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Bioenergetics, the TCA Cycle & Oxidative Phosphorylation

Tier 1 · #7 of 33 · highest yield · topic 3.1 — every high-yield fact from the book chapter, exam-ready.

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  1. Front
    How many ATP are produced per NADH oxidized in the respiratory chain (modern P/O ratio)?
    Back
    2.5 ATP
  2. Front
    What three irreversible reactions of the TCA cycle serve as its regulatory points?
    Back
    Citrate synthase (step 1), isocitrate dehydrogenase (step 3), and α-ketoglutarate dehydrogenase (step 4)
  3. Front
    How many ATP are produced per FADH₂ oxidized in the respiratory chain (modern P/O ratio)?
    Back
    1.5 ATP
  4. Front
    Which respiratory chain complex does NOT pump protons?
    Back
    Complex II ( succinate dehydrogenase )
  5. Front
    How many ATP are generated per acetyl-CoA from one complete turn of the TCA cycle?
    Back
    10 ATP (3 NADH × 2.5 + 1 FADH₂ × 1.5 + 1 GTP )
  6. Front
    In what subcellular compartment does the TCA cycle take place?
    Back
    The mitochondrial matrix
  7. Front
    Which TCA cycle enzyme is also Complex II of the respiratory chain?
    Back
    Succinate dehydrogenase
  8. Front
    Which respiratory chain inhibitors block Complex IV by binding cytochrome a₃ iron?
    Back
    Cyanide (CN⁻) , carbon monoxide (CO) , sodium azide (NaN₃) , and hydrogen sulfide (H₂S)
  9. Front
    Which TCA cycle enzyme catalyzes the only substrate-level phosphorylation in the cycle?
    Back
    Succinyl-CoA synthetase
  10. Front
    What high-energy molecule is the direct product of substrate-level phosphorylation in the TCA cycle?
    Back
    GTP
  11. Front
    Which complex is the entry point for electrons from NADH into the respiratory chain?
    Back
    Complex I ( NADH-CoQ oxidoreductase / NADH dehydrogenase )
  12. Front
    How does the action of an uncoupler (e.g., 2,4-DNP ) affect electron flow / O₂ consumption?
    Back
    Electron flow and O₂ consumption accelerate (the gradient no longer impedes pumping)
  13. Front
    Cloze: The first step of the TCA cycle, citrate synthase condensing ____ with the acetyl group, forms citrate .
    Back
    oxaloacetate (OAA)
  14. Front
    At which respiratory chain complex do Rotenone and amobarbital (amytal) block electron flow?
    Back
    Complex I (at the FMN -to- Fe-S step)
  15. Front
    What is the most important anaplerotic enzyme, and what reaction does it catalyze?
    Back
    Pyruvate carboxylase : pyruvate + CO₂ + ATP → oxaloacetate
  16. Front
    What molecule allosterically activates pyruvate carboxylase ?
    Back
    Acetyl-CoA
  17. Front
    Approximately how much energy does hydrolysis of an ATP phosphoanhydride bond release under standard conditions?
    Back
    ~30.5 kJ/mol
  18. Front
    Where does Antimycin A block the respiratory chain?
    Back
    Complex III (between cytochrome b and cytochrome c₁ )
  19. Front
    Which two TCA cycle reactions release CO₂?
    Back
    Isocitrate dehydrogenase (step 3) and α-ketoglutarate dehydrogenase (step 4)
  20. Front
    What is the competitive inhibitor of succinate dehydrogenase , and why does it inhibit?
    Back
    Malonate — it is a structural analog of succinate
  21. Front
    Cloze: The main electron carrier of catabolism is NAD⁺ (reduced to NADH ), while ____ provides reducing power for anabolic/biosynthetic reactions.
    Back
    NADPH
  22. Front
    What does oligomycin block, and what is the dual consequence?
    Back
    It blocks the F₀ proton channel of ATP synthase ; both ATP synthesis AND electron flow stop (the gradient cannot be dissipated)
  23. Front
    What is the rate-limiting step of ATP synthase ?
    Back
    Release of ATP from the T (tight) state — not the chemical synthesis of ATP
  24. Front
    Which TCA cycle enzyme regenerates oxaloacetate , and what carrier does it reduce?
    Back
    Malate dehydrogenase ; it reduces NAD⁺ to NADH
  25. Front
    What is the physiological uncoupler in brown adipose tissue , and what does it do?
    Back
    Thermogenin (UCP-1) — it lets protons re-enter the matrix without making ATP, generating heat
  26. Front
    In which population is brown adipose tissue found predominantly?
    Back
    Newborns (in the neck and upper back )
  27. Front
    Why do anaerobic conditions inhibit the TCA cycle?
