Question 1

Which compound is NOT required for the oxidative decarboxylation of pyruvate to form acetyl-CoA?

Accepted Answer

A)  ATP 
B)  CoA-SH 
C)  FAD 
D)  lipoic acid 
E)  NAD+ 
A)  ATP 
B)  CoA-SH 
C)  FAD 
D)  lipoic acid 
E)  NAD+

Question 2

Which cofactor is required for the conversion of succinate to fumarate in the citric acid cycle?

Accepted Answer

A)  ATP 
B)  biotin 
C)  FAD 
D)  NAD+ 
E)  NADP+ 
A)  ATP 
B)  biotin 
C)  FAD 
D)  NAD+ 
E)  NADP+

Question 3

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

Accepted Answer

The given reaction is the conversion of

Question 4

During the reaction of pyruvate carboxylase, CO2 is NOT covalently attached to:

Accepted Answer

A)  phosphate. 
B)  biotin. 
C)  pyruvate. 
D)  lysine. 
E)  All of the answers are correct. 
A)  phosphate. 
B)  biotin. 
C)  pyruvate. 
D)  lysine. 
E)  All of the answers are correct.

Question 5

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.

Accepted Answer

Sure, here are the structures of the rea

Question 6

Match the cofactors below with their roles in the pyruvate dehydrogenase complex reaction.
Cofactors:
A. Coenzyme A (CoA-SH)
B. NAD+
C. Thiamine pyrophosphate (TPP)
D. FAD
E. Lipoic acid in oxidized form
Roles:
_______ Attacks and attaches to the central carbon in pyruvate
_______ Oxidizes FADH2
_______ Accepts the acetyl group from reduced lipoic acid
_______ Oxidizes the reduced form of lipoic acid
_______ Initial electron acceptor in oxidation of pyruvate.

Accepted Answer

The pyruvate dehydrogenase complex (PDC)

Question 7

Anaplerotic reactions:

Accepted Answer

A)  produce oxaloacetate and malate to maintain constant levels of citric acid cycle intermediates. 
B)  produce biotin needed by pyruvate carboxylase. 
C)  recycle pantothenate used to make CoA. 
D)  produce pyruvate and citrate to maintain constant levels of citric acid cycle intermediates. 
E)  All of the answers are correct. 
A)  produce oxaloacetate and malate to maintain constant levels of citric acid cycle intermediates. 
B)  produce biotin needed by pyruvate carboxylase. 
C)  recycle pantothenate used to make CoA. 
D)  produce pyruvate and citrate to maintain constant levels of citric acid cycle intermediates. 
E)  All of the answers are correct.

Question 8

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

Accepted Answer

Fluorocitrate is a deadly poison because

Question 9

Which statement about the oxidative decarboxylation of pyruvate in animal cells is CORRECT?

Accepted Answer

A)  One of the products of this reaction is a molecule containing a thioether bond. 
B)  It only occurs under aerobic conditions. 
C)  The process occurs in the glyoxysome compartment of the cell. 
D)  It is often considered the first step in the glyoxylate cycle, as it generates acetyl-CoA, which is required by this pathway. 
E)  It is the most important anaplerotic reaction in hepatocytes. 
A)  One of the products of this reaction is a molecule containing a thioether bond. 
B)  It only occurs under aerobic conditions. 
C)  The process occurs in the glyoxysome compartment of the cell. 
D)  It is often considered the first step in the glyoxylate cycle, as it generates acetyl-CoA, which is required by this pathway. 
E)  It is the most important anaplerotic reaction in hepatocytes.

Question 10

Which molecule is an $\alpha$-keto acid?

Accepted Answer

A)  oxaloacetate 
B)  citrate 
C)  $\alpha$-ketoglutarate 
D)  oxaloacetate and $\alpha$-ketoglutarate 
E)  citrate and $\alpha$-ketoglutarate 
A)  oxaloacetate 
B)  citrate 
C)  $\alpha$-ketoglutarate 
D)  oxaloacetate and $\alpha$-ketoglutarate 
E)  citrate and $\alpha$-ketoglutarate

Question 11

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

Accepted Answer

In the citric acid cycle (also known as

Question 12

Shown below is a list of pairs of compounds. In which pair is the second compound produced by a reduction of the first compound?

Accepted Answer

A)  fumarate and succinate 
B)  oxaloacetate and citrate 
C)  fumarate and malate 
D)  malate and oxaloacetate 
E)  isocitrate and $\alpha$-ketoglutarate 
A)  fumarate and succinate 
B)  oxaloacetate and citrate 
C)  fumarate and malate 
D)  malate and oxaloacetate 
E)  isocitrate and $\alpha$-ketoglutarate

Question 13

The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP) by substrate level phosphorylation is the conversion of:

Accepted Answer

A)  citrate to isocitrate. 
B)  fumarate to malate. 
C)  malate to oxaloacetate. 
D)  succinate to fumarate. 
E)  succinyl-CoA to succinate. 
A)  citrate to isocitrate. 
B)  fumarate to malate. 
C)  malate to oxaloacetate. 
D)  succinate to fumarate. 
E)  succinyl-CoA to succinate.

Question 14

Name a metabolite that is required for pyruvate carboxylase activity (NOT part of the reaction), and explain why this makes metabolic sense.

Accepted Answer

A metabolite that is required for pyruva

Question 15

The standard reduction potentials (E'°) for the following half reactions are given. Fumarate + 2H+ + 2e- $\rightarrow$ succinate
E'° = +0.031 V
FAD + 2H+ + 2e- $\rightarrow$FADH2
E'° = -0.219 V
If succinate, fumarate, FAD, and FADH2, all at l M concentrations, were mixed together in the presence of succinate dehydrogenase, which of the following would happen initially?

