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Oxidative Phosphorylation

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How does the mitochondria generate energy using the electron transport chain?
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Oxidative Phosphorylation

  1. 1. Bioenergetics The concepts, the ETC, and importance
  2. 2. Activation energy Negative G means that the unstable compound A readily undergoes the reaction to reach a more energetically stable compound B
  3. 3. Positive G means that the stable compound B will not readily enter the reaction and must be provided this energy to become compound A
  4. 4. Coupling • An energetically unfavorable reaction is linked to one that is favored • Exothermic reactions release heat which can be used by endothermic reactions that absorb heat to move the reaction forward by overcoming the high Activation Energy (Ea) • Usually occurs when there is a common intermediate, as in reactions that occur sequentially
  5. 5. The Electron Transport Chain • This chain uses the concept of free energy to move the high energy e- towards a lower state. At each step, e- loses energy in ‘packets’ • This is an overall oxidative process because oxygen is the final electron acceptor
  6. 6. Importance • ETC does not directly generate ATP. • The ETC actually uses the energy released to create an acidic environment within the intermembranous space of the mitochondria 2 e- (NADH) : 10 H+ pumped
  7. 7. Complex I Complex II CoQ Complex III Cyto C Complex IV 4 H+ 0 0 (Links) 4 H+ 0 2 H+ Cyto C is actually present in the IMS
  8. 8. How does each complex transfer electrons? • NAD+  H- [hydride ions] • FMN, FAD, and CoQ  H atoms • Cytochromes  electrons
  9. 9. Energetics NADH and FMN form a redox pair with NADH donating H to be oxidized and FMN accepting H to be reduced This is because NADH is a much stronger reducing agent and will easily give up its H, as evidenced by its larger E0. This also means that NADH will consequently generate will more energy as well
  10. 10. ATP • Each high energy phsophate requires 7.3 kCal mol-1 energy to cleave. • ATP is valuable as an energy currency as this energy can be used to overcome the energy barrier • This means that ADP/AMP must receive the same amount of energy to reform the bond
  11. 11. • A larger E0 means that the free energy produced will be higher • To convert ADP to ATP, 7.3 kCal mol-1 energy is needed • NADH produces 52.6 kCal energy • P/O ratio (ATP made per reduced O atom) is therefore NADH:ATP = 1:3 • FADH releases less energy. FADH:ATP = 1:2
  12. 12. Coupling • Through this concept, ATP is generated • It is the coupling of the actions of the ETC to the enzyme ATP Synthase • The established electrical gradient is the coupler
  13. 13. ATP Synthase Movement down the electrochemical gradient
  14. 14. Blocking the Pathway
  15. 15. • All the reactions are tightly coupled to each other • Blocking the ETC causes ATP synthesis to stop Amytal, Rotenone  CoQ Antimycin A  Cyto c CN-, CO, H2S, NaN3  O2 ETC
  16. 16. ATP Synthase • Its action can be blocked by the drug oligomycin which binds to the F0 component • The ions cannot move down their gradient • No ATP production • It highlights the importance of the tight coupling caused by the electrical gradient. This checkpoint is known as the respiratory control
  17. 17. Uncoupling • The IMM is made permeable to H+ ions which results in the dissipation of the electrochemical gradient • H+ moves down the gradient. While there is heat release, no ATP is produced • Proteins or drugs that do this are called uncouplers
  18. 18. UCP or Thermogenin • Natural, present in all mammals • Especially important in infants that have large amounts of brown fat • Heat is used by body. This is non-shivering thermogenesis • Cold increases UCP expression through catecholamines
  19. 19. Synthetic Uncouplers • These are lipophilic compounds that carry the H+ by binding with it (ionophores) • 2,4-dinitrophenol • Aspirin and salicylates are uncouplers in high doses for this reason. Their toxicity is accompanied with a fever
  20. 20. Transport • ADP and ATP enter or leave by antiporters or symporters • NADH enters through glycerol-3-phosphate or by the malate shuttle

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