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How is the energy of Oxidation Preserved for the synthesis of ATP?

How is the energy of Oxidation Preserved for the synthesis of ATP?. ANS: Electron transfer to oxygen is accompanied by the formation of a high energy proton gradient. The Gradient arises by having protons pumped from the matrix side of the mitochondria to

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How is the energy of Oxidation Preserved for the synthesis of ATP?

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  1. How is the energy of Oxidation Preserved for the synthesis of ATP? ANS: Electron transfer to oxygen is accompanied by the formation of a high energy proton gradient. The Gradient arises by having protons pumped from the matrix side of the mitochondria to the inner membrane spaces Back flow of the protons to the matrix leads to the synthesis of ATP.

  2. H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ O2 O2 O2 O2 O2 O2 O2 Cyt C H2O H2O H2O H2O H2O H2O H2O H+ Inner membrane space H+ H+ H+ H+ H+ H+ I III IV NADH II H+ H+ H+ H+ H+ Matrix side PROTON GRADIENT FORMATION (The Chemiosmotic Model of Energy Conservation

  3. The Q-Cycle (Complex III-Cytbc1 complex) One electron goes on to Cytoc1, the other stays in the Q cycle Text p700

  4. 2 protons come from QH2 2 protons come from matrix QH2 + 2 cytc1 (oxidized) + 2H+N (matrix side) Q + 2 cytc1 (reduced) + 4H+P (inner membrane)

  5. 4. Given A. The chemical potential of A is said to be GA or the partial molar free energy of A. GA - Go’A = RTln[A] Free Energy Considerations (Chapt 11, p 398) 1. All substances in solution have a chemical potential 2. The chemical potential is related to concentration 3. Chemical potential is related to free energy 5. In terms of free energy of A: This equation says the free energy of A depends on the concentration of A

  6. Equation assumes A goes from out to in GA = GA(in) - GA (out) [A]out [A]in = RT ln = RT ln [A]in [A]out [A]in - RT ln = [A]out A across a membrane 1. A difference in the concentration of A across a membrane creates a chemical potential difference 2. The difference is the difference of the chemical potential on either side: 3. A in to out:

  7. [A]in [A]out [A]in DGA = RT ln DGA = RT ln [A]in [A]out [A]out Proton Gradient Energy How much energy must be expended to transfer a proton from the matrix to the inner membrane? A outside A A A A A A A A A A A A inside A A A A A A A = RT ln Since [A]in < [A]out Since [A]in < [A]out DGA = negative DGA = positive Spontaneous Endergonic Requires ATP

  8. Electrochemical potential DGH+ = 2.3RT DpH + ZFDY [H+]out [A]in DGA = RT ln [A]out [H+]in DGH+ = RT ln + ZFDY DGH+ = 2.3RT log [H+]out - log[H+]in + ZFDY DGH+ = 2.3RT [pH (in) – pH (out)] + ZFDY Proton Gradient Energy The CHEMIOSMOTICPrinciple If A is ionic (has a charge) A+ Read Chapter 19 p703 outside + + + + + + Dy inside – – – – – Z = charge on ion H+ F = Faraday’s constant + ZFDY

  9. = 5.70 kJ/mol x DpH + (1) 96.5 kJ/mol-volt x DY volts DGA = 2.3RT DpH + ZFDY Problem: Calculate the pmf of a mitochondrial membrane that has a membrane potential of 168 mV and whose matrix pH is 0.75 units higher than its intramembrane space. = 5.70 x (.75) + 96.5 x .168 = 4.12 kJ/mol + 16.21 kJ/mol pH gradient (20%) Membrane potential (80%) = 20.45 kJ/mol of protons The pH gradient and the Membrane potential both contribute to the proton motive force.

  10. ADP + Pi ATP + H2O F1 = stalk and lollypop Fo = base How is ATP made? DG = + 30.5 kJ/mol FoF1 ATPase Complex (ATP Synthase) 1. An ATP making machine 2. Driven by a proton gradient 3. Attached to the inner mitochondria membrane

  11. 3 non-equivalent sites H+ Matrix F1 FO Intermembrane space FOF1 ATPase (ATP Synthase) Binding-Change Model

  12. Loose Site Tight Site ATP ab (ADP and Pi bind) ADP + Pi F1 Open Site (ATP is released) (ATP is formed and held) ATP ab ab 3-Site Model of ATP Synthesis The flow of protons through F1 makes the sites alternate much like a spinning propeller.

  13. Site 1 Site 2 Site 3 ADP + Pi ATP ADP + Pi ATP ADP + Pi ATP Older Model of ATP Synthesis FADH2 NADH FMN CoQ Cyt b Cyt c1 Cyt c Cyt a+a3 O2 Model was tested by measuring P/O ratios

  14. NADH ~3 ~2 FADH2 ~2 Succinate P/O Ratios What is it? P is phosphate taken up (incorporated into ATP) O is the oxygen taken up (measured as atomic oxygen) (Equated to a pair of electrons traveling to O2) What is the significance? Compares substrate efficacy to form ATP Examples: P/O Assumed to be whole intergers based on the “coupling site” model of ATP synthesis

  15. Chemiosmotic Adjustment to P/O • 10 protons are pumped for each electron pair from NADH • 6 protons are pumped for each electron pair from FADH2 • 4 protons are required to make one ATP • 1 of the 4 is used in transport of ADP, Pi and ATP across mitochondrial membrane • Therefore, 10/4 or 2.5 is the P/O ratio for NADH • Therefore, 6/4 or 1.5 is the P/O ratio for FADH2

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