Question 1

Which of the following regarding redox reactions is NOT correct?

Accepted Answer

For redox reactions with negative standard reduction potentials, the standard free energy change is positive, not negative.

Question 2

Which of the following cytochromes receives the electron transferred from UQH₂ to the Rieske protein?

Accepted Answer

Cytochrome c1 receives the electron transferred from the Rieske protein in the electron transport chain within the mitochondrial inner membrane.

Question 3

Which of the following classifies the phosphorylation of ADP that is NADH-dependent?

Accepted Answer

Substrate-level phosphorylation is the process of phosphorylating ADP to ATP using the energy released from the breakdown of a high-energy compound. In this case, the high-energy compound is NADH, which is oxidized to NAD+ and releases energy that is used to phosphorylate ADP to ATP.

Question 4

Which of the following is a mobile electron carrier?

Accepted Answer

Ubiquinone (UQ), also known as Coenzyme Q10, is a mobile electron carrier that is found in the inner mitochondrial membrane. It accepts electrons from Complexes I and II and transfers them to Complex III.

Question 5

Which of the following components is a 2-electron donor?

Accepted Answer

NADH is a 2-electron donor, as it carries two electrons and a proton (H+) during redox reactions. FAD, Fe-S, and cyt c are all one-electron donors.

Question 6

Which of the following metabolic pathways is NOT linked to the electron-transport chain through Complex I,which accepts electrons from NADH?

Accepted Answer

Gluconeogenesis is not linked to the electron-transport chain through complex I, as it involves the conversion of non-carbohydrate substrates such as amino acids and lactate into glucose through a series of enzymatic reactions that do not involve electron transfer to complex I. Glycolysis, TCA cycle, and fatty acid oxidation all feed electrons into complex I through NADH.

Question 7

Which of the following components part of Complex I?

Accepted Answer

Complex I, also known as NADH:ubiquinone oxidoreductase, contains 4Fe-4S clusters as part of its structure.

Question 8

NADH is a strong reducing agent.What kind of reduction potential does it possess?

Accepted Answer

NADH is a strong reducing agent because it can donate electrons to other molecules. This means it has a large negative reduction potential, as it has a strong tendency to give away electrons.

Question 9

Which of the following is a characteristic of inner mitochondrial membranes?

Accepted Answer

Inner mitochondrial membranes have a characteristic folding pattern that creates cristae, increasing their surface area for energy production.

Question 10

Which of the following is a property of coenzyme Q?

Accepted Answer

Coenzyme Q, also known as ubiquinone, has three oxidation states (fully reduced, semiquinone, and fully oxidized), which allow it to accept and donate electrons during oxidative phosphorylation.

Question 11

Which of the following is the source for the energy that drives ATP synthesis?

Accepted Answer

The source of energy that drives ATP synthesis is the proton gradient - this is established by the electron transport chain in the mitochondria. As protons are pumped across the inner mitochondrial membrane, they create a gradient which can be harvested to drive the synthesis of ATP. NAD⁺ and FAD are coenzymes involved in the electron transport chain, but they are not the direct source of energy for ATP synthesis. The electron gradient is also involved in the electron transport chain and indirectly contributes to the establishment of the proton gradient, but it is not the direct source of energy. Molecular oxygen is the final electron acceptor in the electron transport chain, but it is not the direct source of energy for ATP synthesis.

Question 12

Which of the following takes place in the Q cycle?

Accepted Answer

In the Q cycle, one UQH₂ (ubiquinol) is oxidized, and one of the resulting ubiquinones is returned to the pool, while the other is reduced back to ubiquinol.

Question 13

Which of the following complexes reduces molecular oxygen?

Accepted Answer

Complex IV, also known as cytochrome c oxidase, is responsible for reducing molecular oxygen to water during oxidative phosphorylation.

Question 14

Which of the following is the common product produced by Complex I and Complex II?

Accepted Answer

Both Complex I and Complex II transfer electrons to coenzyme Q (CoQ), which becomes reduced (QH2) and can then transfer those electrons to Complex III in the electron transport chain. None of the other options (FAD, NAD⁺, reduced O₂) are products of Complex I or II.

Question 15

Which of the following reaction classifications has a standard reduction potential that is positive under standard conditions?

Accepted Answer

A reaction with a standard reduction potential that is positive under standard conditions is a spontaneous reaction. This means that the reaction will occur without the need for input of energy and will proceed in the direction of the reduction half-reaction with the more positive reduction potential.

Question 16

Which of the following enzymes is NOT a flavoprotein?

Accepted Answer

Coenzyme Q-cytochrome c oxidoreductase, also known as Complex III in the electron transport chain, is not classified as a flavoprotein. Flavoproteins are proteins that contain a nucleic acid derivative of riboflavin: the flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN). NADH-CoQ reductase (Complex I), succinate dehydrogenase (Complex II), and fatty acyl-CoA dehydrogenase are examples of enzymes that use FAD or FMN as a cofactor, making them flavoproteins. Complex III, however, does not use FAD or FMN as a cofactor, distinguishing it from the others listed.

Question 17

Which of the following is need for the spontaneity of a redox reaction?

Accepted Answer

The answer of Which of the following is need for...

Question 18

Which of the following correct regarding redox couples is NOT?

Accepted Answer

A redox couple actually consists of a reduced species and its corresponding oxidized form. It is not composed of a substance being oxidized and the substance oxidizing it. The other options (A, B, and D) are correct statements regarding redox couples.

Question 19

Which of the following components is NOT membrane bound?

Accepted Answer

Cytochrome c is a soluble protein and is not membrane-bound, unlike the other components listed which are all integral membrane proteins.

Question 20

Which of the following resides in the mitochondria?

Accepted Answer

The electron transport complexes are responsible for generating ATP via oxidative phosphorylation and are found in the inner membrane of the mitochondria. Enzymes for glycolysis are found in the cytoplasm, adenylate cyclase is found in the plasma membrane, and the pentose phosphate pathway occurs in both the cytoplasm and the mitochondria.

Quiz 19: Electron Transport and Oxidative Phosphorylation