+ADP α−D−glucose+Mg2+⋅ADP→α−D−glucose−6−phosphate+ATP+H+ fructose−6−phosphate+ADP→fructose−2,6−bisphosphate+ATP

fructose−6−phosphate+ATP→fructose−2,6−bisphosphate+ADP

xaloacetate is replenished via the ________ in plants and bacteria.

glyoxylate pathway

The mechanism for the conversion of α-ketoglutarate to succinyl-CoA resembles the mechanism of which of the following enzymes?

pyruvate dehydrogenase complex

Given what you know about the function of the glyoxylate cycle and the regulation of the citric acid cycle, propose control mechanisms that might regulate the glyoxylate cycle. Check all that apply. increasing fatty acids level in a cell increasing the availability of glucose as the carbon source substrate-level control of succinyl-CoA synthetase substrate-level control of citrate synthase activation of succinic dehydrogenase

substrate-level control of succinyl-CoA synthetase inhibition of isocitrate lyase by succinate activation of citrate lyase by acetyl-CoA or fatty acids

In the citric acid cycle, ATP molecules are produced by _____

substrate-level phosphorylation

The glyoxylate cycle in plants and bacteria can be used for net carbohydrate synthesis from fat because isocitrate lyase yields glyoxylate and ________ without the loss of two carbons as occurs in the citric acid cycle.

succinate