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Ch.9 Cellular Respiration

Ch.9 Cellular Respiration. A.P. Biology. What’s the point?. The point is to make ATP !. ATP. 2006-2007. Harvesting stored energy. glucose + oxygen  energy + water + carbon. dioxide. respiration. ATP. +. 6H 2 O. +. 6CO 2. + heat. . C 6 H 12 O 6. +. 6O 2.

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Ch.9 Cellular Respiration

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  1. Ch.9Cellular Respiration A.P. Biology

  2. What’s thepoint? The pointis to makeATP! ATP 2006-2007

  3. Harvesting stored energy glucose + oxygen  energy + water + carbon dioxide respiration ATP + 6H2O + 6CO2 + heat  C6H12O6 + 6O2 COMBUSTION = making a lot of heat energy by burning fuels in one step ATP fuel(carbohydrates) glucose O2 O2 RESPIRATION = making ATP (& some heat)by burning fuels in many small steps ATP enzymes CO2 + H2O + ATP (+ heat) CO2 + H2O + heat • Glucose is the model • catabolism of glucose to produce ATP

  4. How do we move electrons in biology? e p loses e- gains e- oxidized reduced + – + + H oxidation reduction H  C6H12O6 + 6O2 6CO2 + 6H2O + ATP H oxidation • Moving electrons in living systems • electrons cannot move alone in cells • electrons move as part of H atom • move H = move electrons reduction e-

  5. How do we harvest energy from fuels? + + oxidation reduction e- loses e- gains e- oxidized reduced + – e- e- • Digest large molecules into smaller ones • break bonds & move electrons from one molecule to another • as electrons move they “carry energy” with them • that energy is stored in another bond, released as heat or harvested to make ATP redox

  6. Oxidation & reduction oxidation  C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction • Oxidation • adding O • removing H • loss of electrons • releases energy • exergonic • Reduction • removing O • adding H • gain of electrons • stores energy • endergonic

  7. like $$in the bank Moving electrons in respiration O– O– O– O– P P P P –O –O –O –O O– O– O– O– O O O O NAD+ nicotinamide Vitamin B3 niacin O O H H C C NH2 C C NH2 How efficient! Build once,use many ways N+ N+ reduction + H oxidation phosphates adenine ribose sugar reducing power! NADH H • Electron carriers move electrons by shuttling H atoms around • NAD+NADH (reduced) • FAD+2FADH2 (reduced) carries electrons as a reduced molecule

  8. Cellular respiration: overview 1.Glycolysis: cytosol (cytoplasm); degrades glucose into pyruvate 2.Kreb’s Cycle: mitochondrial matrix; pyruvate into carbon dioxide 3.Electron Transport Chain: inner membrane of mitochondrion; electrons passed to oxygen

  9. What’s thepoint? The pointis to makeATP! ATP 2006-2007

  10. Glycolysis glucose      pyruvate 6C 3C 2x In thecytosol?Why doesthat makeevolutionarysense? That’s not enoughATP for me! • Breaking down glucose • “glyco – lysis” (splitting sugar) • it’s inefficient • generate only2 ATP for every 1 glucose

  11. Evolutionary perspective Enzymesof glycolysis are“well-conserved” You meanwe’re related?Do I have to invitethem over for the holidays? • Prokaryotes • first cells had no organelles • Anaerobic atmosphere • life on Earth first evolved withoutfree oxygen (O2) in atmosphere • energy had to be captured from organic molecules in absence of O2 • Prokaryotes that evolved glycolysis are ancestors of all modern life • ALL cells still utilize glycolysis

  12. Overview enzyme enzyme enzyme enzyme enzyme enzyme enzyme enzyme ATP ATP 2 4 4 2 2 ADP ADP NAD+ 2Pi 2 2H 2Pi glucose C-C-C-C-C-C fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P pyruvate C-C-C DHAP = dihydroxyacetone phosphate G3P = glyceraldehyde-3-phosphate 10 reactions • convert glucose (6C)to 2 pyruvate (3C) • produces:4 ATP & 2 NADH • consumes:2 ATP • net yield:2 ATP & 2 NADH

