1. THIRD STAGE OF AEROBIC RESPIRATION- A BIG ENERGY PAYOFF Chapter 8.4 AP Biology Fall 2010

2. Electron Transfer Phosphorylation Coenzymes donate electrons to electron transfer chains in the inner mitochondrial membrane Flow of electrons through chains drives attachment of phosphate to ADP molecules That is what electron transfer phosphorylation means

3. Electron Transfer Phosphorylation Incremental energy release is more efficient Two NADH that formed in the cytoplasm (glycolysis) cannot directly reach the ATP forming machinery Must give up electrons and hydrogen to transport proteins, which shuttle them across the inner membrane into the innermost compartment NAD+ or FAD pick them up Eight NADH and two FADH2 from the second stage are already inside

4. Electron Transfer Phosphorylation Coenzymes turn over electrons to transfer chains Coenzymes give up hydrogen, which now has a positive charge (H+) Electrons lose a bit of energy through chain At three transfers, that energy drives pumping of H+ into the outer compartment H+ ions accumulate Sets up concentration and electrical gradients across inner membrane

5. Electron Transfer Phosphorylation H+ cant cross lipid bilayer Follows its gradients by flowing through ATP synthases ATP synthases changes shape, promotes attachment of unbound phosphate to ADP forming ATP

6. Electron Transfer Phosphorylation Last phase of electron transfer chain is passing electrons to oxygen Combines with H+ and forms water Oxygen is final acceptor of electrons originally stripped from glucose

7. Electron Transfer Phosphorylation Oxygen starved cells: Electrons have no where to go Chain backs up with electrons all the way to NADPH No H+ gradient forms, no ATP forms Without oxygen, cell of complex organisms do not survive long

8. Electron Transfer Phosphorylation: In Summary NADH and FADH2 give up their electrons to transfer (enzyme) systems embedded in the mitochondrial inner membrane The energy is used to pump hydrogen ions out of the inner compartment When hydrogen ions flow back through the ATP synthases in the channels, the coupling of Pi to ADP yields ATP

9. Summing Up: The Energy Harvest Electron transfer yields 32 ATPs Glycolysis yields 2 ATPs Krebs yields 2 ATPs Total = 36 ATPs per glucose molecule Anaerobic pathways may use up to 18 glucose molecules to get the same results

10. Summing Up: The Energy Harvest Normally, for every NADH produced within the mitochondria and processed by the electron transfer chain Three ATP are formed FADH2 yields two ATPs

11. Summing Up: The Energy Harvest In most cells (skeletal, brain), NADH from the cytoplasm cannot enter the mitochondrion and must transfer its electrons to FAD, yielding two ATP (for a total of 36) However in the liver, heart, and kidney cells, NAD+ accepts the electrons to yield 3 ATP 2 NADH Produced per glucose giving total of 38 ATP

14. Cellular Respiration

15. Review 1. T/FIncremental energy releases energy less efficiently 2. T/FElectron transfer occurs along the cell membrane 3. T/F32 ATPs are normally produced in the electron transport chain

16. Answer 1. False Incremental energy releases energy more efficiently 2. False Electron transfer occurs in the mitochondria (membrane) 3. True