Electron transport and chemiosmosis

1. Cellular Respiration: Stage 4 Electron transport and chemiosmosis

2. Review: Stages of Cellular Respiration • Glycolysis: occurs in cytosol. • Glucose  2 Pyruvate • 2 ATP • 2 NADH • Pyruvate Oxidation: occurs in matrix • 2 Pyruvate  2 acetyl-CoA • 2 NADH • Krebs Cycle: occurs in matrix • 2 acetyl-CoA  2 oxaloacetate (cycle) • 6 NADH • 2 FADH2 • 2 ATP

4. Stage 4: Electron Transport and Chemiosmosis • NADH and FADH2 eventually transfer their hydrogen atom electrons to series of compounds in the ETC. • Components of the ETC arranged in order of increasing electronegativity • Weakest attractor of electrons at beginning of chain • Strongest at the end.

5. How it works... • Each component is alternatively reduced and oxidized • Reduced: gains two electrons from component before it in the chain • Oxidized: by losing two electrons to component after it in the chain. • Like a baton being handed from runner to runner in a relay race.

6. As Electrons shuttle through the ETC... • Going from less stable to more stable • Therefore, energy is _____________. • This energy is used to move H+ ions from the matrix into intermembrane space. • Three proton pumps do this

7. At end of ETC... • Electrons very stable, therefore, extremely electronegative substance needed • _______________ strips two electrons from the final protein complex in the chain • Two protons added from matrix to form water. • Oxygen is the FINAL ELECTRON ACCEPTOR in the ETC.

8. Components of the ETC • NADH dehydrogenase • Ubiquinone (Q) (Mobile Electron Carrier) • Cytochrome b-cl complex • Cytochrome c (Mobile Electron Carrier) • Cytochromeoxidase complex

10. NADH gives up its two electrons to NADH dehydrogenase

11. Q and cytochrome c Shuttle electrons from one carrier to another

12. Electrons reach final protein complex in the chain • CytochromeOxidase Complex • Contains the enzyme cytochromeoxidase: catalyzes the reaction between the electrons, protons, and molecular oxygen to form _________.

14. Yeah...so? • That’s great. We’ve used NADH to pump H+ ions into the intermembrane space. • Where’s the ATP?

15. The Point of the ETC • Highly exergonic: _____________________ • Electrons: NADH  oxygen. (∆ G) of -222 kJ/mol NADH. • Free energy converted to electrochemical potential energy: • DUE TO THE PROTON GRADIENT FORMING ACROSS THE INNER MITOCHONDRIAL MEMBRANE.

16. Electrochemical Potential Energy • Type of energy stored by a battery • Caused by accumulation of charged objects (__________, __________, __________, etc.) • The energy becomes stored in the electrochemical gradient and will be used to power ATP synthesis in the next part of the process... ____________________________________

17. NADH vs. FADH2 • NADH passes electrons on to NADH dehydrogenase • Therefore, oxeach NADH molecule will help pump ________protons into the intermembrane space. • FADH2 passes electrons on to Q. • Help pump _________ protons.

18. NADH vs. FADH2 • NADH passes electrons on to NADH dehydrogenase • Therefore, oxidation of each NADH molecule will help pump ________protons into the intermembrane space. • RESULT: three ATP/coenzyme • FADH2 passes electrons on to Q. • Oxidation of FADH2 will help pump _________ protons. • RESULT: two ATP/coenzyme

19. Cytosolic NADH and Pyruvate Oxidation/Krebs NADH • Cytosolic NADH is produced by ___________. • May diffuse through outer membrane into intermembrane space. • Intermembrane is impermeable to NADH • Glycerol-phosphate shuttle: transfers electrons from cytosolic NADH to FAD to produce FADH2. • FADH2 transfers electrons to Q  ____ ATP.

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22. Cyanide • Cyanide inhibits cytochromeoxidaseactivity • This prevents _____________ from acting as the final electron acceptor • Shuts down the ETC, H+ pumps, and consequently, ATP production. • Coma  death • Not poisonous to all organisms! • MIT-13 (anaerobic bacteria) live on cyanide. Used in the same way as aerobes use oxygen.

23. Importance of Cristae • Allows multiple copies of the ETC to be located throughout inner membrane.

24. ... and finally... CHEMIOSMOSIS and OXIDATIVE ATP SYNTHESIS(but some terms first) TERMINOLOGY • Electrochemical Gradient: concentration gradient created by pumping ions into a space surrounded by a membrane that is impermeable to ions. • Proton-motive force (PMF): a force that moves protons through an ATPase complex on account of the electrochemical gradient of proteins across a biological membrane.