Accepted Answer

A)  Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced. 
B)  Fumarate would become reduced; FADH2 would become oxidized. 
C)  No reaction would occur because all reactants and products are already at their standard concentrations. 
D)  Succinate would become oxidized; FAD would become reduced. 
E)  Succinate would become oxidized; FADH2 would be unchanged because it is a cofactor, not a substrate. 
A)  Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced. 
B)  Fumarate would become reduced; FADH2 would become oxidized. 
C)  No reaction would occur because all reactants and products are already at their standard concentrations. 
D)  Succinate would become oxidized; FAD would become reduced. 
E)  Succinate would become oxidized; FADH2 would be unchanged because it is a cofactor, not a substrate.

Question 16

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).

Accepted Answer

Beriberi is caused by a deficiency of th

Question 17

What process occurs in the citric acid cycle?

Accepted Answer

A)  formation of a mixed anhydride (acyl phosphate) 
B)  net synthesis of oxaloacetate from two acetyl-CoA molecules 
C)  hydrolysis of two thioester bonds 
D)  All of the answers are correct. 
E)  None of the answers is correct. 
A)  formation of a mixed anhydride (acyl phosphate) 
B)  net synthesis of oxaloacetate from two acetyl-CoA molecules 
C)  hydrolysis of two thioester bonds 
D)  All of the answers are correct. 
E)  None of the answers is correct.

Question 18

Which statement about NAD+ and NADH is TRUE?

Accepted Answer

A)  NADH inhibits the pyruvate dehydrogenase complex. 
B)  NAD+ is oxidized to NADH by the $\alpha$-ketoglutarate dehydrogenase complex. 
C)  NAD+ is a coenzyme for two of the enzymes in the pyruvate dehydrogenase complex. 
D)  NAD+ is oxidized to NADH by isocitrate dehydrogenase. 
E)  NAD+ is oxidized to NADH by both isocitrate dehydrogenase and the$\alpha$-ketoglutarate dehydrogenase complex. 
A)  NADH inhibits the pyruvate dehydrogenase complex. 
B)  NAD+ is oxidized to NADH by the $\alpha$-ketoglutarate dehydrogenase complex. 
C)  NAD+ is a coenzyme for two of the enzymes in the pyruvate dehydrogenase complex. 
D)  NAD+ is oxidized to NADH by isocitrate dehydrogenase. 
E)  NAD+ is oxidized to NADH by both isocitrate dehydrogenase and the$\alpha$-ketoglutarate dehydrogenase complex.

Question 19

Covalent modification is one way the activity of specific enzymes can be regulated. Which enzyme is NOT regulated in this way?

Accepted Answer

A)  phosphofructokinase-2 
B)  $\alpha$-ketoglutarate dehydrogenase 
C)  pyruvate dehydrogenase 
D)  phosphorylase kinase 
E)  All of these enzymes are regulated by covalent modification. 
A)  phosphofructokinase-2 
B)  $\alpha$-ketoglutarate dehydrogenase 
C)  pyruvate dehydrogenase 
D)  phosphorylase kinase 
E)  All of these enzymes are regulated by covalent modification.

Question 20

The disease beriberi is caused by a deficiency of thiamine in the diet. Why is this disease often associated with metabolic acidosis and neurological disorders?

Accepted Answer

Beriberi is a disease caused by a defici

Exam 16: The Citric Acid Cycle

Which compound is NOT required for the oxidative decarboxylation of pyruvate to form acetyl-CoA?

Which cofactor is required for the conversion of succinate to fumarate in the citric acid cycle?

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

During the reaction of pyruvate carboxylase, CO2 is NOT covalently attached to:

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.

Anaplerotic reactions:

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

Which statement about the oxidative decarboxylation of pyruvate in animal cells is CORRECT?

Which molecule is an α\alphaα -keto acid?

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

Shown below is a list of pairs of compounds. In which pair is the second compound produced by a reduction of the first compound?

The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP) by substrate level phosphorylation is the conversion of:

Name a metabolite that is required for pyruvate carboxylase activity (NOT part of the reaction), and explain why this makes metabolic sense.

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).

What process occurs in the citric acid cycle?

Which statement about NAD+ and NADH is TRUE?

Covalent modification is one way the activity of specific enzymes can be regulated. Which enzyme is NOT regulated in this way?

The disease beriberi is caused by a deficiency of thiamine in the diet. Why is this disease often associated with metabolic acidosis and neurological disorders?

The Foundations of Biochemistry

Water

Amino Acids, Peptides, and Proteins

The Three-Dimensional Structure of Proteins

Protein Function

Enzymes

Carbohydrates and Glycobiology

Nucleotides and Nucleic Acids

DNA-Based Information Technologies

Lipids

Biological Membranes and Transport

Biosignaling

Bioenergetics and Biochemical Reaction Types

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway

Principles of Metabolic Regulation

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

Oxidative Phosphorylation and Photophosphorylation

Carbohydrate Biosynthesis in Plants and Bacteria

Lipid Biosynthesis

Biosynthesis of Amino Acids, Nucleotides, and Related Molecules

Hormonal Regulation and Integration of Mammalian Metabolism

Genes and Chromosomes

DNA Metabolism

RNA Metabolism

Protein Metabolism

Regulation of Gene Expression

Filters

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

During the reaction of pyruvate carboxylase, CO₂ is NOT covalently attached to:

Which molecule is an $\alpha$ -keto acid?

Which statement about NAD⁺ and NADH is TRUE?