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Electron transport and chemiosmosis
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  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

  3. 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.

  4. 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.

  5. 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

  6. 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.

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

  8. NADH gives up its two electrons to NADH dehydrogenase

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

  10. 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 _________.

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

  12. 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.

  13. 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... ____________________________________

  14. 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.

  15. 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

  16. 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.

  17. YazeedEssa Guilty… by Michael Small | March 5, 2010 at 02:29 pm YazeedEssa, an Ohio Doctor, Has Been Found Guilty of Murdering His Wife with Cyanide Poison YazeedEssa was convicted of murder on Friday, March 5th. The Ohio doctor was found guilty of lacing his wife's calcium pills with cyanide so that he could be with his mistress. Essa fled to Lebanon after his wife's death, but gave up an extradition fight and returned to Ohio to face trial. YazeedEssa Guilty: Doctor Murdered Wife with Cyanide | NowPublic News Coveragehttp://www.nowpublic.com/world/yazeed-essa-guilty-doctor-murdered-wife-cyanide-2587107.html#ixzz1FGGtO1QF

  18. 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.

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

  20. ... 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.

  21. 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.

  22. 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

  23. Electrochemical Gradient and the Formation of ATP

  24. 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.

  25. 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 ____.

  26. 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 ___________________.

  27. 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.

  28. 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

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

  30. 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!?

  31. 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.


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

  34. 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?

  35. 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)

  36. 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?