Deck 9: Aerobic Metabolism I: The Citric Acid Cycle

Question 1

Place the following reaction intermediates of the citric acid cycle in chronological order: i. malate, ii. fumarate, iii. succinyl-CoA, iv. citrate, v.-ketoglutarate.

A) , i, ii, iv, v, iii
B) iv, v, iii, i, ii
C) iv, i, v, iii, ii
D) v, iii, i, ii, iv
E) iv, v, iii, ii, i

Answer 1

E

Question 2

Oxalosuccinate is a transient intermediate formed during which of the following reactions?

A) Citrate  Isocitrate
B) Isocitrate  -ketoglutarate
C) Pyruvate  Acetyl-CoA
D) Malate  Oxaloacetate
E) Succinyl CoA Succinate

Answer 2

B

Question 3

FADH₂ is a product of which of the following reactions?

A) Pyruvate  Acetyl CoA
B) Malate  Oxaloacetate
C) Succinyl-CoA  Succinate
D) Succinate  Fumarate
E) Succinate  Malate

Answer 3

D

Question 4

NADH is produced in which of the following reactions?

A) Malate  Fumarate
B) Succinate  Fumarate
C) -Ketoglutarate  Succinyl-CoA
D) Succinyl-CoA  Fumarate
E) Oxaloacetate  Citrate

Question 5

In the glyoxylate cycle two-carbon molecules are converted to precursors of which of the following?

A) Acetyl-CoA
B) Glucose
C) Pyruvate
D) Succinate
E) Carbon dioxide

Question 6

Which of the following enzymes is unique to the glyoxylate cycle __________?

A) Aconitase
B) Malate dehydrogenase
C) Fumarase
D) Succinate dehydrogenase
E) Isocitrate lyase

Question 7

The regulated enzymes of the citric acid cycle include _________.

A) Malate dehydrogenase
B) Fumarase
C) Citrate lyase
D) -Ketoglutarate dehydrogenase
E) Succinate thiokinase

Question 8

The enzymes involved in citrate metabolism include all of the following except _______.

A) Citrate synthase
B) Citrate lyase
C) Pyruvate carboxylase
D) Malate synthase
E) Malic enzyme

Question 9

Redox potential is best defined as

A) The tendency of one species to gain electrons
B) The tendency of one species to lose electrons
C) The tendency of a species to gain or lose electrons
D) The entropy of a reaction expressed as a voltage difference
E) None of the above is correct

Question 10

In order to determine the standard voltage of a reaction

A) The individual reaction reduction potentials must be added
B) The standard cells must be written as they occur in the reaction and the voltages are added.
C) All the reactions must be written as oxidations and the voltages are added.
D) The voltages of the individual reactions at pH = 7 must be calculated and the resultant voltages are added.
E) A standard voltage for a reaction must be determined experimentally.

Question 11

Which of the following reactions is an oxidation reaction?

A) NaOH +HCl  NaCl + H₂O
B) CH₃COOH  CH₃COO^- +H⁺
C) CH₃CHO  CH₃CH₂OH
D) CH₃CH₂OH  CH₃CHO +H₂O
E) CH₂=CH₂ + H₂O  CH₃CH₂OH

Question 12

Which of the following reactions has an oxidized product?

A) Carboxylic acid  aldehyde
B) R-SH + RSH  R-S-S-R
C) Alcohol  Ketone
D) Glutamate  -Ketoglutarate
E) None of the above are correct

Question 13

In any redox reaction, an electron donor is

A) The reducing agent
B) The oxidizing agent
C) Reduced as it accepts electrons
D) All of the above are correct
E) None of the above are correct

Question 14

In a redox reaction, an electron acceptor is

A) Oxidized as it accepts one or more electrons
B) The reducing agent
C) Converted to an electron donor with the gain of one or more electrons
D) All of the above are correct
E) None of the above are correct

Question 15

Acetyl-CoA that is consumed by the citric acid cycle is produced from which of the following biochemical pathways?

A) Glycolysis
B) Fatty acid oxidation
C) Purine catabolism
D) Urea cycle
E) Both A and B are correct

Question 16

Which of the following is the strongest reducing agent? (The standard reduction potential of each species is provided in parentheses.)

A) FADH₂ (+0.22V)
B) H₂ (+0.424V)
C) Cytochrome a-Fe⁺² (-0.29V)
D) Lactate ( + 0.19 V)
E) H₂O (+0.82V)

Question 17

Which of the following reacts with Acetyl-CoA to form citrate?

A) Succinate
B) Oxaloacetate
C) -Ketoglutarate
D) Fumarate
E) Malate

Question 18

The redox reaction in which succinate is converted to fumarate uses FAD rather than NAD⁺ because

A) FAD is a stronger oxidizing agent than NAD⁺
B) NAD⁺ is a stronger oxidizing agent than FAD
C) FAD is required for the oxidation of carboxylic acids
D) Only FAD can penetrate into mitochondria
E) NAD is not found in the cytoplasm.

Question 19

Most of the energy released during the electron transport system is used to drive
______ synthesis.

