Electron Transport Chain/Respiratory Chain

1. Electron Transport Chain/Respiratory Chain Proton gradient formed Four large protein complexes Mitochondria localized Energetically favorable electron flow

2. Mitochondrion Inner Membrane Respiration site Surface area for humans ca. 3 football fields Highly impermeable (no mitochondrial porins) Matrix and cytoplasmic sides

3. Standard Reduction Potentials

4. Favorable Electron Flow: NADH to O2 Net electron flow through electron transport chain: ½O2 + 2H+ + 2e- H2O ΔE˚΄ = + 0.82V NAD+ + H+ + 2e- NADH ΔE˚΄ = - 0.32V Subtracting reaction B from A: ½O2 + NADH + H+ H2O + NAD+ΔE˚΄ = + 1.14V ΔG˚΄ = -220 kJ mol-1 ΔG˚΄ = -nF Δ E˚΄F = 96,480 J mol-1 V-1

5. Electron Transport Energetic’s

6. Electron Transport Chain Components Protein complexes: NADH-Q reductase Succinatedehydrogenase Cytochrome C reductase Cytochrome C oxidase Bridging components: Coenzyme Q and Cytochrome C What is the driving force for this electron flow?

7. Coupled Electron-Proton Transfer Through NADH-Q Oxidoreductase FMN bridges: NADH 2 e- donor with FeS 1 e- acceptor L-shaped Complex I Overall reaction: NADH + Q + 5H+ NAD+ + QH2 + 4H+

8. Coupled Electron-Proton Transfer Through NADH-Q Oxidoreductase H+ movement with 1 NADH Iron-sulfur clusters (a.k.a. nonheme-iron proteins) 2Fe – 2S or 4Fe – 4S complexes

9. NADH-Q Oxidoreductase (Complex I) Structure Largest of respiratory complexes Mammalian system contains 45 polypeptide subunits; 8 Fe-S complexes; 60 transmembrane helices

10. Different Quinone (Q) Oxidation States QH2 generated by complex I & II Membrane-bound bridging molecule Overall reaction: QH2 + 2Cyt Cox + 2H+ Q + 2Cyt Cred + 4H+ X

11. Oxaloacetate Enzyme Regeneration from Succinate • SuccinateDehydrogenase • Fumerase • MalateDehydrogenase

12. Pathways that Contribute to the Ubiquinol Pool Without Utilizing Complex I

13. Alternative Q-Cycle Entry Points Complex I Complex II (citric acid cycle) Glycerol 3-phosphate shuttle Fatty acid oxidation (electron-transferring-flavoproteindehydrogenase)

14. Electron-Transport Chain Reactions in the Mitochondria

15. The Q Cycle Electron transfer to Cytochrome c Reductase via 3 hemes and a Rieske iron-sulfur center Overall reaction: QH2 + 2Cyt Cox + 2H+ Q + 2Cyt Cred + 4H+ ISP – iron sulfur protein

16. The Q Cycle

17. Cytochrome c Oxidoreductase Structure • Heme-containing homodimer with 11 subunit monomers • Functions to: • Transfer e- to Cyt c • Pump protons into the intermembrane space Intermembrane side Matrix side

18. Cytochrome c Oxidase: Proton Pumping and O2 Reduction

19. Cytochrome c Oxidase: O2 Reduction to H2O Reaction shown: 2Cyt Cred + 2H+ + ½ O2 2Cyt Cox + H2O Overall reaction: 2Cyt Cred + 4H+ + ½ O2 2Cyt Cox + H2O + 2H+

20. Cytochrome c Oxidase Intermembrane space Oxygen requiring step 13 subunits; 10 encoded by nuclear DNA CuA/CuA prosthetic group positioned near intermembrane space O2 to H2O reduction site Matrix

21. Cytochrome c Oxidase

22. Electron-Transport Chain Reactions in the Mitochondria

23. Electron-Transport Chain Reactions in the Mitochondria

24. Mitochondrial Electron-Transport Chain Components

25. ATP Synthesis via a Proton Gradient The two major 20th century biological discoveries: DNA structure and ATP synthesis

26. ATP-Driven Rotation in ATP-Synthase: Direct Observation γ rotation with ATP present With low ATP 120-degree Incremental rotation Glass microscope slide

27. ATP Synthase with a Proton-Conducting (F0) and Catalytic (F1) Unit Intermembrane side F1 matrix unit contains 5 polypeptide chain types (α3, β3, γ, δ, ε) Proton flow from intermembrane space to matrix Matrix side

28. ATP-Synthase with Non-Equivalent Nucleotide Binding Sites F1 contains: α3, β3heximeric ring and γ, ε central stalk Central stalk and C-ring form the rotor and remaining molecule is the stator Top view Side view Matrix side

29. γ-Rotation Induces a Conformational Shift in the β Subunits Each β subunit interacts differently with the γ subunit ATP hydrolysis can rotate the γ subunit

30. Proton Flow Around C-Ring Powers ATP Synthesis Subunit C Asp protonation favors movement out of hydrophylic Subunit a to membrane region Deprotonation favors Subunit a movement back in contact with Subunit a

31. Proton Motion Across the Membrane Drives C-Ring Rotation

32. C-Ring Tightly Linked to γ and ε Subunits C-ring rotation causes the γ and ε subunits to turn inside the α3β3hexamer unit of F1 Columnar subunits (2 b) with δ prevent rotation of the α3β3hexamer unit What is the proton to ATP generation ratio?

33. Mitochondrial ATP-ADP Translocase Net movement down the concentration gradient for ATP (out of matrix) and ADP (into matrix) No energy cost

34. Mitochondrial Transporters for ATP Synthesis Net movement against the concentration gradient for Pi (into matrix) and charge balance -OH (out of matrix) Proton gradient energy cost

35. ATP Yield With Complete Glucose Oxidation

36. Heat Generation by an Uncoupling Protein UCP-1 Brown adipose tissue rich in mitochondria for heat generation Pigs nest, shiver, and have large litters to compensate for lack of brown fat

37. ATP Synthesis Chemical Uncoupling What physiological effect might DNP have in humans?

38. Electron Transport Chain Inhibitors Toxins (e.g. fish and rodent poison rotenone) Site specific inhibition for biochemical studies What impact will rotenone have on respiration (O2 consumption)?

39. Proton Gradient Central to Biological Power Transmission

40. Problems: 13, 21, 23, 31, 33