Biochemistry Chapter on Electron Transport Chain
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Questions and Answers

What is the primary role of the electricity generated by the electron transport chain (ETC)?

  • Directly synthesize ATP within the mitochondrial matrix.
  • Power the movement of protons across the inner mitochondrial membrane, creating a proton gradient. (correct)
  • Facilitate the oxidation of NADH and FADH2.
  • Bind irreversibly to cytochrome a/a3, preventing electron transfer to oxygen.

    • Which complexes within the electron transport chain (ETC) are directly involved in translocating protons from the mitochondrial matrix to the intermembrane space?

  • Complex I, Complex III, and Complex IV (NADH dehydrogenase, cytochrome b/c1, and cytochrome a/a3). (correct)
  • Complex II, Complex III, and Complex IV.
  • Complex II and Complex V (ATP synthase).
  • Only Complex IV (cytochrome a/a3).

    • How does the F1-F0-ATP synthase complex utilize the proton gradient generated by the electron transport chain (ETC)?

  • It uses the energy from proton flow to phosphorylate ADP, forming ATP. (correct)
  • It binds cyanide, preventing electron transfer.
  • It transports electrons to oxygen, completing the ETC.
  • It directly oxidizes NADH and FADH2.

    • Approximately how many ATP molecules can be generated from the oxidation of one molecule of FADH2 in the electron transport chain (ETC)?

    <p>Approximately 2 ATP. (D)</p> Signup and view all the answers

    What is the primary mechanism by which cyanide inhibits the electron transport chain (ETC)?

    <p>By binding irreversibly to cytochrome a/a3, preventing electron transfer to oxygen. (C)</p> Signup and view all the answers

    What are the effects from inhibiting steps in the electron transport chain (ETC) that are coupled to oxidative phosphorylation?

    <p>Decreased oxygen consumption, increased intracellular NADH/NAD+ and FADH2/FAD ratios, and decreased ATP. (A)</p> Signup and view all the answers

    Carbon monoxide (CO) poisoning shares some similar effects to cyanide poisoning. What is a key difference in their mechanisms of action?

    <p>CO also binds to hemoglobin, displacing oxygen, while cyanide does not. (C)</p> Signup and view all the answers

    What causes the cherry-red color of the lips and cheeks observed in individuals with carbon monoxide poisoning?

    <p>Decreased oxygen binding to hemoglobin and a shift in the color of blood. (D)</p> Signup and view all the answers

    What is the primary effect of uncouplers on ATP synthesis?

    <p>Decreased ATP synthesis (B)</p> Signup and view all the answers

    Which of the following substances is NOT considered a natural uncoupler?

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

    How do bacterial toxins such as Pneumolysin affect mitochondrial function?

    <p>They disrupt mitochondrial membranes (D)</p> Signup and view all the answers

    What role does brown fat play in infants when they are cold?

    <p>Burns body fat to generate heat (A)</p> Signup and view all the answers

    What is the outcome when the electron transport chain (ETC) rate increases without ATP synthesis?

    <p>Release of energy as heat (D)</p> Signup and view all the answers

    Which of the following statements about the NADH shuttle system is true?

    <p>It is essential for glucose-induced mitochondrial activation (C)</p> Signup and view all the answers

    What effect do uncouplers have on oxygen consumption?

    <p>Increased oxygen consumption (A)</p> Signup and view all the answers

    What is the impact of increased membrane permeability to protons on ATP synthesis?

    <p>Reduces ATP synthesis efficiency (C)</p> Signup and view all the answers

    What is the primary function of the citric acid cycle?

    <p>Oxidation of acetyl-CoA to carbon dioxide, conserving energy as NADH, FADH2, and GTP. (B)</p> Signup and view all the answers

    Why does the citric acid cycle not occur anaerobically?

    <p>NADH and FADH2 accumulate if oxygen is unavailable in the electron transport chain, inhibiting the cycle. (C)</p> Signup and view all the answers

    The citric acid cycle is central to the oxidation of which of the following fuel sources?

    <p>Any fuel that yields acetyl-CoA, including glucose, fatty acids, and ketogenic amino acids (A)</p> Signup and view all the answers

    What exerts control over the citric acid cycle?

    <p>The energy status of the cell (A)</p> Signup and view all the answers

    Which enzyme is a major control point in the TCA cycle, inhibited by NADH and ATP, and activated by ADP?

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

    Which of the following is required by α-Ketoglutarate dehydrogenase complex to function?

    <p>Thiamine, lipoic acid, CoA, FAD, and NAD (D)</p> Signup and view all the answers

    A deficiency in which vitamin would directly impair the oxidation of acetyl-CoA in the citric acid cycle?

