Question 1

Preparation of an extract of muscle results in a dramatic decrease in the concentration of citric acid cycle intermediates compared to their concentrations in the tissue.However,in 1935,Szent-Gyorgi showed that the production of CO₂ by the extract increased when succinate was added.In fact,for every mole of succinate added,many extra moles of CO₂ were produced.Explain this effect in terms of the known catabolic pathways.

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Question 2

The citric acid cycle is frequently described as the major pathway of aerobic catabolism,which means that it is an oxygen-dependent degradative process.However,none of the reactions of the cycle directly involves oxygen as a reactant.Why is the pathway oxygen-dependent?

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Question 3

Show the steps of the citric acid cycle in which a six-carbon compound is converted into the first four-carbon intermediate in the path.For each step,show structures of substrate and product,name the enzyme responsible,and show where cofactors participate.

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Question 4

Explain in quantitative terms the circumstances under which the following reaction can proceed. L-Malate + NAD⁺$\rightarrow$ oxaloacetate + NADH + H⁺ $\Delta$G'° = +29.7 kJ/mol

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Question 5

There are few,if any,humans with defects in the enzymes of the citric acid cycle.Explain this observation in terms of the role of the citric acid cycle.

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Question 6

Show the structures of the reactants and products for two of the four redox reactions in the citric acid cycle.Indicate where any cofactors participate,and label the reactants,products,and cofactors as oxidants or reductants in the reaction.

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Question 7

Explain why fluorocitrate,a potent inhibitor of the enzyme aconitase,is a deadly poison.

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Question 8

You are in charge of genetically engineering a new bacterium that will derive all of its ATP from sunlight by photosynthesis.Will you put the enzymes of the citric acid cycle in this organism? Briefly explain why or why not.

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Question 9

Show the three reactions in the citric acid cycle in which NADH is produced,including the structures.None of these reactions involves molecular oxygen (O₂),but all three reactions are strongly inhibited by anaerobic conditions;explain why.

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Question 10

Show the reactions by which $\alpha$-ketoglutarate is converted to malate in the citric acid cycle.

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Question 11

The human disease beriberi is caused by a deficiency of thiamine in the diet.People with severe beriberi have higher than normal levels of pyruvate in their blood and urine.Explain this observation in terms of specific enzymatic reaction(s).

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Question 12

Draw the citric acid cycle from isocitrate to fumarate only,showing and naming each intermediate.Show where high-energy phosphate compounds or reduced electron carriers are produced or consumed,and name the enzyme that catalyzes each step.

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Question 13

In the citric acid cycle,a five-carbon compound is decarboxylated to yield an activated four-carbon compound.Show the substrate and product in this step,and indicate where any cofactor(s)participate(s).

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Question 14

Match the cofactor with its function in the citric acid cycle.A given function may be used more than once or not at all.
-

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Question 15

In which reaction of the citric acid cycle does substrate-level phosphorylation occur?

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Question 16

At what point in the citric acid cycle do the methyl carbon from acetyl-CoA and the carbonyl carbon from oxaloacetate become chemically equivalent?

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Question 17

Show the steps of the citric acid cycle from succinyl-CoA to oxaloacetate only.For each step,show structures of substrate and product,name the enzyme responsible,and show where cofactors participate.

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Question 18

Germinating plant seeds can convert stored fatty acids into oxaloacetate and a variety of carbohydrates.Animals cannot synthesize significant quantities of oxaloacetate or glucose from fatty acids.What accounts for this difference?

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Quiz 16: The Citric Acid Cycle

The citric acid cycle is frequently described as the major pathway of aerobic catabolism,which means that it is an oxygen-dependent degradative process.However,none of the reactions of the cycle directly involves oxygen as a reactant.Why is the pathway oxygen-dependent?

Show the steps of the citric acid cycle in which a six-carbon compound is converted into the first four-carbon intermediate in the path.For each step,show structures of substrate and product,name the enzyme responsible,and show where cofactors participate.

Explain in quantitative terms the circumstances under which the following reaction can proceed. L-Malate + NAD⁺ $\rightarrow$ oxaloacetate + NADH + H⁺ $\Delta$ G'° = +29.7 kJ/mol

There are few,if any,humans with defects in the enzymes of the citric acid cycle.Explain this observation in terms of the role of the citric acid cycle.

Show the structures of the reactants and products for two of the four redox reactions in the citric acid cycle.Indicate where any cofactors participate,and label the reactants,products,and cofactors as oxidants or reductants in the reaction.

Explain why fluorocitrate,a potent inhibitor of the enzyme aconitase,is a deadly poison.

You are in charge of genetically engineering a new bacterium that will derive all of its ATP from sunlight by photosynthesis.Will you put the enzymes of the citric acid cycle in this organism? Briefly explain why or why not.

Show the three reactions in the citric acid cycle in which NADH is produced,including the structures.None of these reactions involves molecular oxygen (O₂),but all three reactions are strongly inhibited by anaerobic conditions;explain why.

