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Electron Transport and ATP Synthesis

Electron Transport and ATP Synthesis. C483 Spring 2013. 1. To reduce one molecule of O2, ________ electron(s) must be passed through the electron transport chain and ________ molecule(s) of NADH is(are) oxidized. A) 4; 2 B) 2; 1 C) 1; 1 D) 1; 2 E) 4; 4

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Electron Transport and ATP Synthesis

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  1. Electron Transport and ATP Synthesis C483 Spring 2013

  2. 1. To reduce one molecule of O2, ________ electron(s) must be passed through the electron transport chain and ________ molecule(s) of NADH is(are) oxidized. A) 4; 2 B) 2; 1 C) 1; 1 D) 1; 2 E) 4; 4 2. The chemiosmotic theory is a concept that ________. A) the transport of Na+ and K+ across cell membranes is by active transport B) explains how transport by facilitated diffusion reaches a saturation limit C) explains the blood-brain barrier D) a proton gradient drives the formation of ATP 3. Which is the proper ranking of greatest to least reduction potential? A) NAD+, Q, O2 B) O2, Q, NAD+ C) Q, NAD+, O2 D) Q, O2, NAD+

  3. 4. According to the binding change mechanism, the (alpha3 beta3 ) oligomer of ATP synthase has 3 catalytic sites which can each have ________ different conformations. A) 2 B) 3 C) 6 D) 9 5. The P/O ratio for passing electrons through complexes I, III and IV is ________. A) 1 B) 1.5 C) 2 D) 2.5 E) 3

  4. Goal: ATP Synthesis

  5. Overview • Redox reactions • Electron transport chain • Proton gradient • ATP synthesis • Shuttles Analogy: How does burning coal put flour in the grocery store?

  6. Redox reactions: electricity • 2 e- transfer • Calculate DG by reduction potential • NADH: Eo’ = -.32 • FMN: Eo’=-.30 • DGo’ = -nFDEo’ = -2(96485)(0.02) = -3.9 kJ/mol

  7. Coenzyme Q: Mobile Carrier • FADH2 is a one e- donator • Many reactions, including metals • Ubiquinone is a key intermediate • Can diffuse through nonpolar regions easily

  8. Numerous Redox Substrates • O2: high “reduction potential” • Substrates • Organic cofactors • Metals (iron/sulfur clusters) • cytochromes

  9. Oxygen: the final electron acceptor • Water is produced—has very low reactivity, very stable • Superoxide, peroxide as toxic intermediates • Overall reaction NADH + H+ + ½ O2 NAD+ + H2O

  10. Flow Through Complexes

  11. Downhill Flow of Electrons

  12. Compartmentalization

  13. Protonmotive Force • Flow of electrons is useless if not coupled to a useful process • Battery connected to wire • Proton gradient across mitochondrial membrane

  14. Overview of Complexes I-IV • Don’t need to know which cofactors in which complexes, mechanism of proton pumping • Complex I and II are different entry points into Q pool, which goes to Complex III

  15. Protonmotive Force • NADH + H+ + ½ O2 NAD+ + H2O + 10 H+ pumped • succinate + ½ O2 fumarate + H2O + 6 H+ pumped

  16. Proton Gradient • Gradient driven by concentration difference + charge difference • Free energy of ATP hydrolysis = -48 kJ/mole • How many protons needed to fuel ATP formation? Minimum of 3

  17. Using the Gradient • Coupled to ATP synthesis • Uncouplers used to show link of oxygen uptake and ATP synthesis

  18. Complex V: ATP Synthase • Molecular motor • Rotor: c, g, e • Proton channel

  19. Proton Channel • Protons enters channel between rotor and stator (unit a--purple) • Rotor rotates to release strain by allowing proton to enter matrix • “Stalk” (g) moves inside the “knob”—hexameric ATP synthase • 9 or 10 protons = full rotation

  20. Binding-Change Mechanism • Stalk causes ATP synthase to have three different conformations: open, loose, tight • In “tight” conformation, energy has been used to cause an energy conformation that favors ATP formation • 9 protons = 3 ATP (or 1 ATP/3 protons)

  21. Remember Analogy • Fuelelectricitywater pumped uphillflows down to grind flour • But we don’t have bread until flour is transported to where it needs to go! • Compartmentalization: ATP is in matrix, but must get to the rest of the cell

  22. Active Transport of ATP • ATP must go out, ADP and Pi must go in • Together, use about 1 proton of protonmotive force

  23. Energy Accounting • ATP costs 4 protons • 3 protons in ATP synthase, 1 proton in transport • NADH pumps 10 protons • 4 protons in Complex I, 4 protons in Complex III, and 2 protons in Complex IV • 2.5 ATP/NADH • called P/O ratio--# of phosphorylation per oxygen atom • QH2 pumps 6 protons • 4 protons in Complex III and 2 protons in Complex IV • 1.5 ATP/QH2

  24. Net ATP Harvest from Glucose • Glycolysis = 2 ATP • Plus 3 or 5 ATP from NADH • What leads to difference in this case? • Pyruvate DH = 5 ATP • Citric Acid Cycle = 20 ATP • Total: 30-32 ATP/glucose

  25. NADH Shuttles • Glycerol phosphate shuttle (1.5 ATP/NADH) • Produces QH2 • Operational in some tissues/circumstances

  26. NADH Shuttles • Malate-Aspartate shuttle (2.5 ATP/NADH) • Actually slightly less because one proton is consumed in shuttle • Separate NAD+/NADH pools indirectly interconverted • Operational in some tissues/circumstances

  27. Answers • A • D • B • B • D

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