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

    During catabolism, if roughly 40% of glucose oxidation energy is used to synthesize ATP, what happens to the remaining 60%?

    <p>It is lost as heat. (D)</p> Signup and view all the answers

    What is the primary function of 3-succinyl-CoA synthetase in the citric acid cycle?

    <p>Catalyzes the substrate-level phosphorylation of GDP to GTP (B)</p> Signup and view all the answers

    Which complex in the electron transport chain is directly responsible for accepting electrons from NADH?

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

    What is produced at the end of the electron transport chain when oxygen functions as the electron acceptor?

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

    Which enzyme condenses the acetyl group with oxaloacetate to form citrate?

    <p>Citrate synthase (D)</p> Signup and view all the answers

    What is the ΔG value for the reaction catalyzed by succinate dehydrogenase?

    <p>-56 kcal/mol (B)</p> Signup and view all the answers

    Which of the following compounds is formed from the oxidation of FADH2 in the electron transport chain?

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

    What role does coenzyme Q play in the electron transport chain?

    <p>It accepts electrons from NADH and transfers them further along the chain (B)</p> Signup and view all the answers

    How is oxygen delivered to tissues for use in the electron transport chain?

    <p>It is transported by hemoglobin (B)</p> Signup and view all the answers

    Flashcards

    Succinyl-CoA Synthetase

    Enzyme that catalyzes GDP to GTP in a reaction.

    Succinate Dehydrogenase

    Enzyme on inner mitochondrial membrane acting as complex II in ETC.

    Citrate Synthase

    Enzyme that combines acetyl group with oxaloacetate to form citrate.

    Sources of NADH and FADH2

    Produced by various mitochondrial enzymes during metabolic processes.

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    Oxygen in ETC

    O2 is the final electron acceptor in the electron transport chain.

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    Electron Transport Chain (ETC)

    Series of complexes that transfer electrons derived from NADH and FADH2.

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    NADH Dehydrogenase

    Complex I of the ETC that accepts electrons from NADH.

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    Cytochrome C Oxidase

    Complex IV of the ETC that transfers electrons to oxygen.

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    Citric Acid Cycle

    A key metabolic pathway that oxidizes acetyl-CoA to generate energy carriers.

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    Energy carriers

    Molecules like NADH and FADH2 generated during the citric acid cycle.

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    Guanosine triphosphate (GTP)

    An energy-rich molecule produced in the citric acid cycle alongside NADH and FADH2.

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    Control enzyme: Isocitrate dehydrogenase

    A major control point in the citric acid cycle that is inhibited by NADH and ATP.

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    α-Ketoglutarate dehydrogenase

    An enzyme complex in the cycle that requires several cofactors and is similar to pyruvate dehydrogenase.

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    Role of oxygen

    Oxygen is not directly required for the cycle but is necessary for the electron transport chain.

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    Acetyl-CoA sources

    Includes glucose, fatty acids, ketone bodies, and certain amino acids that fuel the citric acid cycle.

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    Heat loss in energy production

    Approximately 60% of energy from glucose oxidation is lost as heat during metabolism.

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    Uncouplers

    Substances that disrupt the proton gradient in mitochondria, affecting ATP production.

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    2,4-Dinitrophenol (2,4-DNP)

    A well-known uncoupler that increases oxygen consumption and heat generation.

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    Brown adipose tissue

    Fat tissue in newborns that uses uncoupling proteins for heat generation instead of shivering.

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    UCP (Uncoupling Protein)

    Protein in brown fat that allows energy to be dissipated as heat.

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    Toxins as uncouplers

    Bacterial toxins that increase membrane permeability, creating proton leaks.

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    Pneumolysin

    A bacterial toxin produced by Streptococcus pneumoniae, disrupting mitochondrial function.

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    NADH shuttle system

    Transports NADH from cytosol to mitochondria for ATP production.

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    Proton gradient

    Difference in proton concentration across mitochondrial membranes necessary for ATP synthesis.

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    Oxidative Phosphorylation

    Process of ATP synthesis driven by proton gradients using ATP synthase.

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    F1-F0-ATP Synthase

    Enzyme complex that uses proton flow to generate ATP from ADP and Pi.

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    NADH Role in ATP Production

    Oxidation of NADH contributes energy to create about 3 ATP during oxidative phosphorylation.

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    Cyanide Poisoning

    Cyanide binds to cytochrome a/a3, stopping electron transfer to oxygen.

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    Carbon Monoxide Effect

    Carbon monoxide binds to cytochrome a/a3, reducing electron transfer similarly to cyanide.

