Chapter 9~ Cellular Respiration: Harvesting Chemical Energy

1. Chapter 9~ Cellular Respiration: Harvesting Chemical Energy

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

3. Principles of Energy Harvest • Catabolic pathway √ Fermentation √Cellular Respiration C6H12O6 + 6O2 ---> 6CO2 + 6H2O + E (ATP + heat)

4. 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 glucose O2 O2 fuel(carbohydrates) Harvesting stored energy • Glucose is the model • catabolism of glucose to produce ATP RESPIRATION = making ATP (& some heat)by burning fuels in many small steps ATP enzymes CO2 + H2O + heat CO2 + H2O + ATP (+ heat)

5. + + oxidation reduction e- How do we harvest energy from fuels? • 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 loses e- gains e- oxidized reduced + – e- e- redox

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

7. oxidation  C6H12O6 + 6O2 6CO2 + 6H2O + ATP reduction Coupling oxidation & reduction • REDOX reactions in respiration • release energy as breakdown organic molecules • break C-C bonds • strip off electrons from C-H bonds by removing H atoms • C6H12O6 CO2 =thefuel has been oxidized • electrons attracted to more electronegative atoms • in biology, the most electronegative atom? • O2 H2O =oxygen has been reduced • couple REDOX reactions & use the released energy to synthesize ATP O2

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

9. like $$in the bank 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 Moving electrons in respiration • Electron carriers move electrons by shuttling H atoms around • NAD+NADH (reduced) • FAD+2FADH2 (reduced) reducing power! NADH H carries electrons as a reduced molecule

10. Oxidizing agent in respiration • NAD+ (nicotinamide adenine dinucleotide) • Removes electrons from food (series of reactions) • NAD + is reduced to NADH • Enzyme action: dehydrogenase • Oxygen is the eventual e- acceptor

11. Electron transport chains • Electron carrier molecules (membrane proteins) • Shuttles electrons that release energy used to make ATP • Sequence of reactions that prevents energy release in 1 explosive step • Electron route: food---> NADH ---> electron transport chain ---> oxygen

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

13. What’s thepoint? The pointis to makeATP! ATP

14. glucose      pyruvate 6C 3C 2x Glycolysis • Breaking down glucose • “glyco – lysis” (splitting sugar) • ancient pathway which harvests energy • where energy transfer first evolved • transfer energy from organic molecules to ATP • still is starting point for ALL cellular respiration • but it’s inefficient • generate only2 ATP for every 1 glucose • occurs in cytosol In thecytosol?Why doesthat makeevolutionarysense? That’s not enoughATP for me!

15. Evolutionary perspective Enzymesof glycolysis are“well-conserved” • 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 You meanwe’re related?Do I have to invitethem over for the holidays?

16. enzyme enzyme enzyme enzyme enzyme enzyme enzyme enzyme ATP ATP 4 2 4 2 2 ADP NAD+ ADP 2Pi 2 2H 2Pi Overview glucose C-C-C-C-C-C 10 reactions • convert glucose (6C)to 2 pyruvate (3C) • produces:4 ATP & 2 NADH • consumes:2 ATP • net yield:2 ATP & 2 NADH 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

17. Glycolysis summary endergonic invest some ATP ENERGY INVESTMENT -2 ATP G3P C-C-C-P exergonic harvest a little ATP & a little NADH ENERGY PAYOFF 4 ATP like $$in the bank • net yield • 2 ATP • 2 NADH NET YIELD

18. O- 9 H2O H2O enolase C O O C P Phosphoenolpyruvate (PEP) Phosphoenolpyruvate (PEP) CH2 O- 10 ADP ADP C O pyruvate kinase ATP ATP C O CH3 Pyruvate Pyruvate Substrate-level Phosphorylation • In the last steps of glycolysis, where did the P come from to make ATP? • the sugar substrate (PEP) • P is transferred from PEP to ADP • kinase enzyme • ADP  ATP ATP I get it! The Pi camedirectly fromthe substrate!

19. 2 ATP 2 ADP 2 NAD+ 4 ADP ATP 4 2 Energy accounting of glycolysis • Net gain = 2 ATP + 2 NADH • some energy investment (-2 ATP) • small energy return (4 ATP + 2 NADH) • 1 6C sugar 2 3C sugars glucose      pyruvate 6C 3C 2x All that work! And that’s all I get? Butglucose hasso much moreto give!

20. O2 O2 O2 O2 O2 3C 2x Is that all there is? • 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 glucose     pyruvate 6C Hard wayto makea living!

21. 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 But can’t stop there! raw materialsproducts • 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 Glycolysis glucose + 2ADP + 2Pi + 2 NAD+2pyruvate+2ATP+2NADH

22. recycleNADH How is NADH recycled to NAD+? without oxygen anaerobic respiration “fermentation” with oxygen aerobic respiration Another molecule must accept H from NADH 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

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

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

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

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

27. glucose      pyruvate 6C 3C 2x pyruvate       CO2 Glycolysis is only the start • 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 3C 1C

28. [ ] 2x pyruvate  acetyl CoA + CO2 NAD Oxidation of pyruvate • 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 1C 3C 2C Wheredoes theCO2 go? Exhale!

29. Krebs cycle 1937 | 1953 • 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) Hans Krebs 1900-1981

30. 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

31. 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

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

33. 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?

34. 4 NAD+1 FAD 4 NADH+1FADH2 2x 1C 3x 1 ADP 1 ATP Energy accounting of Krebs cycle Net gain = 2 ATP = 8 NADH + 2 FADH2 pyruvate          CO2 3C ATP

35. Value of Krebs cycle? • If the yield is only 2 ATP then how was the Krebs cycle an adaptation? • value of NADH & FADH2 • electron carriers & H carriers • reduced molecules move electrons • reduced molecules move H+ ions • to be used in the Electron Transport Chain like $$in the bank

36. Kreb’s Cycle: review • If molecular oxygen is present……. • Each pyruvate is converted into acetyl CoA (begin w/ 2): CO2 is released; NAD+ ---> NADH; coenzyme A (from B vitamin), makes molecule very reactive • From this point, each turn 2 C atoms enter (pyruvate) and 2 exit (carbon dioxide) • Oxaloacetate is regenerated (the “cycle”) • For each pyruvate that enters: 3 NAD+ reduced to NADH; 1 FAD+ reduced to FADH2 (riboflavin, B vitamin); 1 ATP molecule

37. 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

38. O2 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 ~36 ATP from 1 glucose! • only in presence of O2 (aerobic respiration) Thatsounds morelike it!

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

40. e p 1 2 Electron Transport Chain 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 What powers the proton (H+) pumps?…

41. Innermitochondrialmembrane Electron Transport Chain Intermembrane space C Q cytochromebc complex cytochrome coxidase complex NADH dehydrogenase Mitochondrial matrix

42. 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 Stripping H from Electron Carriers • 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 H+ H+ H+ TA-DA!! Moving electronsdo the work! ADP+ Pi ATP

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

44. 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!

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

46. Chemiosmosis • 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 links the Electron Transport Chain to ATP synthesis So that’sthe point!

47. Peter Mitchell 1961 | 1978 • Proposed chemiosmotic hypothesis • revolutionary idea at the time proton motive force 1920-1992

48. 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

49. H+ H+ H+ C e– Q e– 1 2 e– FADH2 FAD NADH 2H+ + O2 H2O NAD+ cytochromebc complex NADH dehydrogenase cytochrome coxidase complex Taking it beyond… • What is the final electron acceptor in Electron Transport Chain? 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!

50. What’s thepoint? The pointis to makeATP! ATP