A) ATP
B) ADP
C) NADH
D) NADPH
E) Fatty acids

Question 20

Which of the following reactions requires GDP

A) Fumarate  Malate
B) Succinyl-CoA  Succinate
C) Malate  Oxaloacetate
D) Citrate  Isocitrate
E) -Ketoglutarate  Succinyl-CoA

Question 21

How many oxidations steps are there in the citric acid cycle?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 22

The product of the first reaction of the citric acid cycle is ________.

A) Acetyl-CoA
B) Oxaloacetate
C) Pyruvate
D) Lactate
E) Citrate

Question 23

Which of the following reactions involves a substrate level phosphorylation?

A) Pyruvate  Acetyl-CoA
B) Succinyl-CoA  Succinate
C) Citrate  Isocitrate
D) Fumarate  Malate
E) Malate  Oxaloacetate

Question 24

The carbon skeletons of which of the following are direct precursors of amino acids?

A) Malate
B) Succinate
C) -Ketoglutarate
D) Oxaloacetate
E) Both C and D are correct

Question 25

Which of the following is not directly required for the activity of pyruvate dehydrogenase?

A) CoASH
B) Lipoic acid
C) NAD⁺
D) ATP
E) None of the above is correct

Question 26

Which of the following is a positive effector of isocitrate dehydrogenase?

A) ADP
B) FAD
C) NADH
D) Succinyl-CoA
E) Both A and C are correct

Question 27

Consider the following reaction:
Pyruvate + NADH + H⁺ -- Lactate + NAD⁺
The half cell reaction (with their standard reduction potentials) are
Pyruvate + 2H⁺ + 2e^-  Lactate (-0.19V)
NAD⁺ + H⁺ + 2e^-  NADH (-0.32V)
What is the reduction potential for the overall reaction?

A) + 0.00V
B) + 0.03 V
C) + 0.13 V
D) +0.22 V
E) +0.15 V

Question 28

The overall reaction catalyzed by pyruvate dehydrogenase is which of the following?

A) CH₃COCHO + NAD⁺ + CoASH  CH₃CHOSCoA + NADH
B) CH₃COCOO^- + FAD +CoASH  CH₃CHSCoA + NADH
C) CH₃COCOO^- + NAD⁺ + CoASH  CH₃COSCoA + NADH
D) CH₃CH(OH)COO^- + NADH + CoASH  CH₃CH(OH)COSCoA + NAD⁺
E) None of the above is correct

Question 29

The citric acid cycle is a component of aerobic respiration. Molecular oxygen

A) Is directly involved in the reactions of the cycle
B) Is only indirectly involved in the reactions of the cycle
C) Is an important substrate for the cycle
D) Both A and C are true
E) None of the above are true.

Question 30

The main toxic effect of oxygen is due to which of the following?

A) Sulfate formation
B) ROS
C) Heat production during oxidation
D) Protons
E) Hydroxide ion

Question 31

The primordial reductive branch of the citric acid cycle was a means of producing which of the following?

A) ATP
B) NADP⁺
C) NADPH
D) NADH
E) None of the above is correct

Question 32

The primordial oxidation branch of the citric acid cycle used which of the following as the ultimate electron acceptor?

A) Pyruvate
B) Carbon dioxide
C) Oxygen
D) Sulfur
E) NAD⁺

Question 33

The enzyme, which links the two branches of the citric acid cycle, is which of the following

A) -Ketoglutarate dehydrogenase
B) Lactate dehydrogenase
C) Malate dehydrogenase
D) Fumatate reductase
E) Fumarase

Question 34

The glyoxylate cycle is a mechanism whereby plants manufacture carbohydrate from ___________.

A) Other carbohydrates
B) Amino acids
C) Fatty acids
D) Carbon dioxide
E) Phospholipids

Question 35

In biological systems most energy generating redox reactions involve hydride ion transfer or hydrogen atom transfer using which of the following?

A) NADH
B) FADH₂
C) Pyruvate
D) NADPH
E) Both A and B are correct

Question 36

Which of the following coenzymes function as an acetyl group carrier?

A) Thiamine pyrophosphate
B) Lipoic Acid
C) NADH
D) FADH₂
E) Coenzyme A

Question 37

The first of two molecules of carbon dioxide is released from which of the following compounds in the citric acid cycle?

A) Isocitrate
B) Citrate
C) -Ketoglutarate
D) Succinate
E) Fumarate

Question 38

The high-energy molecule produced in the conversion of succinyl-CoA to succinate is which of the following?

A) ATP
B) GTP
C) AMP
D) NADH
E) Both A and B are correct

Question 39

Which of the following conversions is an anaplerotic reaction of the citric acid cycle?