Show the reactions by which $\alpha$ -ketoglutarate is converted to malate in the citric acid cycle.

The human disease beriberi is caused by a deficiency of thiamine in the diet.People with severe beriberi have higher than normal levels of pyruvate in their blood and urine.Explain this observation in terms of specific enzymatic reaction(s).

Draw the citric acid cycle from isocitrate to fumarate only,showing and naming each intermediate.Show where high-energy phosphate compounds or reduced electron carriers are produced or consumed,and name the enzyme that catalyzes each step.

In the citric acid cycle,a five-carbon compound is decarboxylated to yield an activated four-carbon compound.Show the substrate and product in this step,and indicate where any cofactor(s)participate(s).

Match the cofactor with its function in the citric acid cycle.A given function may be used more than once or not at all. -

In which reaction of the citric acid cycle does substrate-level phosphorylation occur?

At what point in the citric acid cycle do the methyl carbon from acetyl-CoA and the carbonyl carbon from oxaloacetate become chemically equivalent?

Show the steps of the citric acid cycle from succinyl-CoA to oxaloacetate only.For each step,show structures of substrate and product,name the enzyme responsible,and show where cofactors participate.

Germinating plant seeds can convert stored fatty acids into oxaloacetate and a variety of carbohydrates.Animals cannot synthesize significant quantities of oxaloacetate or glucose from fatty acids.What accounts for this difference?

Quiz 16: The Citric Acid Cycle

The citric acid cycle is frequently described as the major pathway of aerobic catabolism,which means that it is an oxygen-dependent degradative process.However,none of the reactions of the cycle directly involves oxygen as a reactant.Why is the pathway oxygen-dependent?

Show the steps of the citric acid cycle in which a six-carbon compound is converted into the first four-carbon intermediate in the path.For each step,show structures of substrate and product,name the enzyme responsible,and show where cofactors participate.

Explain in quantitative terms the circumstances under which the following reaction can proceed. L-Malate + NAD+ →\rightarrow→ oxaloacetate + NADH + H+ Δ\DeltaΔ G'° = +29.7 kJ/mol

There are few,if any,humans with defects in the enzymes of the citric acid cycle.Explain this observation in terms of the role of the citric acid cycle.

Show the structures of the reactants and products for two of the four redox reactions in the citric acid cycle.Indicate where any cofactors participate,and label the reactants,products,and cofactors as oxidants or reductants in the reaction.

Explain why fluorocitrate,a potent inhibitor of the enzyme aconitase,is a deadly poison.

You are in charge of genetically engineering a new bacterium that will derive all of its ATP from sunlight by photosynthesis.Will you put the enzymes of the citric acid cycle in this organism? Briefly explain why or why not.

Show the three reactions in the citric acid cycle in which NADH is produced,including the structures.None of these reactions involves molecular oxygen (O2),but all three reactions are strongly inhibited by anaerobic conditions;explain why.

Show the reactions by which α\alphaα -ketoglutarate is converted to malate in the citric acid cycle.

The human disease beriberi is caused by a deficiency of thiamine in the diet.People with severe beriberi have higher than normal levels of pyruvate in their blood and urine.Explain this observation in terms of specific enzymatic reaction(s).

Draw the citric acid cycle from isocitrate to fumarate only,showing and naming each intermediate.Show where high-energy phosphate compounds or reduced electron carriers are produced or consumed,and name the enzyme that catalyzes each step.

In the citric acid cycle,a five-carbon compound is decarboxylated to yield an activated four-carbon compound.Show the substrate and product in this step,and indicate where any cofactor(s)participate(s).

Match the cofactor with its function in the citric acid cycle.A given function may be used more than once or not at all. -

In which reaction of the citric acid cycle does substrate-level phosphorylation occur?

At what point in the citric acid cycle do the methyl carbon from acetyl-CoA and the carbonyl carbon from oxaloacetate become chemically equivalent?

Show the steps of the citric acid cycle from succinyl-CoA to oxaloacetate only.For each step,show structures of substrate and product,name the enzyme responsible,and show where cofactors participate.

Germinating plant seeds can convert stored fatty acids into oxaloacetate and a variety of carbohydrates.Animals cannot synthesize significant quantities of oxaloacetate or glucose from fatty acids.What accounts for this difference?

Explain in quantitative terms the circumstances under which the following reaction can proceed. L-Malate + NAD⁺ $\rightarrow$ oxaloacetate + NADH + H⁺ $\Delta$ G'° = +29.7 kJ/mol

Show the three reactions in the citric acid cycle in which NADH is produced,including the structures.None of these reactions involves molecular oxygen (O₂),but all three reactions are strongly inhibited by anaerobic conditions;explain why.

Show the reactions by which $\alpha$ -ketoglutarate is converted to malate in the citric acid cycle.