    Back
    NADH accumulates and NAD⁺ is depleted (no chain to reoxidize it), so the dehydrogenase reactions stall
  28. Front
    Cloze: ____ is the classic artificial uncoupler — a lipid-soluble weak acid that shuttles protons across the inner mitochondrial membrane .
    Back
    2,4-dinitrophenol (2,4-DNP)
  29. Front
    What is the terminal enzyme of the respiratory chain and the only step that consumes O₂?
    Back
    Complex IV ( cytochrome c oxidase )
  30. Front
    Which TCA enzyme isomerizes citrate to isocitrate ?
    Back
    Aconitase
  31. Front
    Why does FADH₂ yield fewer ATP than NADH ?
    Back
    It enters at Complex II , which does not pump protons , so it bypasses Complex I 's proton pumping
  32. Front
    What mobile, lipid-soluble carrier shuttles electrons from Complexes I and II to Complex III ?
    Back
    Coenzyme Q ( ubiquinone, CoQ )
  33. Front
    What three mechanisms can the cell use to make ATP?
    Back
    Photosynthetic phosphorylation , substrate-level phosphorylation , and oxidative phosphorylation
  34. Front
    Name the three high-energy substrates of substrate-level phosphorylation listed in the chapter.
    Back
    Phosphoenolpyruvate (PEP) , 1,3-bisphosphoglycerate (1,3-BPG) , and succinyl-CoA
  35. Front
    How many protons are pumped out of the matrix when 2 electrons pass from NADH to O₂?
    Back
    10 H⁺
  36. Front
    How many protons are pumped when 2 electrons pass from FADH₂ to O₂?
    Back
    6 H⁺ ( Complex I is bypassed)
  37. Front
    Cloze: Citrate synthase is irreversible because oxaloacetate is kept at very low concentration (below 10⁻⁶ M), which provides a thermodynamic ____ driving the reaction forward.
    Back
    pull
  38. Front
    Whose theory explains that electron transport and ATP synthesis are coupled through a physical proton gradient rather than a chemical intermediate?
    Back
    Mitchell's chemiosmotic theory
  39. Front
    What term describes the TCA cycle's dual role as both catabolic and anabolic?
    Back
    Amphibolic
  40. Front
    Which prosthetic group and centers does Complex I contain for electron transfer?
    Back
    FMN and multiple iron-sulfur (Fe-S) centers
  41. Front
    Cloze: Unlike freely diffusible NAD⁺ , FAD is ____ to its enzyme (a flavoprotein).
    Back
    tightly bound
  42. Front
    What dietary vitamin is the precursor for both FAD and FMN ?
    Back
    Riboflavin (vitamin B₂)
  43. Front
    How many H⁺ must flow back through ATP synthase (including the Pi symport) to synthesize one ATP?
    Back
    4 H⁺ (3 through the F₀ rotor + 1 as Pi symport)
  44. Front
    Which mobile carrier passes electrons from Complex III to Complex IV ?
    Back
    Cytochrome c
  45. Front
    In a patient poisoned by a Complex IV inhibitor , which respiratory component will be MOST fully reduced?
    Back
    Cytochrome c (the direct electron donor to Complex IV )
  46. Front
    Which two-carbon compound must every fuel be converted to before complete oxidation in the TCA cycle?
    Back
    Acetyl-CoA
  47. Front
    What mechanistic trick does Complex III use to reconcile a two-electron donor ( CoQH₂ ) with a one-electron acceptor ( cytochrome c )?
    Back
    The Q cycle
  48. Front
    Cloze: Brown adipose tissue's UCP-1 is activated by hormone-induced fatty acid release , whereas the related proteins ____ and UCP-3 are activated by thyroid hormones .
    Back
    UCP-2
  49. Front
    What is the only irreversible step of the respiratory chain?
    Back
    Complex IV ( cytochrome c oxidase reducing O₂ to water)
  50. Front
    Approximately what percentage of total ATP production does the TCA cycle account for (via feeding electrons to oxidative phosphorylation)?
    Back
    66%
  51. Front
    What is the standard reduction potential of the NAD⁺/NADH couple?
    Back
    −0.320 V
  52. Front
    What enzymes interconvert ATP with the energetically equivalent UTP, GTP, and CTP ?
    Back
    Nucleoside diphosphokinase and nucleoside monophosphokinase
  53. Front
    Which TCA enzyme hydrates fumarate to malate ?
    Back
    Fumarase
  54. Front
    Which channels make the outer mitochondrial membrane freely permeable to molecules up to ~10 kDa?
    Back
    Porin channels
  55. Front
    Key contrast: how do a chain inhibitor (e.g., cyanide ) and an uncoupler (e.g., DNP ) differ in their effect on O₂ consumption?
    Back
    Chain inhibitor stops O₂ consumption ; uncoupler accelerates O₂ consumption (both stop ATP synthesis)
  56. Front
    Which two amino acids feed the TCA cycle as α-ketoglutarate via anaplerosis ?
