Biochemistry : Other Electron Transport Chain Concepts

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #31 : Electron Transport And Oxidative Phosphorylation

A drug is introduced into cells that affects the mechanics of the electron transport chain. Specifically, this drug completely inhibits the flow of electrons through the electron transport chain and also completely halts the synthesis of ATP. Which of the following drugs is capable of doing this, and how is it accomplished?

Possible Answers:

Allopurinol, which acts as a suicide inhibitor of xanthine oxidase

Dinitrophenol, which acts as a proton uncoupler by shuttling protons across the inner mitochondrial membrane

Oligomycin, which inhibits ATP synthase

Methotrexate, which acts as a competitive inhibitor of dihydrofolate reductase

Cyanide, which inhibits the activity of cytochrome C oxidase

Correct answer:

Cyanide, which inhibits the activity of cytochrome C oxidase

Explanation:

The correct answer is cyanide. This compound acts to inhibit cytochrome C oxidase, otherwise known as Complex IV of the electron transport chain. By inhibiting this complex, cyanide effectively halts the flow of electrons through the chain. Consequently, protons are not able to be pumped from the matrix to the intermembrane space and thus, a proton gradient cannot be established. Without a proton gradient, protons will not flow through ATP synthase, hence no ATP will be produced.

Oligomycin, on the other hand, acts to inhibit ATP synthase, which means that ATP will not be able to be produced. However, electrons are still able to flow through the chain, which means that protons are still able to be pumped across the inner membrane.

Dinitrophenol is a relatively nonpolar compound that is able to situate itself into the inner mitochondrial membrane. In doing so, it is able to dissipate the proton gradient by allowing protons to essentially be transported from the intermembrane space to the matrix without traversing through ATP synthase. Even though protons can still flow through ATP synthase to generate ATP in this scenario, the proton gradient won't be nearly as potent because they now have an alternative route to the matrix.

Methotrexate acts to competitively inhibit the enzyme known as dihydrofolate reductase. This enzyme has nothing to do with the electron transport chain, and thus will have no effect on ATP synthesis. Commonly, this drug is used as an anti-cancer agent because its substrate, dihydrofolate, is a compound that is used in the syntheis of thymine nucleotides for DNA synthesis. Inhibiting dihydrofolate reductase effectively reduces the production of thymine, which can negatively impact DNA replication in rapidly dividing cancer cells.

Likewise, allopurinol has nothing to do with the electron transport chain. This drug acts as an inhibitor of the enzyme xanthine oxidase, which is responsible for synthesizing uric acid. High levels of uric acid can lead to the development of gout, and thus, this drug is typically used to help treat people suffering from gout.

Example Question #32 : Electron Transport And Oxidative Phosphorylation

Which of the following is an inhibitor of the inner mitochondrial proton gradient?

Possible Answers:

Oligomycin

Dinitrophenol

Fructose 2,6-biphosphate

Potassium cyanide

Rotenone

Correct answer:

Dinitrophenol

Explanation:

Potassium cyanide inhibits cellular respiration by acting on mitochondrial cytochrome c reductase (leading to hypoxia and death). Rotenone also affects oxidative phosphorylation, by inhibiting electron transfer from cytochrome 1 to ubiquinone, making it a potent insecticide. Oligomycin inhibits ATP synthase, also slowing flow of the electron transport chain. Fructose 2,6-biphosphate affects the activity of enzymes regulating glycolysis and gluconeogenesis. Dinitrophenol dissipates the proton gradient across mitochondrial membranes, and shuttles protons across them, inhibiting ATP production. 

Example Question #33 : Electron Transport And Oxidative Phosphorylation

Suppose that a scientist is simultaneously measuring both the amount of oxygen and the amount of glucose that is being used by cells. If a chemical were added that inhibited the electron transport chain, what would be expected to happen to the consumption of oxygen and glucose?

