Question 1

Which statement is NOT true of electron transport?

Accepted Answer

A)  The mobile electron carrier coenzyme A is located in the inner mitochondrial membrane. 
B)  Electrons flow from redox centers with a lower reduction potential to redox centers with a higher reduction potential. 
C)  The electron transport chain oxidizes reduced cofactors. 
D)  Cytochrome C has a higher reduction potential than FADH2. 
E)  None of the statements is true. 
A)  The mobile electron carrier coenzyme A is located in the inner mitochondrial membrane. 
B)  Electrons flow from redox centers with a lower reduction potential to redox centers with a higher reduction potential. 
C)  The electron transport chain oxidizes reduced cofactors. 
D)  Cytochrome C has a higher reduction potential than FADH2. 
E)  None of the statements is true.

Question 2

Antimycin A blocks electron transfer between cytochromes b and c1. If intact mitochondria were incubated with antimycin A, excess NADH, and an adequate supply of O2, which compound would be found in the oxidized state?

Accepted Answer

A)  coenzyme Q 
B)  cytochrome a3 
C)  cytochrome b 
D)  cytochrome e 
E)  cytochrome f 
A)  coenzyme Q 
B)  cytochrome a3 
C)  cytochrome b 
D)  cytochrome e 
E)  cytochrome f

Question 3

What effect will increasing the number of c subunits in ATP synthase have on the P:O ratio?

Accepted Answer

A)  It will increase for both NADH and FADH2. 
B)  It will increase for NADH and decrease for FADH2. 
C)  It will decrease for NADH and increase for FADH2. 
D)  It will decrease for both NADH and FADH2. 
E)  It will remain unchanged for both NADH and FADH2. 
A)  It will increase for both NADH and FADH2. 
B)  It will increase for NADH and decrease for FADH2. 
C)  It will decrease for NADH and increase for FADH2. 
D)  It will decrease for both NADH and FADH2. 
E)  It will remain unchanged for both NADH and FADH2.

Question 4

What factor makes the outer mitochondrial membrane permeable to protons?

Accepted Answer

A)  proton symports 
B)  proton antiports 
C)  porins 
D)  the presence of proton ionophores 
E)  the presence of negatively charged lipids 
A)  proton symports 
B)  proton antiports 
C)  porins 
D)  the presence of proton ionophores 
E)  the presence of negatively charged lipids

Question 5

How many of cytochrome c need to be reoxidized for every oxygen molecule (O2) converted to water?

Accepted Answer

A)  one 
B)  two 
C)  three 
D)  four 
E)  eight 
A)  one 
B)  two 
C)  three 
D)  four 
E)  eight

Question 6

Show the path of electrons from ubiquinone (Q or coenzyme Q) to oxygen in the mitochondrial respiratory chain. One of the two compounds (Q and O2) has a standard reduction potential (E'°) of 0.82 V, and the other, 0.045 V. Which value belongs to each compound? How did you deduce this?

Accepted Answer

The compound with a standard reduction p

Question 7

Which component of the electron-transport chain is NOT an integral membrane protein?

Accepted Answer

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

Question 8

When the $\Delta$G'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme, it is found to be close to zero. This is thought to be due to:

Accepted Answer

A)  a very low energy of activation. 
B)  enzyme-induced oxygen exchange. 
C)  stabilization of ADP relative to ATP by enzyme binding. 
D)  stabilization of ATP relative to ADP by enzyme binding. 
E)  None of the answers is correct. 
A)  a very low energy of activation. 
B)  enzyme-induced oxygen exchange. 
C)  stabilization of ADP relative to ATP by enzyme binding. 
D)  stabilization of ATP relative to ADP by enzyme binding. 
E)  None of the answers is correct.

Question 9

The electron-transport chain and ATP synthase are effectively coupled. Which statement BEST describes how this occurs?

Accepted Answer

A)  The electron-transport chain reoxidizes reduced cofactors. 
B)  The electron-transport chain generates an electrochemical gradient that provides energy for the production of ATP. 
C)  ATP synthase utilizes oxidized cofactors. 
D)  Through a series of conformational changes, ATP synthase generates ATP. 
A)  The electron-transport chain reoxidizes reduced cofactors. 
B)  The electron-transport chain generates an electrochemical gradient that provides energy for the production of ATP. 
C)  ATP synthase utilizes oxidized cofactors. 
D)  Through a series of conformational changes, ATP synthase generates ATP.

Question 10

What is the P:O ratio for electrons entering the electron-transport chain that originate from reoxidation of acyl-CoA dehydrogenase?

