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Glucose metabolism

Glucose metabolism. Glycolysis: 2 NADH, 2 ATP (net) Pre-TCA cycle: 2 NADH TCA cycle: 6 NADH, 2 FADH 2 , 2 A/GTP. Some ATP Big bonus: NADH, FADH 2 → REDUCING POWER. Energy harvest by respiration. Carbon-carbon bonds: chemical energy NADH, FADH 2 : energy of oxidation

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Glucose metabolism

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  1. Glucose metabolism • Glycolysis: 2 NADH, 2 ATP (net) • Pre-TCA cycle: 2 NADH • TCA cycle: 6 NADH, 2 FADH2, 2 A/GTP Some ATP Big bonus: NADH, FADH2→ REDUCING POWER

  2. Energy harvest by respiration • Carbon-carbon bonds: chemical energy • NADH, FADH2: energy of oxidation • Proton gradient: potential energy • ATP synthesis: useable chemical energy

  3. Reducing power/Energy of oxidation • Not very user-friendly • How to harvest the energy? • Electron transport chain • Change energy of oxidation into potential energy (H+ gradient) • Change potential energy into chemical energy (F1Fo ATP synthase)

  4. What is energy of oxidation? • Reducing potentials: NAD+ + H+ + 2e-→ NADH E'° ~ -0.414V ubiquinone + 2H+ + 2e- → ubiquinol E'° ~ +0.045 Electrons (e-) flow spontaneously from NADH to ubiquinone NADH IS A STRONGER REDUCING AGENT THAN UBIQUINOL ubiquinone NADH (oxidized form) (reduced form)

  5. Cataloging the red/ox reactionTransfer of e- from NADH to ubiquinone E'° (V) NADH → NAD+ + H+ + 2e- +0.414 ubiquinone + 2H+ + 2e-→ ubiquinol +0.045 NADH + ubiquinone + H+→ ubiquinol + NAD+ +0.459 *extra energy* not yet useable DE'° > 0 ~ DG'° < 0

  6. Electrons are passed among redox carriers REDUCINGSTRENGTH NADH→NAD+ FMN (↔FMNH2) Fe-S Cluster Ubiquinone (coenzyme Q) Cytochrome C Couple energetically favorable reactions to energetically unfavorable reactions Overall -DG O2→H2O

  7. Redox energy is transformed into potential energy MATRIX Generation of NADH INTERMEMBRANESPACE

  8. Flow of H+into the matrix Is energetically favorable 1. Input energy to move H+ out 2. Harvest energy INTERMEMBRANESPACE Low pH (higher [H+]) Electrically positive MATRIX High pH (lower [H+]) Electrically negative

  9. Mitochondria actually look like the cartoons http://www.tmd.ac.jp/ http://faculty.ircc.edu

  10. Redox energy is transformed into potential energy Establishment of a chemical and electric gradient across the inner membrane F1Fo ATP synthase Transforms potential Energy into useable Chemical energy

  11. Electron transport between electron carriers occurs in protein complexes within the inner membrane

  12. Complex I • NADH: Ubiquinone oxidoreductase • 850kDa, 43 subunits • Converts NADH to NAD+ • e- transferred through complex • FMN, Fe-S clusters • 4 protons are ‘pumped’ from the matrix into the intermembrane space • Reduces ubiquinone (Q) to ubiquinol (QH2)

  13. Ubiquinol (reduced coenzyme Q)

  14. Complex III • Coenzyme Q:cytochrome c oxidoreductase • 250 kDa • 11 subunits • 2 coQ oxidized, one CytC reduced • e- carriers: • Hemes, Fe-S clusters • Net 4 H+ pumped to intermembrane space

  15. Complex III, cont.

  16. Cytochrome C • Heme group carries electrons • Loosely associated with membrane • Shuttles e- from complex III to IV

  17. Complex IV • Cytochrome C oxidase • 160 kDa • 13 subunits • Reduces oxygen • ½ O2 + 2H+ + 2e-→ H2O

  18. Complex II (Use of FADH2) • Succinate dehydrogenase • Membrane-bound enzyme in the TCA cycle • 140 kDa • 4 subunits • FAD, Fe-S clusters carry electrons • e- transferred ubiquinone(Q) • QH2 carries e- to complex 3

  19. Electron transport

  20. Overall reaction starting with 2 e- from one NADH NADH + H+ + ½ O2→ NAD+ + H2O DG'° ~ -220 kJ/mol (of NADH) -highly favorable -coupled to transport of ~10 H+ against a chemical/electrical gradient

  21. Oxidative phosphorylation • Involves reduction of O2 to H2O by NADH and FADH2 • ATP synthesized through e- transfers • Inner mitochondrial membrane • Embedded protein complexes • Succinate dehydrogenase • Impermeable to most small molecules (and H+) • Creation of electrochemical gradients

  22. ATP generation • 2 NADH, 2 ATP from glycolysis (glucose) • 1 NADH from pre-TCA (each pyruvate) • 3 NADH, FADH2 from TCA (each acetyl CoA) • 2 e- from NADH yields 2.5 ATP* • 2 e- from FADH2  yields 1.5 ATP

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