Possible Answers:

Oxygen consumption decreases while glucose consumption increases

Both oxygen and glucose consumption decrease

Both oxygen and consumption will remain unchanged

Oxygen consumption increases while glucose consumption decreases

Both oxygen and glucose consumption increase

Correct answer:

Oxygen consumption decreases while glucose consumption increases

Explanation:

Aerobic respiration is a process that utilizes the electron transport chain in order to oxidize glucose into energy. If a chemical were added that inhibited the electron transport chain, the cell would no longer be able to fully oxidize glucose. Therefore, oxygen consumption will decrease. Furthermore, since the cell is now in a situation in which it is not able to make as much energy per glucose molecule as before, it will need to increase its consumption of glucose in order to generate enough energy through anaerobic respiration alone.

Example Question #34 : Electron Transport And Oxidative Phosphorylation

ATP synthase can be inhibited exclusively by __________.

Possible Answers:

Rotenone

Cyanide 

Antimycin

Oligomycin

Correct answer:

Oligomycin

Explanation:

Oligomycin is an antibiotic that inhibits ATP synthase. It works by binding to the stalk of ATP synthase. This prevents proton re-entry into the mitochondrial matrix. This results in a halt of the proton motive force that ATP synthase uses to created ATP from one unit of ADP and one unit of inorganic phosphate. Rotenone is a pesticide and fish poison that inhibits NADH dehydrogenase in complex I causing the levels of NADH to increase. This results in a halt of the electron transport chain. Antimycin is a fungal antibiotic that inhibits complex III of the electron transport chain. Antimycin prevents the transfer of electrons through the cytochrome b-c complex. Cyanide is a gas that inhibits complex IV of the electron transport chain. Cyanide combines with cytochrome oxidase and prevents the transfer of electrons to oxygen.

Example Question #35 : Electron Transport And Oxidative Phosphorylation

Complex III can be inhibited exclusively by __________.

Possible Answers:

Oligomycin

Rotenone

Cyanide

Antimycin

Correct answer:

Antimycin

Explanation:

Antimycin is a fungal antibiotic that inhibits complex III of the electron transport chain. Antimycin prevents the transfer of electrons through the cytochrome b-c complex. Oligomycin is an antibiotic that inhibits ATP synthase. It works by binding to the stalk of ATP synthase. This prevents proton re-entry into the inner mitochondrial matrix. This results in a halt of the proton motive force that ATP synthase uses to created ATP from one unit of ADP and one unit of inorganic phosphate. Rotenone is a pesticide and fish poison that inhibits NADH dehydrogenase in complex I causing the levels of NADH to increase. This results in a halt of the electron transport chain. Cyanide is a gas that inhibits complex IV of the electron transport chain. Cyanide combines with cytochrome oxidase and prevents the transfer of electrons to oxygen.

Example Question #36 : Electron Transport And Oxidative Phosphorylation

Complex I can be inhibited exclusively by __________.

Possible Answers:

Oligomycin

Cyanide

Antimycin

Rotenone

Correct answer:

Rotenone

Explanation:

Rotenone is a pesticide and fish poison that inhibits NADH dehydrogenase in complex I causing the levels of NADH to increase. This results in a halt of the electron transport chain. Oligomycin is an antibiotic that inhibits ATP synthase. It works by binding to the stalk of ATP synthase. This prevents proton re-entry into the mitochondrial matrix. This results in a halt of the proton motive force that ATP synthase uses to created ATP from one unit of ADP and one unit of inorganic phosphate. Antimycin is a fungal antibiotic that inhibits complex III of the electron transport chain. Antimycin prevents the transfer of electrons through the cytochrome b-c complex. Cyanide is a gas that inhibits complex IV of the electron transport chain. Cyanide combines with cytochrome oxidase and prevents the transfer of electrons to oxygen.

Example Question #37 : Electron Transport And Oxidative Phosphorylation

Complex IV can be inhibited exclusively by __________.