Accepted Answer

A)  greater than the P:O ratio for NADH reoxidation 
B)  approximately the same as the P:O ratio for NADH reoxidation 
C)  less than the P:O ratio for NADH reoxidation but more than the P:O ratio for Complex II reoxidation 
D)  approximately the same as the P:O ratio for Complex II reoxidation 
E)  less than the P:O ratio for Complex II reoxidation 
A)  greater than the P:O ratio for NADH reoxidation 
B)  approximately the same as the P:O ratio for NADH reoxidation 
C)  less than the P:O ratio for NADH reoxidation but more than the P:O ratio for Complex II reoxidation 
D)  approximately the same as the P:O ratio for Complex II reoxidation 
E)  less than the P:O ratio for Complex II reoxidation

Question 11

Cytochrome c can be reduced directly by small molecules such as ascorbate (vitamin C). If ascorbate is added to the following preparations of mitochondria (which include succinate and oxygen), what would you predict would be the effect on oxygen consumption in each case, and why?
a.     mitochondria that have been treated with oligomycin
b.     mitochondria that have been treated with cyanide
c.     mitochondria that have been treated with rotenone
d.     mitochondria that have been treated with antimycin A

Accepted Answer

a. If ascorbate is added to mitochondria

Question 12

Reduced QH2 is NOT formed by which of the following?

Accepted Answer

A)  Complex I and NADH 
B)  Complex II and succinate 
C)  Complex III and cytochrome c 
D)  fatty acid oxidation 
E)  oxidation of glycerol-3-phosphate 
A)  Complex I and NADH 
B)  Complex II and succinate 
C)  Complex III and cytochrome c 
D)  fatty acid oxidation 
E)  oxidation of glycerol-3-phosphate

Question 13

Which characteristic describes heme a but not heme c?

Accepted Answer

A)  noncovalently associated prosthetic group 
B)  contains an isoprenoid structure 
C)  contains an aldehyde substituent on the porphyrin ring 
D)  contains two propionate substituents on the porphyrin ring 
E)  contains a vinyl substituent on the porphyrin ring 
A)  noncovalently associated prosthetic group 
B)  contains an isoprenoid structure 
C)  contains an aldehyde substituent on the porphyrin ring 
D)  contains two propionate substituents on the porphyrin ring 
E)  contains a vinyl substituent on the porphyrin ring

Question 14

As you read and answer this question, you are (presumably) consuming oxygen. What single reaction accounts for most of your oxygen consumption?

Accepted Answer

The single reaction that accounts for mo

Question 15

The standard reduction potential for ubiquinone (Q or coenzyme Q) is 0.045 V, and the standard reduction potential (E'°) for FAD is -0.219 V. Using these values, show that the oxidation of FADH2 by ubiquinone theoretically liberates enough energy to drive the synthesis of ATP. The Faraday constant,  , is 96.48 kJ/V · mol. $\Delta$G'° for ATP synthesis is +30.5 kJ/mol.

Accepted Answer

To determine if the oxidation of FADH2 b

Question 16

In some organisms, an alternative oxidase will accept electrons from ubiquinol and reduce oxygen to water with no associated proton translocation. What would be a consequence of having this oxidase active?

Accepted Answer

A)  decreased rate of NADH reoxidation 
B)  decreased P:O ratio 
C)  decreased rate of oxygen consumption 
D)  inhibition of oxidative pathways like the citric acid cycle 
E)  increased sensitivity to cyanide poisoning 
A)  decreased rate of NADH reoxidation 
B)  decreased P:O ratio 
C)  decreased rate of oxygen consumption 
D)  inhibition of oxidative pathways like the citric acid cycle 
E)  increased sensitivity to cyanide poisoning

Question 17

During electron transfer through the mitochondrial respiratory chain, the overall reaction is NADH + 1/2 O2 + H+$\rightarrow$NAD+ + H2O. The difference in reduction potentials for the two half-reactions ($\Delta$E'°) is +1.14 V. Show how you would calculate the standard free-energy change, $\Delta$G'°, for the reaction as written above. (The Faraday constant,  , is 96.48 kJ/V · mol.)

Accepted Answer

To calculate the standard free-energy ch

Question 18

Compound X is an inhibitor of mitochondrial ATP synthesis. It was observed that when compound X was added to cells, the NAD+/NADH ratio decreased. Would you expect X to be an uncoupling agent or an inhibitor of respiratory electron transfer? Explain.

Accepted Answer

Based on the observation that the NADH/N

Question 19

In normal mitochondria, the rate of NADH consumption (oxidation) will:

Accepted Answer

A)  be increased in active muscle, decreased in inactive muscle. 
B)  be very low if the ATP synthase is inhibited, but increase when an uncoupler is added. 
C)  decrease if mitochondrial ADP is depleted. 
D)  decrease when cyanide is used to prevent electron transfer through the cytochrome a + a3 complex. 
E)  All of the answers are correct. 
A)  be increased in active muscle, decreased in inactive muscle. 
B)  be very low if the ATP synthase is inhibited, but increase when an uncoupler is added. 
C)  decrease if mitochondrial ADP is depleted. 
D)  decrease when cyanide is used to prevent electron transfer through the cytochrome a + a3 complex. 
E)  All of the answers are correct.

