Oxidative Phosphorylation and ETC Complexes

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Questions and Answers

Which of the following statements accurately describes the role of oxidoreductase in the electron transport chain (ETC)?

  • It directly facilitates the movement of protons across the inner mitochondrial membrane.
  • It functions as a structural component within the protein to encourage electron movement.
  • It acts as a catalyst for both oxidation and reduction reactions necessary for electron transfer. (correct)
  • It solely provides the necessary coenzymes for electron attachment without affecting redox reactions.

In complex I of the electron transport chain, what is the correct sequence of electron transfer among its components?

  • NADH -> FMN -> Fe-S -> CoQ (correct)
  • NADH -> Fe-S -> FMN -> CoQ
  • NADH -> FMN -> CoQ -> Fe-S
  • NADH -> CoQ -> FMN -> Fe-S

Which of the following is a key distinction between electron transport via NADH and FADH2 in the electron transport chain?

  • NADH transfers electrons directly to complex II, while FADH2 starts at complex I.
  • NADH requires ubiquinone for electron transfer, while FADH2 uses cytochrome C.
  • NADH generates fewer ATP molecules compared to FADH2 due to bypassing complex I.
  • NADH initiates electron transport at complex I, whereas FADH2 enters at complex II. (correct)

What is the primary role of ubiquinone (CoQ) in the electron transport chain?

<p>To serve as a mobile carrier, transporting electrons between complexes. (D)</p> Signup and view all the answers

During the Q cycle in complex III, what is the immediate fate of the two electrons released from QH2?

<p>One electron moves to cytochrome c1, and the other moves downward to a heme group in cytochrome b. (A)</p> Signup and view all the answers

Which of the following best describes the role of cytochrome c in the electron transport chain?

<p>It is a mobile carrier that transfers electrons between Complex III and Complex IV. (B)</p> Signup and view all the answers

What is the significance of Complex II not spanning the mitochondrial membrane, unlike Complexes I, III, and IV?

<p>The energy released is insufficient to pump protons across the membrane. (D)</p> Signup and view all the answers

What is the final electron acceptor in the electron transport chain, and what product does it form upon accepting electrons?

<p>Oxygen; forms water (H2O). (B)</p> Signup and view all the answers

In Complex IV, how many electrons are ultimately required to fully reduce one molecule of dioxygen (O2)?

<p>Four electrons (B)</p> Signup and view all the answers

What is the significance of the iron atom's oxidation state in cytochrome c during electron transport?

<p>It enables cytochrome c to either gain or lose one electron. (B)</p> Signup and view all the answers

If an inhibitor blocks Complex IV of the electron transport chain, what would be the expected state of the components upstream of the block?

<p>All components upstream would become reduced. (C)</p> Signup and view all the answers

What is the approximate ATP yield from the passage of two electrons through the electron transport chain when the electron source is NADH?

<p>2.5 ATP (A)</p> Signup and view all the answers

Why is the actual ATP yield from the electron transport chain less than the theoretical yield?

<p>Because the movement of molecules across the inner mitochondrial membrane consumes energy. (D)</p> Signup and view all the answers

Under anaerobic conditions, the electron transport chain is unable to operate. What initial change would be observed?

<p>All complexes will become reduced. (A)</p> Signup and view all the answers

A researcher introduces an inhibitor to Complex I. Which of the following would accurately describe the state of the electron carriers?

<p>Carriers before Complex I reduced; Carriers after Complex I oxidized. (C)</p> Signup and view all the answers

Flashcards

Oxidoreductase

A compound that transfers electrons by oxidizing one substance and reducing another.

Complex I

Accepts electrons from NADH and donates electrons to CoQ. Contains FMN and iron-sulfur clusters.

Complex II

Contains succinate and iron-sulfur clusters. Accepts electrons from succinate.

Complex III

Contains cytochrome C1, cytochrome B, and iron-sulfur clusters.

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Complex IV

Contains copper heme a and copper heme a3. Transfers electrons to oxygen.

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FMN

Tightly bound; similar to FAD but lacks adenine.

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Fe-S clusters

Geometric structures that transfer one electron at a time through iron.

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Succinate dehydrogenase

Part of Krebs cycle; converts succinate to fumarate and produces FADH2.

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CoQ (Ubiquinone)

A lipid-soluble electron carrier transporting electrons between complexes.

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Q cycle

Describes the stoichiometry of electrons entering and exiting Complex III.

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Determining ETC arrangement

Measures the standard reduction potential of all molecules in the ETC.

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Methemoglobin

The hemoglobin that contains Heme group that contains oxidized iron rather than reduced iron

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Proton pumping

Energy released during electron transfer pumps H+ across the inner mitochondrial membrane

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Efficiency of ETC

The amount of energy from glucose oxidation converted to ATP.

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Inhibitors of ETC

Prevents electron transfer, halting ATP production.

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Study Notes

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