  13. Is that all there is? O2 O2 O2 O2 O2 3C 2x glucose     pyruvate 6C Hard wayto makea living! • Not a lot of energy… • for 1 billon years+ this is how life on Earth survived • no O2 = slow growth, slow reproduction • only harvest 3.5% of energy stored in glucose • more carbons to strip off = more energy to harvest

  14. But can’t stop there! DHAP G3P NAD+ Pi NAD+ Pi NADH NADH 1,3-BPG 1,3-BPG Pi Pi NAD+ NAD+ 6 NADH NADH 7 ADP ADP ATP ATP 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) 8 2-Phosphoglycerate (2PG) 2-Phosphoglycerate (2PG) 9 H2O H2O Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) 10 ADP ADP ATP ATP Pyruvate Pyruvate raw materialsproducts Glycolysis glucose + 2ADP + 2Pi + 2 NAD+2pyruvate+2ATP+2NADH • Going to run out of NAD+ • without regenerating NAD+,energy production would stop! • another molecule must accept H from NADH • so NAD+ is freed up for another round

  15. Pyruvate is a branching point O2 O2 fermentation anaerobicrespiration mitochondria Krebs cycle aerobic respiration Pyruvate

  16. How is NADH recycled to NAD+? recycleNADH without oxygen anaerobic respiration “fermentation” with oxygen aerobic respiration pyruvate NAD+ H2O CO2 NADH NADH O2 acetaldehyde NADH acetyl-CoA NAD+ NAD+ lactate lactic acidfermentation which path you use depends on who you are… Krebs cycle ethanol alcoholfermentation Another molecule must accept H from NADH

  17. Fermentation (anaerobic) pyruvate  ethanol + CO2 3C 2C 1C pyruvate  lactic acid NADH NADH NAD+ NAD+ 3C 3C back to glycolysis • beer, wine, bread • Animals, some fungi back to glycolysis • cheese, anaerobic exercise (no O2) Plants, bacteria, yeast

  18. Alcohol Fermentation pyruvate  ethanol + CO2 3C 2C 1C NADH NAD+ recycleNADH bacteria yeast back to glycolysis • Dead end process • at ~12% ethanol, kills yeast • can’t reverse the reaction

  19. Lactic Acid Fermentation O2 pyruvate  lactic acid NADH NAD+ 3C 3C recycleNADH animalssome fungi  back to glycolysis • Reversible process • once O2 is available, lactate is converted back to pyruvate by the liver Count thecarbons!

  20. Pyruvate is a branching point O2 O2 fermentation anaerobicrespiration mitochondria Krebs cycle aerobic respiration Pyruvate

  21. Glycolysis is only the start glucose      pyruvate 6C 3C 2x pyruvate       CO2 3C 1C • Glycolysis • Pyruvate has more energy to yield • 3 more C to strip off (to oxidize) • if O2 is available, pyruvate enters mitochondria • enzymes of Krebs cycle complete the full oxidation of sugar to CO2

  22. Oxidation of pyruvate [ ] 2x pyruvate  acetyl CoA + CO2 NAD 1C 3C 2C Wheredoes theCO2 go? Exhale! • Pyruvate enters mitochondrial matrix • 3 step oxidation process • releases 2 CO2(count the carbons!) • reduces 2NAD  2 NADH (moves e-) • produces 2acetyl CoA • Acetyl CoA enters Krebs cycle

  23. Krebs cycle 1937 | 1953 Hans Krebs 1900-1981 • aka Citric Acid Cycle • in mitochondrial matrix • 8 step pathway • each catalyzed by specific enzyme • step-wise catabolism of 6C citrate molecule • Evolved later than glycolysis • does that make evolutionary sense? • bacteria 3.5 billion years ago (glycolysis) • free O22.7 billion years ago (photosynthesis) • eukaryotes 1.5 billion years ago (aerobic respiration = organelles  mitochondria)

  24. 2C 6C 5C 4C 3C 4C 4C 4C 4C 6C CO2 CO2 Count the carbons! pyruvate acetyl CoA citrate oxidationof sugars This happens twice for each glucose molecule x2

  25. 2C 6C 5C 4C 3C 4C 6C 4C 4C 4C NADH ATP CO2 CO2 CO2 NADH NADH FADH2 NADH Count the electron carriers! pyruvate acetyl CoA citrate reductionof electroncarriers This happens twice for each glucose molecule x2