Question 20

A new compound isolated from mitochondria is claimed to represent a previously unrecognized carrier in the electron transfer chain. It is given the name coenzyme Z. Which line of evidence do you feel is the LEAST conclusive in assigning this compound a position in the electron transfer chain?

Accepted Answer

A)  Alternate oxidation and reduction of the mitochondrion-bound coenzyme Z can be readily demonstrated. 
B)  Removal of coenzyme Z from the mitochondria results in a decreased rate of oxygen consumption. 
C)  The rate of oxidation and reduction of mitochondrion-bound coenzyme is of the same order of magnitude as the overall rate of electron transfer in mitochondria as measured by oxygen consumption. 
D)  The reduction potential of Z is between that of two compounds known to participate in the electron transport chain 
E)  When added to a mitochondrial suspension, coenzyme Z is taken up very rapidly and specifically by the mitochondria. 
A)  Alternate oxidation and reduction of the mitochondrion-bound coenzyme Z can be readily demonstrated. 
B)  Removal of coenzyme Z from the mitochondria results in a decreased rate of oxygen consumption. 
C)  The rate of oxidation and reduction of mitochondrion-bound coenzyme is of the same order of magnitude as the overall rate of electron transfer in mitochondria as measured by oxygen consumption. 
D)  The reduction potential of Z is between that of two compounds known to participate in the electron transport chain 
E)  When added to a mitochondrial suspension, coenzyme Z is taken up very rapidly and specifically by the mitochondria.

Exam 19: Oxidative Phosphorylation and Photophosphorylation

Which statement is NOT true of electron transport?

Antimycin A blocks electron transfer between cytochromes b and c1. If intact mitochondria were incubated with antimycin A, excess NADH, and an adequate supply of O2, which compound would be found in the oxidized state?

What effect will increasing the number of c subunits in ATP synthase have on the P:O ratio?

What factor makes the outer mitochondrial membrane permeable to protons?

How many of cytochrome c need to be reoxidized for every oxygen molecule (O2) converted to water?

Show the path of electrons from ubiquinone (Q or coenzyme Q) to oxygen in the mitochondrial respiratory chain. One of the two compounds (Q and O2) has a standard reduction potential (E'°) of 0.82 V, and the other, 0.045 V. Which value belongs to each compound? How did you deduce this?

Which component of the electron-transport chain is NOT an integral membrane protein?

When the Δ\DeltaΔ G'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme, it is found to be close to zero. This is thought to be due to:

The electron-transport chain and ATP synthase are effectively coupled. Which statement BEST describes how this occurs?

What is the P:O ratio for electrons entering the electron-transport chain that originate from reoxidation of acyl-CoA dehydrogenase?

Reduced QH2 is NOT formed by which of the following?

Which characteristic describes heme a but not heme c?

As you read and answer this question, you are (presumably) consuming oxygen. What single reaction accounts for most of your oxygen consumption?

In some organisms, an alternative oxidase will accept electrons from ubiquinol and reduce oxygen to water with no associated proton translocation. What would be a consequence of having this oxidase active?

Compound X is an inhibitor of mitochondrial ATP synthesis. It was observed that when compound X was added to cells, the NAD+/NADH ratio decreased. Would you expect X to be an uncoupling agent or an inhibitor of respiratory electron transfer? Explain.

In normal mitochondria, the rate of NADH consumption (oxidation) will:

A new compound isolated from mitochondria is claimed to represent a previously unrecognized carrier in the electron transfer chain. It is given the name coenzyme Z. Which line of evidence do you feel is the LEAST conclusive in assigning this compound a position in the electron transfer chain?

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

The Citric Acid Cycle

Fatty Acid Catabolism

Amino Acid Oxidation and the Production of Urea

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

Antimycin A blocks electron transfer between cytochromes b and c₁. If intact mitochondria were incubated with antimycin A, excess NADH, and an adequate supply of O₂, which compound would be found in the oxidized state?

How many of cytochrome c need to be reoxidized for every oxygen molecule (O₂) converted to water?

Show the path of electrons from ubiquinone (Q or coenzyme Q) to oxygen in the mitochondrial respiratory chain. One of the two compounds (Q and O₂) has a standard reduction potential (E'°) of 0.82 V, and the other, 0.045 V. Which value belongs to each compound? How did you deduce this?

When the $\Delta$ G'° of the ATP synthesis reaction is measured on the surface of the ATP synthase enzyme, it is found to be close to zero. This is thought to be due to:

Reduced QH₂ is NOT formed by which of the following?

Compound X is an inhibitor of mitochondrial ATP synthesis. It was observed that when compound X was added to cells, the NAD⁺/NADH ratio decreased. Would you expect X to be an uncoupling agent or an inhibitor of respiratory electron transfer? Explain.