Question 1

Which complex of the electron transport chain does NOT contain an iron-sulfur cluster?

Accepted Answer

Complex IV, also known as cytochrome c oxidase, does not contain an iron-sulfur cluster. It primarily contains copper centers and heme groups that are involved in the transfer of electrons to oxygen, the final electron acceptor.

Question 2

Complex IV of the electron transport chain oxidizes ____,reduces ____,and ____ protons in the process.

Accepted Answer

D

Question 3

To calculate the DG of a redox reaction,you need:

Accepted Answer

To calculate the DG of a redox reaction, all of the given factors are needed. The reduction potential (E°) of the half reactions gives information about the tendency of the species to gain or lose electrons. The Faraday constant helps to convert the number of electrons involved in the transfer into moles. Both of these, along with the standard conditions, are used to calculate the standard DG°.

Question 4

How many electrons are required for the complete reduction of one molecule of oxygen gas?

Accepted Answer

The complete reduction of one molecule of oxygen gas (O2) to water (H2O) requires four electrons, according to the equation: O2 + 4e- + 4H+ → 2H2O.

Question 5

Which of the following components of the electron transport chain can only participate in one-electron transfers?

Accepted Answer

Cytochrome C can only participate in one-electron transfers, while the others listed can participate in both one- and two-electron transfers.

Question 6

The Q cycle refers to flow of electrons from

Accepted Answer

The Q cycle is the transfer of electrons from coenzyme Q (also known as ubiquinone) to cytochrome c via Complex III in the electron transport chain. This cycle generates the proton gradient used to produce ATP. Options A, B, and D do not accurately describe the Q cycle.

Question 7

The ultimate electron acceptor in the electron transport chain is

Accepted Answer

Oxygen is the final electron acceptor in the electron transport chain, which ultimately leads to the production of ATP through oxidative phosphorylation. This occurs in the inner mitochondrial membrane of eukaryotic cells or the plasma membrane of prokaryotic cells.

Question 8

Which of the following is not a part of the electron transport chain?

Accepted Answer

Coenzyme A is involved in the citric acid cycle, but not in the electron transport chain.

Question 9

The final reduced species in the electron transport chain is

Accepted Answer

The final reduced species in the electron transport chain is H2O.

Question 10

Which of the following statements concerning E° for an electron-transfer reaction is false?

Accepted Answer

E° is not measured by comparison with the partial pressure of oxygen in the bloodstream. It is typically measured by comparison with a standard hydrogen electrode or other reference electrode. Choice B is true. E° is related to DG° by the equation: DG° = -nF E°, where n is the number of electrons transferred and F is the Faraday constant. Choice C is true. Choice D is false; E° can be determined for electron-transfer reactions involving coenzyme Q.

Question 11

Which of the following is not true?

Accepted Answer

The synthesis of ATP is indirectly linked to the oxidation of NADH and FADH2, as the electron transport chain generates a proton gradient that ultimately drives ATP synthesis. However, the oxidation of NADH and FADH2 does not directly produce ATP.

Question 12

When mitochondria are actively carrying out aerobic respiration

Accepted Answer

During aerobic respiration, protons (H+) are pumped from the matrix into the intermembrane space, creating a proton gradient. This results in a higher concentration of H+ in the intermembrane space, making it more acidic (lower pH) compared to the matrix, which becomes more alkaline (higher pH).

Question 13

Reduction potentials (E°) are measured by reading a voltmeter,which measures the electron flow between two reaction chambers.

Accepted Answer

Reduction potentials are indeed measured by reading a voltmeter, which measures the potential difference between two electrodes placed in different reaction chambers. This potential difference is then used to calculate the reduction potential of the half-reaction occurring at each electrode.

Question 14

Complex III of the electron transport chain oxidizes ____,reduces ____,and ____ protons in the process.

Accepted Answer

Complex III of the electron transport chain oxidizes coenzyme Q (ubiquinone), reduces cytochrome c, and pumps protons across the mitochondrial membrane, contributing to the proton gradient used for ATP synthesis.

Question 15

Complex II of the electron transport chain oxidizes ____,reduces ____,and ____ protons in the process.

Accepted Answer

Complex II oxidizes FADH2 to FAD, reduces coenzyme Q (ubiquinone) to ubiquinol, and does not pump protons across the mitochondrial membrane.

Question 16

The reference reaction for determining reduction potentials (E° = 0) is the reduction of

Accepted Answer

The standard hydrogen electrode (SHE) is the reference electrode for determining standard reduction potentials, where H⁺ ions are reduced to H₂ gas, and it is assigned a potential of 0 volts.

Question 17

The pH of the mitochondrial matrix is ____ the pH of the intermembrane space.

Accepted Answer

The pH of the mitochondrial matrix is typically around 7.4, which is higher than the pH of the intermembrane space, which is typically around 6.

Question 18

Which of the following terms describes ATP synthesis in mitochondria?

Accepted Answer

Oxidative phosphorylation is the process by which ATP is synthesized in mitochondria from the energy released by the oxidation of nutrients, mainly glucose and fatty acids. This process involves electron transport through the inner mitochondrial membrane and ATP synthase, which synthesizes ATP from ADP and Pi. Substrate-level phosphorylation refers to ATP synthesis through the transfer of a phosphate group from a substrate molecule to ADP, but this process occurs mainly in the cytosol during glycolysis, and it is not the primary mechanism of ATP synthesis in mitochondria. Photophosphorylation is the process by which ATP is synthesized in chloroplasts during photosynthesis, and it involves the absorption of light energy by pigments and the transfer of electrons through a series of electron carriers. This process is not relevant to ATP synthesis in mitochondria.

Question 19

Complex I of the electron transport chain oxidizes ____,reduces ____,and ____ protons in the process.

Accepted Answer

Complex I of the electron transport chain oxidizes NADH, reduces coenzyme Q, and pumps protons in the process.

Question 20

Which of the following is an advantage of using multiple steps in electron transport?

Accepted Answer

Multiple steps in electron transport allow for more energy to be captured to synthesize ATP. This is because each step releases a smaller amount of energy, which can be used more efficiently to produce ATP through ATP synthase. Options A, B, and D are incorrect because they suggest that multiple steps either result in higher energy release or more heat generation, which is not necessarily true. Option E is incorrect because it suggests that all of the statements are advantages of using multiple steps, which is also not entirely true.

Quiz 20: Electron Transport and Oxidative Phosphorylation