Metabolic: lecture 24
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Questions and Answers

What is the standard reduction potential (E'˚) for the half-reaction involving NAD+ to NADH?

  • -0.32 (correct)
  • -0.324
  • -0.414
  • 0.045

    • Which complex in the electron transport chain actively transports protons across the membrane?

  • 2
  • 1 (correct)
  • 3
  • 4 (correct)

    • What is the overall change in Gibbs free energy (ΔG'°) when NADH is oxidized to NAD+ in the presence of oxygen?

  • -22
  • -22000
  • -220 (correct)
  • -2200

    • What is the standard reduction potential (E'˚) for the half-reaction of oxygen reduction to water?

    <p>0.817 (A)</p> Signup and view all the answers

    Which of the following processes contributes to the proton-motive force established by the electron transport chain?

    <p>1.3 (A), 1.1 (C)</p> Signup and view all the answers

    What is the E'˚ value for the reduction of cytochrome a3 (Fe3+) to cytochrome a3 (Fe2+)?

    <p>0.35 (B)</p> Signup and view all the answers

    What is the role of Coenzyme Q (CoQ) in the electron transport chain?

    <p>1.4 (A), 1.5 (C)</p> Signup and view all the answers

    Which compound has the lowest standard reduction potential in the given reactions?

    <p>200 (B)</p> Signup and view all the answers

    What is the primary function of Complex III in the electron transport chain?

    <p>Oxidizes QH2 and reduces cytochrome c. (D)</p> Signup and view all the answers

    How many protons are transported to the intermembrane space for every two electrons transferred through Complex III?

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

    What distinguishes cytochrome c from ubiquinone as an electron carrier?

    <p>Ubiquinone is mobile within the membrane, while cytochrome c is soluble in the intermembrane space. (D)</p> Signup and view all the answers

    Which statement correctly describes the role of Complex IV in the electron transport chain?

    <p>It reduces molecular oxygen to form water. (A)</p> Signup and view all the answers

    During the Q cycle, how do additional protons get picked up from the matrix?

    <p>Through oxidation of QH2. (A)</p> Signup and view all the answers

    What is the composition of Complex IV (Cytochrome Oxidase)?

    <p>It includes copper ions and two heme groups. (B)</p> Signup and view all the answers

    Which of the following statements about heme iron is correct?

    <p>Heme iron can exist in both ferric (Fe3+) and ferrous (Fe2+) states. (A)</p> Signup and view all the answers

    In the overall reaction summarized for Complex I, what are the main products formed?

    <p>NAD+ and protons. (D)</p> Signup and view all the answers

    What is the primary function of Coenzyme Q in the mitochondrial electron transport chain?

    <p>It transports electrons from Complex I and II to Complex III. (C)</p> Signup and view all the answers

    Which complex of the mitochondrial electron transport chain is primarily responsible for pumping protons from the mitochondrial matrix to the intermembrane space?

    <p>Complex I (B)</p> Signup and view all the answers

    What occurs during the reduction of Q in the mitochondrial electron transport chain?

    <p>NADH is oxidized to NAD+. (B)</p> Signup and view all the answers

    Which statement best describes the role of succinate dehydrogenase (Complex II) in the electron transport chain?

    <p>It both converts succinate to fumarate and donates electrons to ubiquinone. (C)</p> Signup and view all the answers

    How many protons are suggested to be transported per molecule of NADH during the process of electron transfer to ubiquinone?

    <p>4 protons (C)</p> Signup and view all the answers

    What is the function of FMN (flavin mononucleotide) in Complex I of the electron transport chain?

    <p>It accepts electrons from NADH. (C)</p> Signup and view all the answers

    In the context of proton transport, what role do the 'proton wires' play in Complex I?

    <p>They facilitate the transport of protons across the membrane. (A)</p> Signup and view all the answers

    What would be the end products when NADH donates electrons to ubiquinone, according to the reaction presented?

    <p>NAD+, QH2, and 4 H+ in the matrix (B)</p> Signup and view all the answers

    Flashcards

    Mitochondrial Electron Transport

    A series of protein complexes in the inner mitochondrial membrane that transfer electrons and pump protons to generate ATP.

    Coenzyme Q (Ubiquinone)

    A mobile electron carrier that transports electrons from complexes I and II to complex III in the electron transport chain.

    Complex I (NADH:Ubiquinone Oxidoreductase)

    A large enzyme complex that accepts electrons from NADH and passes them to ubiquinone, pumping protons into the intermembrane space.

    Complex II (Succinate Dehydrogenase)

    A complex that participates in the Citric Acid Cycle (CAC) and also transfers electrons from succinate to ubiquinone.

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    Electron Transport Chain

    A sequence of protein complexes that transfer electrons from electron donors to electron acceptors via redox reactions, generating a proton gradient.

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    Proton Gradient

    A difference in proton concentration across a membrane that stores energy for ATP synthesis.

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    ATP Synthesis

    The process of producing ATP using the energy stored in the proton gradient across the inner mitochondrial membrane.

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    Reduced Coenzyme Q (QH2)

    Coenzyme Q (Ubiquinone) after receiving two electrons, becoming reduced.

