Electron Transport Chain

1. Electron Transport Chain

2. Electron Transport Chain

3. Mitochondrial Structure

4. Electron Transport Chain Overview The ETC removes energy stored in the NADH and FADH2 molecules to: • create a proton gradient across the inner mitochondrial membrane • convert O2 to H2O. All reactions are redox reactions.

5. Electron Transport Chain Animation ETC Animation

6. ETC Components

7. ETC Components: Complex I • Complex 1: NADH Dehydrogenase • 2 e- from NADH are transferred to Complex I • Protons are pumped across the inner mitochondrial membrane (IMM) by Complex I (active Transport)

8. ETC Components: Q • e- are transferred from Complex I to ubiquinone (Q) • Q is a mobile component within the IMM

9. ETC Components: Complex III • Complex III: Cytochrome b-c1 • e- are transferred from Q to Complex III • Protons are pumped across the IMM by Complex III

10. ETC Components: Cyt C • e- are transferred from Complex III to cytochrome c (cyt c) • cyt c is a mobile component on the surface of IMM, in the intermembrane space

11. ETC Components: Complex IV • Complex IV: CytochromeOxidase • e- are transferred from cyt c to Complex IV • Protons are pumped across the IMM by Complex IV

12. ETC Components: O2 • O2 is the final electron acceptor of the ETC • enough e- pass through the ETC to produce full H2O molecules

13. Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP H+ H+ H+ Cyt c Protein complex of electron carners Intermembrane space Q IV I III Inner mitochondrial membrane II H2O FADH2 2 H+ + 1/2 O2 FAD+ NADH+ NAD+ (Carrying electrons from, food) Mitochondrial matrix Electron transport chain Electron transport and pumping of protons (H+), which create an H+ gradient across the membrane Figure 9.15 FADH2 Pathway FADH2 FAD

14. FADH2 Pathway • 2e- are transferred from FADH2 to Complex II • no protons are pumped across the IMM • e- are transferred from Complex II to Q and proceed through the rest of ETC

15. NADH 50 FADH2 Multiproteincomplexes I 40 FAD FMN II Fe•S Fe•S O III Cyt b 30 Fe•S Cyt c1 IV Free energy (G) relative to O2 (kcl/mol) Cyt c Cyt a Cyt a3 20 10 0 O2 2 H + + 12 H2O ETC Thermodynamics • FADH2 enters the chain at a lower energy than NADH • 2 electrons from NADH produce a max of 3 ATP • 2 electrons from FADH2 produce a max of 2 ATP

16. Electrochemical Proton Gradient

17. ETC Summary • NADH e- transferred to O2; three proton pumps activated • FADH2 e- transferred to O2; two proton pumps activated • electrochemical proton gradient formed across IMM

18. Electron Transport Chain Animation ETC Animation

19. Oxidative Phosphorylation

20. Proton Motive Force: Chemiosmosis The electrochemical gradient (chemiosmosis) produced by the ETC can now be used to generate ATP through the process of oxidative phosphorylation (OXPHOS). OXPHOS occurs through the enzyme complex ATP synthase. OXPHOS Animation

21. ATP Synthase Complex Two components: • proton channel / rotor embedded in IMM • catalytic sites that phosphorylate ADP to ATP This is an example of facilitated diffusion (passive transport)

22. ATP Production oxidative phosphorylation - ATP is produced as protons flow through ATP synthase. In general: • 1 NADH  2.5 – 3 ATP molecules • 1 FADH2  1.5 – 2 ATP molecules The ETC is coupled with ATP synthesis. The latter is dependent on the former.

23. ATP Production Glycolysis Oxidative Decarboxylation Krebs Cycle

24. ATP Production– Aerobic Respiration

25. Why 36-38 ATP?

26. Electron shuttles span membrane MITOCHONDRION CYTOSOL 2 NADH or 2 FADH2 2 FADH2 2 NADH 2 NADH 6 NADH Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle 2 Acetyl CoA 2 Pyruvate Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol by substrate-level phosphorylation by substrate-level phosphorylation About 36 or 38 ATP Maximum per glucose: Figure 9.16