    Back
    Glutamate and glutamine
  57. Front
    Which two ratios feedback-inhibit isocitrate dehydrogenase and the α-ketoglutarate dehydrogenase complex when the cell is energy-replete?
    Back
    A high [NADH]/[NAD⁺] ratio and a high [ATP]/[ADP] ratio
  58. Front
    Which two TCA cycle enzymes are the direct sites of feedback inhibition by high NADH and ATP (respiratory control)?
    Back
    Isocitrate dehydrogenase and the α-ketoglutarate dehydrogenase complex
  59. Front
    What term describes the slowing of the TCA cycle and respiratory chain when ATP and NADH are abundant?
    Back
    Respiratory control
  60. Front
    What are the two physical components of the proton-motive force across the inner mitochondrial membrane ?
    Back
    A pH gradient (matrix ~1 pH unit more alkaline) and an electrical potential (matrix negatively charged)
  61. Front
    In what direction does the matrix pH shift as protons are pumped out, and by how much?
    Back
    The matrix becomes more alkaline by about 1 pH unit
  62. Front
    What is the approximate electrical potential of the matrix relative to the intermembrane space ?
    Back
    About −0.15 V (matrix is negatively charged)
  63. Front
    In ATP synthase , what does the F₀ domain consist of and where is it located?
    Back
    A ring of 12 c-subunits embedded in the inner mitochondrial membrane (it rotates as protons flow through)
  64. Front
    In ATP synthase , what is the subunit composition of the F₁ domain?
    Back
    Three α and three β subunits arranged around a central γ subunit (stalk), protruding into the matrix
  65. Front
    Name the three conformational states the β subunits of ATP synthase cycle through, and what each does.
    Back
    O (open) — releases ATP / low affinity; L (loose) — binds ADP + Pi ; T (tight) — synthesizes ATP
  66. Front
    Which ATP synthase β-subunit conformation binds ADP + Pi ?
    Back
    L (loose)
  67. Front
    Cloze: In ATP synthase the β-subunit state that tightly binds ligands and catalyzes ATP synthesis is the ____ state.
    Back
    T (tight)
  68. Front
    For fatty-acid synthesis, which TCA intermediate exits the mitochondria to supply acetyl groups in the cytosol ?
    Back
    Citrate
  69. Front
    Which TCA cycle intermediate is withdrawn for heme synthesis?
    Back
    Succinyl-CoA
  70. Front
    Which two TCA intermediates are drawn off as precursors for amino-acid synthesis?
    Back
    α-ketoglutarate and oxaloacetate (OAA)
  71. Front
    Which two amino acids enter the TCA cycle as oxaloacetate via anaplerosis ?
    Back
    Aspartate and asparagine
  72. Front
    ATP hydrolyzes spontaneously in water, yet it can be stockpiled and released on demand. Why?
    Back
    It is kinetically stable — the hydrolysis rate is slow without an enzyme
  73. Front
    Approximately what percentage of the body's oxygen does the respiratory chain consume?
    Back
    About 90%
  74. Front
    Why can Complex IV run at near-maximal rate even when O₂ concentration is very low?
    Back
    It has an exceptionally high affinity for oxygen
  75. Front
    Which metal centers does Complex IV ( cytochrome c oxidase ) contain?
    Back
    Copper centers (CuA, CuB) and heme groups cytochrome a and cytochrome a₃
  76. Front
    What is the standard reduction potential of the ½O₂/H₂O couple?
    Back
    +0.816 V
  77. Front
    What equation relates the free energy released by electron transfer to the difference in reduction potential?
    Back
    ΔG = −nFΔE
  78. Front
    What is the approximate total free energy released when electrons pass from NADH to O₂?
    Back
    About −218 kJ/mol
  79. Front
    How many high-energy phosphoanhydride (anhydride) bonds does ATP contain?
    Back
    Two (linking the three phosphates)
  80. Front
    Why is the impermeability of the inner mitochondrial membrane essential to oxidative phosphorylation?
    Back
    It lets the proton gradient build up and be maintained (protons can't leak back across)
  81. Front
    Cloze: The pyruvate dehydrogenase complex and the α-ketoglutarate dehydrogenase complex share the same architecture — several enzymes held physically together so intermediates are directly ____.
    Back
    channeled (substrate channeling, improving efficiency)
  82. Front
    Which respiratory chain component is the major site of reactive oxygen species (ROS) generation under pathological conditions?
    Back
    Coenzyme Q (its semiquinone radical, CoQH• , is a stable intermediate)
  83. Front
    What was 2,4-dinitrophenol historically used for, and why was it banned?
    Back
    Used as a weight-loss drug in the 1930s; banned because it caused deaths from hyperthermia (it is highly toxic)
  84. Front
    Which nucleoside triphosphate is the direct energy donor that drives glycogen synthesis?
    Back
    UTP

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