  26. Energy accounting of Krebs cycle 4 NAD+1 FAD 4 NADH+1FADH2 2x 1C 3x 1 ADP 1 ATP pyruvate          CO2 3C ATP Net gain = 2 ATP = 8 NADH + 2 FADH2

  27. ATP accounting so far… Glycolysis 2ATP Kreb’s cycle 2ATP Life takes a lot of energy to run, need to extract more energy than 4 ATP! There’s got to be a better way! I need a lotmore ATP! A working muscle recycles over 10 million ATPs per second

  28. Whassup? So we fully oxidized glucose C6H12O6  CO2 & ended up with 4 ATP! What’s the point?

  29. H+ H+ H+ H+ H+ H+ H+ H+ H+ Electron Carriers = Hydrogen Carriers • Krebs cycle produces large quantities of electron carriers • NADH • FADH2 • go to Electron Transport Chain! ADP+ Pi ATP What’s so important about electron carriers?

  30. There is a better way! Electron Transport Chain series of proteins built into inner mitochondrial membrane along cristae transport proteins& enzymes transport of electrons down ETC linked to pumping of H+ to create H+ gradient yields ~34 ATP from 1 glucose! only in presence of O2 (aerobic respiration) O2 Thatsounds morelike it!

  31. Remember the Electron Carriers? glucose Krebs cycle Glycolysis G3P 8 NADH 2 FADH2 2 NADH Time tobreak openthe piggybank!

  32. Electron Transport Chain e p 1 2 Building proton gradient! NADH  NAD+ + H intermembranespace H+ H+ H+ innermitochondrialmembrane H  e- + H+ C e– Q e– H e– FADH2 FAD H NADH 2H+ + O2 H2O NAD+ cytochromebc complex cytochrome coxidase complex NADH dehydrogenase mitochondrialmatrix

  33. Electron carriers pass electrons & H+ to ETC H cleaved off NADH & FADH2 electrons stripped from H atoms  H+ (protons) electrons passed from one electron carrier to next in mitochondrial membrane (ETC) flowing electrons = energy to do work transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space Stripping H from Electron Carriers H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ C e– Q e– 1 2 e– FADH2 FAD NADH 2H+ + O2 H2O NAD+ cytochromebc complex NADH dehydrogenase cytochrome coxidase complex H+ H+ H+ TA-DA!! Moving electronsdo the work! ADP+ Pi ATP

  34. H2O O2 But what “pulls” the electrons down the ETC? electronsflow downhill to O2 oxidative phosphorylation

  35. Electrons flow downhill Electrons move in steps from carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy make ATPinstead offire!

  36. We did it! Set up a H+ gradient Allow the protonsto flow through ATP synthase Synthesizes ATP ADP + PiATP H+ H+ H+ H+ H+ H+ H+ H+ ADP + Pi H+ “proton-motive” force ATP Are wethere yet?

  37. The diffusion of ions across a membrane build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP Chemiosmosis Chemiosmosis links the Electron Transport Chain to ATP synthesis So that’sthe point!

  38. Intermembrane space Pyruvate from cytoplasm Inner mitochondrial membrane H+ H+ Electron transport system C Q NADH e- H+ 2. Electrons provide energy to pump protons across the membrane. 1. Electrons are harvested and carried to the transport system. e- Acetyl-CoA NADH e- H2O e- Krebs cycle 3. Oxygen joins with protons to form water. 1 FADH2 O2 2 O2 + 2H+ H+ CO2 ATP H+ ATP ATP 4. Protons diffuse back indown their concentrationgradient, driving the synthesis of ATP. ATP synthase Mitochondrial matrix

  39. Taking it beyond… What is the final electron acceptor in Electron Transport Chain? H+ H+ H+ C e– Q e– 1 2 e– FADH2 FAD NADH 2H+ + O2 H2O NAD+ cytochromebc complex NADH dehydrogenase cytochrome coxidase complex O2 • So what happens if O2 unavailable? • ETC backs up • nothing to pull electrons down chain • NADH & FADH2 can’t unload H • ATP production ceases • cells run out of energy • and you die!

  40. What’s thepoint? The pointis to makeATP! ATP 2006-2007

  41. Review: Cellular Respiration Glycolysis: 2 ATP (substrate-level phosphorylation) Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6 ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose

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