A) Pyruvate to oxaloacetate
B) Certain amino acids to succinyl CoA
C) Glutamate to -ketoglutarate
D) Aspartate to oxaloacetate
E) All of the above are correct

Question 40

Oxygen is useful for energy generation because

A) It is soluble in the cell membrane
B) It is abundant
C) It is a powerful reducing agent
D) It is a powerful oxidizing agent
E) A, B and D

Question 41

The most pivotal event in the history of life on earth was:

A) The development of DNA
B) The development of RNA
C) Emergence of the water splitting complex in Photosystem II
D) Development of photosynthesis
E) Adaptation to life on land

Question 42

After the evolution of oxygenic photosynthesis the release of oxygen was not immediately followed by the accumulation of oxygen in the atmosphere. This was true because

A) It was incorporated into organic molecules
B) It remained dissolved in water
C) It was consumed by oxidizable materials such as iron and ammonia
D) A and C
E) A, B and C

Question 43

Obligate anaerobes are:

A) Organisms that possess antioxidant molecules that detoxify ROS
B) Grow only in the absence of oxygen
C) Can use oxygen when it is available
D) Require oxygen to grow
E) Release oxygen

Question 44

Facultative anaerobes:

A) Organisms that possess antioxidant molecules that detoxify ROS
B) Grow only in the absence of oxygen
C) Can use oxygen when it is available
D) Require oxygen to grow
E) Release oxygen

Question 45

In eukaryotes citrate synthetase rate is controlled primarily by:

A) Availability of oxaloacetate
B) Allosteric regulators
C) Concentration of malate
D) The NADH/NAD⁺ ratio
E) Succinyl-CoA availability

Question 46

What is the difference between aerotolerant anaerobes and obligate anaerobes?

Question 47

Describe two important roles of the citric acid cycle.

Question 48

Acetyl-CoA is manufactured in the mitochondria and used in the cytoplasm to synthesize fatty acids. However acetyl-CoA cannot penetrate the mitochondrial membrane. How is this problem solved?

Question 49

How does the glyoxylate cycle differ from the citric acid cycle?

Question 50

What are the two stages of the citric acid cycle? List the products of each stage.

Question 51

Lactic acidosis occurs as a result of shock. Explain why low oxygen levels promote lactate production.

Question 52

Describe in detail the structure of the pyruvate dehydrogenase complex.

Question 53

What is an amphibolic pathway? Provide an example.

Question 54

Outline the steps of the glyoxylate cycle.

Question 55

List the biochemical processes involved in aerobic metabolism.

Question 56

What is meant by the term reduction potential?

Question 57

What is an anaplerotic reaction? Give an example.

Question 58

What is a glyoxosome? What is its function?

Question 59

Define the term reactive oxygen species. Provide examples.

Question 60

What is the function of nucleoside diphosphate kinase?

Question 61

Explain why animals cannot produce glucose from two-carbon molecules such as acetate or ethanol.

Question 62

Dichloroacetate inhibits the enzyme pyruvate dehydrogenase kinase. As a result, this compound has been used with limited success to treat lactic acidosis. Phosphorylation of the -subunit of the pyruvate dehydrogenase component of pyruvate dehydrogenase complex by pyruvate dehydrogenase kinase causes complete loss of enzymatic activity. Describe the theory behind the clinical use of dichloroacetate.

Question 63

A runner needs a tremendous amount of energy during a race. Explain how the use of ATP by contracting muscle affects the citric acid cycle.

Question 64

The citric acid cycle operates only when oxygen is present, yet oxygen is not a substrate for the cycle. Explain.

Question 65

Discuss the mechanism of control of the irreversible steps in the citric acid cycle.

Question 66

If a small amount of [1-¹⁴C] glucose is added to an aerobic yeast culture, where will the ¹⁴C initially appear in the citrate molecules?

Question 67

You have just consumed a piece of fruit. Trace the carbon atoms in the glucose in the fruit through the biochemical pathways between their uptake into liver cells and their conversion to carbon dioxide.

Question 68

What is the significance of substrate-level phosphorylation reactions? Which of the reactions of the citric acid cycle involve substrate-level phosphorylations?

Question 69

One of the many effects of chronic alcohol abuse is thiamine deficiency, caused by impaired absorption of the vitamin through the intestinal wall and diminished storage in a damaged liver. When thiamine levels are inadequate, cellular energy generation is diminished. List three enzymes involved in cellular metabolism that require thiamine. Describe the metabolic consequences of inadequate thiamine levels.

Question 70

Malonate poisons the citric acid cycle because it inhibits succinate dehydrogenase. After reviewing its structure describe how the inhibitory effect of malonate can be overcome.
Malonic Acid

Question 71

Fatty acid degradation stimulates the citric acid cycle through the activation of pyruvate carboxylase by acetyl-CoA. Why would the activation of pyruvate carboxylase increase energy generation from fatty acids?

Question 72

Describe in general terms how the appearance of molecular oxygen in Earth's atmosphere about 3 billion years ago affected the history of living organisms.

Question 73

Which steps in the citric acid cycle are regulated? Why are they regulated?

Question 74

Calculate the free energy change that occurs in the following reaction
1/2O₂ + NADH + H⁺ H₂0 + NAD⁺

Question 75

Determine the standard free energy for the following reaction
Cytochrome c (Fe⁺²) + 1/2O₂  cytochrome c (Fe⁺³) + H₂O