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    Impact of Inhibitors on ETC

    Inhibitors decrease oxygen consumption and ATP production in the ETC.

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    Proton Channels

    Channels that allow protons to flow back into the mitochondrial matrix, impacting the proton gradient.

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    Study Notes

    Citric Acid Cycle Overview

    • The citric acid cycle, also known as the Krebs cycle or tricarboxylic acid (TCA) cycle, is a key step in cellular metabolism, extracting energy from food molecules.
    • It occurs in the mitochondria.
    • Although oxygen isn't directly required, the cycle cannot proceed anaerobically if NADH and FADH2 accumulate without oxygen.
    • The primary function of the citric acid cycle is oxidizing acetyl-CoA to carbon dioxide.
    • The energy released is captured as NADH, FADH2, and GTP.
    • During catabolism, only about 40% of the energy from oxidizing glucose is used to synthesize ATP; the remaining 60% is lost as heat.

    Citric Acid Cycle Objectives

    • Explain the primary role of the citric acid cycle in cellular metabolism.
    • Understand how the citric acid cycle functions as a key step in extracting energy from food molecules.
    • Gain a comprehensive understanding of the major steps, including participating molecules and enzymes.
    • Explore the reactions within the citric acid cycle, identifying how it regenerates crucial intermediates for further fuel breakdown.
    • Detail how the citric acid cycle generates energy carriers (NADH and FADH2) for ATP production.
    • Explore the connection between the citric acid cycle and the electron transport chain, highlighting their roles in cellular respiration.

    Key Citric Acid Cycle Points

    • Isocitrate dehydrogenase is a major control enzyme, inhibited by NADH and ATP, and activated by ADP.
    • α-ketoglutarate dehydrogenase is similar to the pyruvate dehydrogenase complex, requiring thiamine, lipoic acid, CoA, FAD, and NAD. A lack of thiamine slows acetyl-CoA oxidation in the citric acid cycle.
    • 3-Succinyl-CoA synthetase (succinate thiokinase) catalyzes substrate-level phosphorylation of GDP to GTP.
    • Succinate dehydrogenase is found on the inner mitochondrial membrane and functions as complex II within the electron transport chain.
    • Citrate synthase condenses the incoming acetyl group with oxaloacetate to form citrate.

    Electron Transport Chain (ETC)

    • The ETC is situated in the inner mitochondrial membrane.
    • NADH and FADH2 generated in the citric acid cycle donate electrons to the ETC.
    • Electrons are passed along a series of protein and lipid carriers within the ETC.
    • The ETC culminates in the production of water after the electrons are transferred to oxygen.
    • Importantly, the process produces a proton gradient (a difference in proton concentration across the membrane), crucial for ATP synthesis.

    Oxidative Phosphorylation

    • Oxidative phosphorylation uses the energy stored in the proton gradient to produce ATP from ADP and inorganic phosphate (Pi).
    • ATP synthesis occurs through the F1F0-ATP synthase complex.
    • When NADH is oxidized in the ETC, sufficient energy is provided to phosphorylate approximately 3 ATP molecules.
    • FADH2 oxidation yields approximately 2 ATP molecules.

    ETC Inhibitors

    • Cyanide irreversibly binds to cytochrome a/a3, preventing electron transfer to oxygen.
    • Carbon monoxide binds to cytochrome a/a3, though less tightly than cyanide.
    • Important inhibitors include cyanide, carbon monoxide, etc.

    Uncouplers

    • Uncouplers disrupt the proton gradient, decreasing ATP synthesis and increasing oxygen consumption and NADH oxidation.
    • Examples include 2,4-dinitrophenol (2,4-DNP) and aspirin.
    • Natural uncoupler: Brown adipose tissue (BAT) contains uncoupling protein (UCP), allowing regulated energy loss as heat in newborns.

    Bacterial Toxins as Uncouplers

    • Certain bacterial toxins, such as pneumolysin, staphylococcal α-toxin, and listeriolysin O, can disrupt mitochondrial function by creating membrane pores.
    • This leads to proton leakage and impairs ATP production by uncoupling oxidative phosphorylation.

    Fate of NADH

    • NADH produced in the cytosol during glycolysis needs to be transported into the mitochondria for use in the electron transport chain.
    • Two shuttle systems (glycerol-3-phosphate and malate-aspartate) facilitate the transport of reducing equivalents from cytoplasmic NADH into mitochondria.

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    Description

    Test your knowledge on the Electron Transport Chain (ETC) with this quiz. Explore the roles of different complexes, the mechanisms of ATP synthesis, and the effects of various inhibitors. Understand key concepts related to oxidative phosphorylation and biochemical pathways.

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