Deck 17: Mitochondrial Functions and Oxidative Phosphorylation

Question 1

You are studying the effects of a compound on the respiratory activity of isolated mitochondria. Your experiments demonstrate that oxygen consumption is normal when pyruvate and malate are used as well as when succinate is added. However, you find that the production of ATP is severely impaired with addition of the compound. These results most closely resemble the effects that would be seen by the addition of the following electron transport inhibitor to your system?

A) antimycin A
B) azide
C) dinitrophenol (DNP)
D) oligomycin
E) rotenone

Answer 1

dinitrophenol (DNP)

Question 2

A laboratory analysis of isolated mitochondria demonstrates that oxygen consumption is normal when succinate is added but extremely low when pyruvate and malate are used. The mitchondria are subsequently shown to have normal cytochromes but a reduced iron content. The reduced pyruvate/malate oxidation is due to a defect in which of the following respiratory components?

A) cytochrome c
B) cytochrome oxidase
C) NADH dehydrogenase
D) succinate dehydrogenase
E) ubiquinone

Answer 2

NADH dehydrogenase

Question 3

Which of the following statements best characterizes ATP synthase?

A) it couples ATP export from the mitochondrial matrix to ATP synthesis
B) it is soluble protein found in the mitochondrial matrix
C) its catalytic function is to synthesize ATP in a reaction driven by a chemiosmotic potential
D) oligomycin binds to ATP synthase, directly preventing ATP export
E) the low H+ ion concentration outside mitochondria establishes an electrochemical gradient that drives ATP synthesis

Answer 3

its catalytic function is to synthesize ATP in a reaction driven by a chemiosmotic potential

Question 4

Which of the following enzymes catalyzes the reaction shown?
Fe²⁺ + O₂ + 4H⁺ → 2H₂O + Fe³⁺

A) catalase
B) cytochrome c oxidase
C) cytochrome P450
D) peroxidase
E) superoxide dismutase

Question 5

You are studying the effects of a compound on the respiratory activity of isolated mitochondria. Your experiments demonstrate that oxygen consumption increases as expected when pyruvate and malate are used as well as when succinate is added. Addition of the test compound results in a significant rate of oxygen consumption. These results most closely resemble the effects that would be seen by the addition of which of the following to your system?

A) antimycin A
B) carbon monoxide
C) cyanide
D) dinitrophenol
E) rotenone

Question 6

A 9-year-old girl is brought to her physician for an assessment of potential causes for her increased vision problems. Examination demonstrates that her eye movement is impaired and she has pigmentary retinopathy. Her physician suspects the child has Kearns-Sayre syndrome which is caused by a defect in complex II of the electron transport chain. If this diagnosis is correct, oxidation of which of the following substrates would be associated with impaired electron transfer?

A) acetyl-CoA
B) α-ketoglutarate
C) malate
D) pyruvate
E) succinate

Question 7

Reduced ubiquinone, generated during the oxidation of NADH, passes its electrons to which of the following?

A) ATP synthase
B) cytochrome c oxidase (complex IV)
C) cytochrome b
D) cytochrome c
E) molecular oxygen

Question 8

In cases of acute cyanide poisoning, cyanide binds to the Fe³⁺ of a cytochrome. Which statement best describes this cytochrome?

A) binds carbon monoxide
B) directly oxidized by cytochrome c
C) directly oxidizes cytochrome b
D) found in the mitochondrial matrix
E) reduces cytochrome c

Question 9

You are the physician examining a 6-year-old boy who has been experiencing progressive muscle weakness. You perform assays on muscle biopsy tissue from this patient and find that mitochondrial oxidation of succinate is normal but that pyruvate
Oxidation is severely impaired. Mitochondrial extracts demonstrate that the activity of the pyruvate dehydrogenase complex (PDHc) is normal as is the activity of malate dehydrogenase. These results are consistent with the patient harboring a defect in which of the following mitochondrial components?

A) ATP synthase
B) complex I
C) complex II
D) complex III
E) complex IV

Question 10

You are carrying out experiments on isolated skeletal muscle mitochondria. For these experiments you are using malate as the oxidizable substrate. Following the addition of malate you add the electron transport inhibitor cyanide. You then examine the oxidation state of various components of the electron transport chain. Which of the following would be expected to be in an oxidized state following this experiment?

A) coenzyme Q
B) complex I
C) complex II
D) complex III
E) cytochrome c

Question 11

A 6-year-old boy is brought to his pediatrician because his parents are concerned about the appearance of seizures and stroke-like episodes. Upon examination the parents reveal that their son has recently begun to exhibit a progressive incoordination in his walking and also difficulty picking up his toys. The physician notes that the patient is short for his age and an eye examination reveals pigmentary retinopathy. Analysis of blood shows elevated levels of lactic acid. These signs and symptoms are most indicative of which of the following disorders?

A) erythrocyte pyruvate kinase deficiency
B) Kearns-Sayre syndrome (KSS)
C) Leigh syndrome
D) mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS)
E) Type 2 diabetes

Question 12

Which of the following components of mitochondrial electron transport can act as 1-electron or 2-electron carriers?