Possible Answers:

Cyanide

Antimycin

Oligomycin

Rotenone

Correct answer:

Cyanide

Explanation:

Cyanide is a gas that inhibits complex IV of the electron transport chain. Cyanide combines with cytochrome oxidase and prevents the transfer of electrons to oxygen. Antimycin is a fungal antibiotic that inhibits complex III of the electron transport chain. Antimycin prevents the transfer of electrons through the cytochrome b-c complex. Oligomycin is an antibiotic that inhibits ATP synthase. It works by binding to the stalk of ATP synthase. This prevents proton re-entry into the mitochondrial matrix. This results in a halt of the proton motive force that ATP synthase uses to created ATP from one unit of ADP and one unit of inorganic phosphate. Rotenone is a pesticide and fish poison that inhibits NADH dehydrogenase in complex I causing the levels of NADH to increase. This results in a halt of the electron transport chain.

Example Question #38 : Electron Transport And Oxidative Phosphorylation

Which of the following is a function of coenzyme Q10 (CoQ10) during the electron transport chain (ETC)?

Possible Answers:

Oxidizes enzyme complex II

Oxidizes enzyme complex III

Donates electrons to FADH

Reduces enzyme complex I

The ultimate acceptor of electrons 

Correct answer:

Oxidizes enzyme complex II

Explanation:

CoQ10 is produced in the liver and oxidizes enzyme complex II. It is subsequently oxidized by enzyme complex III in the ETC. Oxygen is the final acceptor of electrons in the ETC.

Example Question #39 : Electron Transport And Oxidative Phosphorylation

Oxygen is known as the "terminal electron receptor" in the electron transport chain. Suppose an organism lacks the ability to breathe in oxygen.

What is the most likely effect an oxygen deficit would have on the electron transport chain in mitochondria?

Possible Answers:

The oxygen would not be able to interact with ATP synthase and thus ATP production would halt, however, the electron transport chain would continue to function normally otherwise.

Without a terminal electron acceptor, the electrons of  and  would have nowhere to be released, and all of the enzyme complexes involved with the electron transport chain would be "saturated" with electrons and the entire electron transport chain would cease to function, halting production of ATP.

The mitochondria would synthesize new complexes for the electron transport chain and ATP production would continue.

A mitochondria would use an alternative terminal electron receptor such as nitrogen or carbon dioxide, the electron transport chain would continue to function.

Nothing would happen, the electron transport chain would function normally.

Correct answer:

Without a terminal electron acceptor, the electrons of  and  would have nowhere to be released, and all of the enzyme complexes involved with the electron transport chain would be "saturated" with electrons and the entire electron transport chain would cease to function, halting production of ATP.

Explanation:

Without a terminal electron acceptor, the electrons of  and  would have nowhere to be released, all of the complexes would be "backed up" as each complex would not be able to pass off its electrons to the next complex. ATP production would come to a standstill.

Without oxygen to receive the electrons, the entire flow of the electron transportation chain halts, as well as ATP production. It is the continuous flow of electrons through the ETC complexes that allows a mitochondria to harness the energy of the electrons that  and  donate. This energy is used to pump protons across the intermembrane space of a mitochondria. The re-entry of these protons through ATP synthase is what drives the production of ATP.

In short, no electron flow means no proton pumps and no re-entry of those protons through ATP synthase. A cell could potentially resort to glycolysis to produce ATP, and can regenerate  or  using anaerobic fermentation such as alcohol fermentation of lactic acid fermentation.

Example Question #40 : Electron Transport And Oxidative Phosphorylation

To which component of the electron transport chain does cyanide bind?

Possible Answers:

Cyanide binds the electron transport chain at the level of complex IV

Cyanide binds the electron transport chain at the level of coenzyme Q

Cyanide binds ATP synthase

Cyanide binds the electron transport chain at the level of complex I

Cyanide binds the electron transport chain at the level of complex III

Correct answer:

Cyanide binds the electron transport chain at the level of complex IV

Explanation:

The electron transport chain passes electrons thru its main components: complex I (NADH dehydrogenase), coenzyme Q, complex III, cytochrome C, and complex IV. Complex IV is the cytochrome oxidase complex and it is inhibited by cyanide, carbon monoxide and azide. Cyanide binds irreversibly to complex IV preventing electron transfer.

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