25. ETC forms an Electrochemical Gradient • Electrochemical gradient formed by ETC • Electrical component: higher positive charge in the _________________ space than the ________. • Chemical component: higher concentration of protons in the ____________space than the _____________. • Inner membrane impermeable to H+ ions. • Intermembranespace becomes H+ reservoir. • Potential difference (voltage) across inner mitochondrial membrane.

26. Electrochemical Gradient drives Chemiosomosis • Chemiosmosis: energy that drives synthesis of ATP comes from the “osmosis” of protons. • ____ forced to diffuse through protein channels associated with ATP synthase (ATPase). • Electrochemical gradient looses potential energy which is converted to chemical potential energy: ATP! • This energy drives the synthesis of ADP + Pi  ATP

27. Electrochemical Gradient and the Formation of ATP

28. Fate of ATP • ATP molecules transported through both mitochondrial _______________ by ____________ diffusion into the ____________ where they are used to drive ___________ processes such as movement, active transport, and synthesis reactions.

29. Relationship between ETC and Chemiosmosis? (review...) • Electron transport chain obtains electrons from hydrogen atoms from _________ and ____________ molecules. • At each sequential step in the ETC, electrons _________ energy by becoming more _____________. • Energy is harnessed by pumping _________ into the _____ reservoir. • ________________ gradient is formed, which forces _______ to diffuse back into the mitochondrial matrix via a __________ complex. • Energy of gradient is ____________, and that energy is used to create ATP from _____ and ____.

30. Conditions Necessary for ETC and Chemiosmosis This is a continuous process • H+ reservoir must be maintained  requires ____________ movement of __________ through the ETC  dependant on availability of ______________ to act as the final electron acceptor. • Hence, why we have lungs and fish have gills: _______________________. • Gas exchange in aerobic unicellular organisms? • Continuous source of electrons  electrons are transferred via _______ and _______  coenzymes are formed during the first ____ stages of cellular respiration  in the first three stages of cellular respiration, __________ is catabolized  need of glucose means a need of _________. • Hence, why heterotrophs must continually ____ and photoautotrophsmust continually ___________________.

31. Importance of Oxygen (in aerobes) • No chemical is electronegative enough to oxidize the last protein in the chain, except for oxygen. • If no oxygen  no substance to act as final electon acceptor  last protein can not be ‘freed up,’  ETC shuts down  FADH2 and NADH can no longer be oxidized  no NAD+ or FAD to recycle back into steps 1, 2 and 3.

32. Substrate-level vs. Oxidative Phosphorylation Substrate-level Phosphorylation Occurs in Glycolysis • 2 ATP in step 7 and 2 ATP in step 10 • Oxidative Phosphorylation • Occur in • Pyruvate oxidation • Krebs cycle • Electron transport & Chemiosmosis

34. The Exergonic Flow of Electrons in Aerobic Respiration What’s happening to the ‘lost’ energy?

35. THE ENERGETICS OF OXIDATIVE PHOSPHORYLATION (1) • Water can be formed in a test tube by combining hydrogen gas and oxygen gas. • Explosive reaction: bonding electrons move closer to a nucleus in water than in their reactant molecules. • But... Water is formed at the end of the ETC... WHY DON’T WE BLOW UP!?

36. THE ENERGETICS OF OXIDATIVE PHOSPHORYLATION (2) • Electrons moving through the ETC occupying more _______________ configurations as they move to ever more ___________ components. • Energy is ______________ at each step. • Therefore, electrons in a very ____________ state at the end of the ETC. Electrons gain more _____________ when captured by oxygen. • Resulting formation of water is a low-energy emitting process.

37. THE ENERGETICS OF OXIDATIVE PHOSPHORYLATION (3)

38. ETC Videos http://www.youtube.com/watch?v=_PgjsfY71AM

39. Seatwork/Homework • Read page 109 – 110 • Make notes and a diagram on the theoretical coenzyme and ATP yield. This is for YOU to study from! Answer the following questions: • The theoretical yield of ATP is 36. Give two reasons why the actual yield may differ from this. • What is the estimated number of ATP molecules formed for each glucose molecule? • Read the section on “Efficiency of Energy Conversion...” Answer the following questions: • 1) How is the efficiency of aerobic respiration calculated? • 2) How does the efficiency of aerobic respiration differ from glycolysis?

40. Seatwork/Homework Read the section “Metabolic Rate.” Make notes and answer the following questions: • What is metabolic rate? • What is BMR? For humans, how much energy does the BMR account for ? • What are some factors that effect the BMR? • What is a Benzinger calorimeter? Briefly, how does it work? (skip the calculation)

41. Seatwork/Homework Read the section on “Controlling Aerobic Respiration.” Answer the following questions: • What is phosphofructokinase? How does it regulate aerobic respiration? (in terms of ADP, ATP, and citrate). • How do NADH levels regulate respiration?