A) coenzyme Q and flavins
B) cytochrome c, coenzyme Q, and flavins
C) NADH, non-heme iron, cytochrome c, coenzyme Q, and flavins
D) non-heme iron, cytochrome c, coenzyme Q, and flavins

Question 13

Which of the following components of the electron transport system is inhibited by oligomycin?

A) ATP synthase
B) complex I
C) complex II
D) complex III
E) complex IV

Question 14

The standard reduction potentials (E0') for the following half reactions are given.
Fumarate + 2H⁺ + 2^e− → succinate E^0' = + 0.031 V
FAD + 2H⁺ + 2^e− → FADH₂ E^0' = −0.219 V
If you mixed succinate, fumarate, FAD, and FADH₂ together, all at 1-M concentrations and in the presence of succinate dehydrogenase, which of the following would happen initially?

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

Question 15

You are examining a 1-year-old infant who is presenting with liver failure and suffers from frequent seizures. An analysis of mitochondrial function from a skeletal muscle biopsy shows a significant respiratory deficit. A molecular analysis shows that there is a deletion of the mtDNA encompassing the gene encoding DNA polymerase g. This patient is most likely suffering from which of the following diseases?

A) Alpers disease
B) Kearns-Sayre syndrome
C) Leigh syndrome
D) MELAS
E) myoclonic epilepsy and ragged red fiber disease (MERRF)

Question 16

Obesity is associated with hyperlipidemia resulting in an increased delivery of fatty acid to most tissues including the pancreas. Excess fatty acid oxidation in β-cells of the pancreas results in increased reactive oxygen species (ROS) production. The increased ROS production ultimately contributes to β-cell apoptosis and the need for exogenous insulin in poorly controlled Type 2 diabetes. The deleterious effects of ROS within the pancreas are amplified due to limited expression of which of the following?

A) caspase 9
B) catalase
C) glutathione peroxidase
D) peroxiredoxin
E) superoxide dismutase

Question 17

Which of the following best explains how the brown adipose tissue in newborns generates large amounts of heat?

A) decreased availability of carnitine
B) increased availability of carnitine
C) increased availability of fat
D) increased formation of ATP
E) mitochondrial leak of hydrogen ions

Question 18

A 21-year-old man is brought to the ER after being found unconscious. He is gasping, and respirations are 24/min. There is evidence that he has vomited recently. Two capsules containing potassium cyanide are found in his shirt pocket. Blood lactate concentration is 3.3 mEq/L (normal = 0.8 ± 0.4 mEq/L). Which of the following processes is most likely inhibited in this patient?

A) conversion of pyruvate to alanine
B) glycolysis
C) mitochondrial electron transport
D) mobilization of fatty acids from adipose tissue
E) release of insulin from pancreas

Question 19

Addition of an uncoupling agent to respiring mitochondria carrying out oxidative phosphorylation has which of the following metabolic effects?

A) activity of the TCA cycle ceases
B) ATP formation ceases, but O₂ consumption continues
C) fatty acid oxidation ceases
D) formation of ATP continues, but O₂ consumption ceases
E) NADH oxidation ceases

Question 20

The electron transport chain of mammalian mitochondria contains 3 multienzyme protein complexes that convert the energy of oxidationreduction reactions into a form that can be used for the synthesis of ATP and for the uptake of solutes. This form of energy is most likely an example of which of the following?

A) high-energy phosphorylated ester
B) phosphocreatine
C) proton gradient only
D) sodium gradient only
E) sodium and potassium gradient

Question 21

Which of the following is the most likely mechanism of action of a pharmacological agent that prevents ATP generation in isolated mitochondria?

A) activation of cytochrome c
B) decrease of NADH generation by NADH dehydrogenase
C) disruption of pH gradient across mitochondrial membrane
D) increase of transport of pyruvate through the mitochondrial membrane
E) inhibition of glyceraldehydes-3-phosphate dehydrogenase

Question 22

According to the chemiosmotic theory of how oxidation and phosphorylation are coupled, which of the following processes produces the chemical gradient that drives the generation of ATP from ADP?

A) electron transport causes H+ to penetrate the inner mitochondrial membrane
B) electron transport ejects H+ into the intermembrane space
C) FADH2 is regenerated from FAD
D) NADH is regenerated from NAD+
E) osmotic forces cause H+ to bind with FAD in the mitochondrial matrix

Question 23

In a study of the regulation of body weight, the administration of exogenous leptin to mice is found to increase the activity of proton leak channels located in the inner membrane of mitochondria in adipose tissue cells. Which of the following is most likely to increase as a result of the increased transport of protons through these mitochondrial leak channels?

A) heat production
B) mitochondrial NADH concentrations
C) mitochondrial synthesis of ATP
D) NADH reduction from NAD₊
E) pH of the mitochondrial matrix

Question 24

In newborns, brown fat plays an important role in the generation of heat through which of the following actions?

A) blocking the action of hormone-sensitive lipase
B) increasing the rate of thyroxine synthesis
C) inducing of shivering by leptin
D) promoting proton leakage into mitochondria without ATP formation
E) uncoupling gluconeogenesis from triglyceride hydrolysis