STAGE 4: ELECTRON TRANSPORT and CHEMIOSMOSIS

1. STAGE 4:ELECTRON TRANSPORTandCHEMIOSMOSIS

2. Electron Transport Chain (ETC) • series of compounds, mainly proteins, which are associated with the inner mitochondrial membrane • arranged in order of increasing electronegativity: • NADH dehydrogenase < ubiquinone < cytochrome b-c1 complex < cytochrome c <cytochrome oxidase complex

3. Electron Transport Chain (ETC) • Textbook p. 105

4. Electron Transport Chain (ETC) • Each component is alternately a. reduced (gaining two electrons from the component before it in the chain) b. oxidized (losing two electrons to the component after it in the chain)

5. Electron Transport Chain (ETC) • Most of the energy produced during the Kreb’s cycle is held in energy carriers such as NADH and FADH2that stay within the mitochondrial matrix. • They transfer their high energy electrons to proteins on the inner membrane of the mitochondrion.

6. Electron Transport Chain (ETC) • Physical Characteristics: - inner mitochondrial membrane separates the matrix from the outer compartment - large proteins embedded in inner membrane - these proteins are the electron carriersin the electron transport chain (ETC) - electron carriers arrayed side by side like the links in the chain - 3 of the proteins are called ion pumps

7. Electron Transport Chain (ETC) • There are 9 quicks steps that occur in the electron transport chain:

8. Electron Transport Chain (ETC) (1)NADH transfers two high energy electrons to the first electron carrier: an ion pump. (2)NADH changes to NAD+. (3) The carrier protein uses energy from the electrons to pump two H+ ions from the matrix into the outer compartment.

9. Electron Transport Chain (ETC) (4) The electrons are then passed to the next protein in the chain and then on to the third electron carrier. (5) This third protein is also an ion pump. It uses a bit more of the electron’s energy to pump two H+ ions through the membrane. (6) The electrons shift again to the fourth protein then to the fifth. This protein is a third ion pump.

10. Electron Transport Chain (ETC) (7) Using energy from the electrons, the protein pumps two more H+ ions into the outer compartment. (8) The two electrons are now much lower in energy. They combine with twoH+ ions and an oxygen atom. Oxygen, absorbed from air during inhalation is the final electron acceptorat the end of the electron transport chain (ETC) (9) A molecule of water (H2O) is formed.

11. Electron Transport Chain (ETC) PATHS: - NADH gives up 2 electrons to the first ETC complex: NADH dehydrogenase. - Q and cytochromec (mobile electron carriers) shuttle the electrons from one protein to the next until they reach the final protein complex in the chain: cytochromeoxidase complex - the enzyme cytochromeoxidase complex catalyzes (speeds up) the reaction between the electrons, protons and molecular oxygen to form water

12. Electron Transport Process • highly exergonic (energy of the products is less than the energy of the reactants) • free energy lost by the electron pair during electron transport is used to pump 3 protons into the intermembrane space • converts one form of energy into another: chemical potential energy of electron position  electrochemical potential energy of a proton gradient that forms across the inner mitochondrial membrane

13. Three main points • Electrochemical potential energy • Important to distinguish between NADH and FADH2 in terms of their relationship with the electron transport system • A distinction must be made between the NADH molecules produced in glycolysis and those produced in the pyruvate oxidation& Krebs cycle.

14. Electrochemical Potential Energy - Stored energy possessed by a charged battery - NADH -> oxygen, free energy (-222kJ/mol) - Stored and will be used to power ATP synthesis (chemiosmosis)

15. NADH and FADH2 in the electron transport system - NADH passes its electrons on to the 1st protein complex (NADH dehydrogenase) - FADH2 transfers its electrons to Q, the second component of the chain - The free energy released by the oxidation of FADH2 is used to pump 2 protons into the intermembrane space, while NADH pumps 3

16. A distinction between the NADH molecules - The NADH molecules produced in glycolysis and those produced in the pyruvate oxidation& Krebs cycle are different - NADH(glycolysis) in the cytoplasm may diffuse through the outer mitochondrial membrane into the intermembrane space.

17. 2 Shuttle Systems - Glycerol-phosphate shuttle -> transfers the electrons from cystolic NADH to FAD to produce FADH2 and 2 ATP molecules(chemiosmosis) - Aspartateshuttle -> transfers electrons to NAD+ instead of FAD, forming NADH, and then three ATP molecules

18. - The many folds of the inner membrane increase surface area & allow multiple copies of the ETC - A limited number of NAD+ and FAD molecules -> recycled - The resulting oxidized compounds pick up more hydrogen atoms in glycolysis, pyruvate oxidation, or the Krebs cycle

19. Chemiosmosis and Oxidative ATP Synthesis • Chemiosmosis: a process for synthesizing ATP using the energy of an electrochemical gradient and the ATP synthase enzyme

20. The protons that accumulate in the intermembrane space of the mitochondion during electron transport create an electrochemical gradient that stores free energy • Electrochemical gradient: a concentration gradient created by pumping ions into a space surrounded by a membrane that is impermeable to the ions.

21. The free energy stored in the electrochemical gradient produces a proton-motive force(PMF) that moves protons through an ATPase complex • The energy of the gradient is reduced as the protons pass through the ATPase complex back into the mitochondrial matrix

22. Proton-motive force(PMF): a force that moves protons through an ATPase complex on account of the free energy stored in the form of an electrochemical gradient of protons across a biological membrane • ATPase: a catalyst for the synthesis of ATP from ADP and inorganic phosphate in the matrix • Electron transport followed by chemiosmosis is the last stage of the oxidative phosphorylation process

23. What Happens When it stops? • No food(glucose) = no electrons • Heterotrophs must keep eating • Autotrophs must keep photosynthesizing

24. No O2 = no flow of electrons in ETC since O2 is final electron acceptor, freeing up the pathway • There’s no chemical in body Electronegative enough to oxidize last protein, O2 used to free protein

25. H+ not pumped and the concentration becomes even between matrix and intermembrane space • Chemiosomosis and ATP manufacturing stops

26. As for NADH and FADH2… • ETC clogged since O2 isn’t there to take away the final electron, holding up the entire production line • NADH and FADH2 can’t give up their electrons, and remain in their reduced form unable to oxidize H from other glucose

27. Dependancy • Pyruvate Oxidation, Kreb’s Cycle, ETC and chemiosmosis are linked and all depend on glycolysis for pyruvate • ETC and chemiosmosis BOTH depend on O2 and electrons to function, in this way they are coupled

28. Electron Transport Chain (ETC) • http://www.youtube.com/watch?v=kN5MtqAB_Yc&feature=related