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    Complex III (Ubiquinone:Cytochrome c Oxidoreductase)

    A protein complex in the electron transport chain that transfers electrons from ubiquinol (QH2) to cytochrome c, and pumps protons across the membrane.

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    Q cycle

    A process in Complex III that uses two electrons from QH2 to reduce two cytochrome c molecules, and moves four protons to the intermembrane space.

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    Cytochrome c

    A small protein that carries electrons between Complex III and Complex IV in the electron transport chain.

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    Ubiquinone

    A lipid-soluble electron carrier that moves through the membrane, accepting electrons at Complex I or II.

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    Complex IV (Cytochrome Oxidase)

    The last complex in the electron transport chain that uses electrons to reduce oxygen to water and pumps protons.

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    Electron Transport Chain (ETC)

    A series of protein complexes that transfer electrons from electron donors to electron acceptors, driving proton pumping across the membrane.

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    Proton Pumping

    Movement of protons (H+) across the inner mitochondrial membrane, creating a proton gradient used to generate ATP.

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    Oxygen Reduction

    The process where oxygen gains electrons (H+) and forms water during the final stage of the electron transport chain in Complex IV.

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    Standard Reduction Potential (E'˚)

    A measure of the tendency of a molecule to gain electrons and be reduced. Higher values indicate a stronger tendency to receive electrons and be reduced.

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    Respiratory Chain Carriers

    Molecules within the electron transport chain that accept and transfer electrons, allowing for energy release in the process

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    Proton-Motive Force

    The electrochemical gradient of protons (H+) across a membrane, driven by electron transport.

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    NADH

    A key electron carrier in cellular respiration.

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    Complex I

    A protein complex in the electron transport chain that actively transports protons.

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    Chemiosmotic Model

    Theory of ATP synthesis linked to the proton gradient created by electron transport.

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    Study Notes

    Mitochondrial Electron Transport

    • Mitochondrial electron transport (MET) involves four inner mitochondrial membrane complexes and two mobile electron carriers (Coenzyme Q and cytochrome c)
    • All components are embedded in the membrane.
    • The process involves a large positive change in free energy. The free energy relative to oxygen is measured in kJ/mol

    Complexes and Electron Carriers

    • NADH dehydrogenase (Complex I): Transfers electrons from NADH to Ubiquinone (Coenzyme Q). Accompanies a transfer of protons from the matrix to intermembrane space. About 4 protons are transported for each NADH reacted.

    • Succinate dehydrogenase (Complex II): Converts succinate to fumarate. Captures and donates electrons to the electron transport chain, generating ATP. Does not transport protons across the inner mitochondrial membrane.

    • Ubiquinone:cytochrome c oxidoreductase (Complex III): Uses two electrons from QH2 to reduce two molecules of cytochrome c. Translocates four additional protons to the intermembrane space. Clearance of electrons from reduced quinones creates a Q-cycle.

    • Cytochrome c oxidase (Complex IV): Transfers four electrons from cytochrome c to oxygen. Two ions (CuA & CuB) are involved in accepting electrons and bonding to oxygen, forming water. Four protons are picked up from the matrix. Two additional protons are transported across the membrane.

    The Q Cycle

    • The Q cycle is a process where electrons from QH2 are transported to cytochrome c and additional protons are pumped into the intermembrane space. Two QH2 molecules are oxidized releasing protons into the intermembrane space. A single molecule of Q becomes re-reduced, transferring 4 protons (for two electrons)
    • Four protons are transported across the membrane per two electrons that reach cytochrome c.
    • Two of the four protons come from QH2.
    • Two molecules of QH₂ become oxidized, releasing protons into the intermembrane space. One molecule of Q becomes re-reduced, resulting in a net transfer of four protons per reduced coenzyme Q

    Cytochrome C

    • Cytochrome c is a heme-containing protein.
    • The heme iron can exist in ferric (Fe3+, oxidized) or ferrous (Fe2+, reduced) forms.
    • It carries a single electron from Complex III to Complex IV.
    • Ubiquinone moves through the membrane while Cytochrome c moves through the intermembrane space.

    Cytochrome Oxidase (Complex IV)

    • Cytochrome oxidase is a membrane protein with 13 subunits.
    • It contains two heme groups and two copper ions (CuA & CuB).
    • It transfers four electrons from cytochrome c to oxygen, forming two water molecules.
    • Four protons are picked up from the matrix and two additional protons are transported across the membrane.

    Proton Motive Force (PMF)

    • Proteins in the ETC create an electrochemical proton gradient across the membrane.
    • Three methods accomplish this:
      • Actively transporting protons across the membrane (Complexes I, III, and IV)
      • Chemically removing protons from the matrix during the reduction of CoQ and oxygen.
      • Releasing protons into the intermembrane space during oxidation of QH2

    Chemiosmotic Model for ATP Synthesis

    • Electron transport sets up a proton-motive force.
    • The energy of the proton-motive force drives ATP synthesis.

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    Description

    This quiz covers the fundamental components and processes involved in mitochondrial electron transport. It focuses on the roles of electron carriers, complexes, and energy changes associated with this vital biochemical pathway. Test your understanding of how electrons are transferred and protons are pumped during cellular respiration.

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