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2 Cellular Respiration Harvesting Chemical Energy ATP

3 What’s the point? The point is to make ATP ! ATP

4 Harvesting stored energy Energy is stored in organic molecules – carbohydrates, fats, proteins Heterotrophs eat these organic molecules  food – digest organic molecules to get… raw materials for synthesis fuels for energy – controlled release of energy – “burning” fuels in a series of step-by-step enzyme-controlled reactions

5 Harvesting stored energy Glucose is the model – catabolism of glucose to produce ATP C 6 H 12 O 6 6O 2 ATP6H 2 O6CO 2  + ++ CO 2 + H 2 O + heat fuel (carbohydrates) combustion = making a lot of heat energy by burning fuels in one step respiration = making ATP (& some heat) by burning fuels in many small steps CO 2 + H 2 O + ATP (+ heat) ATP glucose glucose + oxygen  energy + water + carbon dioxide respiration O2O2 O2O2 + heat enzymes ATP

6 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 e-e- ++ e-e- +– loses e-gains e-oxidizedreduced oxidationreduction redox e-e-

7 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 p e + H + H +– loses e-gains e-oxidizedreduced oxidationreduction C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction H e-e-

8 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 – C 6 H 12 O 6  CO 2 = the fuel has been oxidized electrons attracted to more electronegative atoms – in biology, the most electronegative atom? – O 2  H 2 O = oxygen has been reduced – couple redox reactions & use the released energy to synthesize ATP C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction O2O2

9 Oxidation & reduction Oxidation – adding O – removing H – loss of electrons – releases energy – exergonic Reduction – removing O – adding H – gain of electrons – stores energy – endergonic C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction

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

11 Overview of cellular respiration 4 metabolic stages – Anaerobic respiration 1. Glycolysis – respiration without O 2 – in cytosol – Aerobic respiration – respiration using O 2 – in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain C 6 H 12 O 6 6O 2 ATP6H 2 O6CO 2  +++ (+ heat )

12 2006-2007 What’s the point? The point is to make ATP ! ATP

13 ATP synthase enzyme – H + flows through it conformational changes bond P i to ADP to make ATP – set up a H + gradient allow the H + to flow down concentration gradient through ATP synthase ADP + P i  ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP ADP P + But… How is the proton (H + ) gradient formed? And how do we do that?

14 2006-2007 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP Got to wait until the sequel! Got the Energy? Ask Questions! ADP P +

15 2006-2007 Cellular Respiration Harvesting Chemical Energy ATP

16 2006-2007 What’s the point? The point is to make ATP ! ATP

17 Harvesting stored energy Energy is stored in organic molecules – carbohydrates, fats, proteins Heterotrophs eat these organic molecules  food – digest organic molecules to get… raw materials for synthesis fuels for energy – controlled release of energy – “burning” fuels in a series of step-by-step enzyme-controlled reactions

18 Harvesting stored energy Glucose is the model – catabolism of glucose to produce ATP C 6 H 12 O 6 6O 2 ATP6H 2 O6CO 2  + ++ CO 2 + H 2 O + heat fuel (carbohydrates) combustion = making a lot of heat energy by burning fuels in one step respiration = making ATP (& some heat) by burning fuels in many small steps CO 2 + H 2 O + ATP (+ heat) ATP glucose glucose + oxygen  energy + water + carbon dioxide respiration O2O2 O2O2 + heat enzymes ATP

19 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 e-e- ++ e-e- +– loses e-gains e-oxidizedreduced oxidationreduction redox e-e-

20 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 p e + H + H +– loses e-gains e-oxidizedreduced oxidationreduction C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction H e-e-

21 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 – C 6 H 12 O 6  CO 2 = the fuel has been oxidized electrons attracted to more electronegative atoms – in biology, the most electronegative atom? – O 2  H 2 O = oxygen has been reduced – couple redox reactions & use the released energy to synthesize ATP C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction O2O2

22 Oxidation & reduction Oxidation – adding O – removing H – loss of electrons – releases energy – exergonic Reduction – removing O – adding H – gain of electrons – stores energy – endergonic C 6 H 12 O 6 6O 2 6CO 2 6H 2 OATP  +++ oxidation reduction

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

24 Overview of cellular respiration 4 metabolic stages – Anaerobic respiration 1. Glycolysis – respiration without O 2 – in cytosol – Aerobic respiration – respiration using O 2 – in mitochondria 2. Pyruvate oxidation 3. Krebs cycle 4. Electron transport chain C 6 H 12 O 6 6O 2 ATP6H 2 O6CO 2  +++ (+ heat )

25 2006-2007 What’s the point? The point is to make ATP ! ATP

26 ATP synthase enzyme – H + flows through it conformational changes bond P i to ADP to make ATP – set up a H + gradient allow the H + to flow down concentration gradient through ATP synthase ADP + P i  ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP ADP P + But… How is the proton (H + ) gradient formed? And how do we do that?

27 2006-2007 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP Got to wait until the sequel! Got the Energy? Ask Questions! ADP P +

28 10 reactions – convert glucose (6C) to 2 pyruvate (3C) – produces: 4 ATP & 2 NADH – consumes: 2 ATP – net: 2 ATP & 2 NADH 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 Overview ATP 2 ADP 2 ATP 4 ADP 4 NAD + 2 2 2Pi2Pi 2Pi2Pi 2H2H

29 2006-2007 Cellular Respiration Stage 2 & 3: Oxidation of Pyruvate Krebs Cycle

30 pyruvate       CO 2 Glycolysis is only the start Glycolysis Pyruvate has more energy to yield – 3 more C to strip off (to oxidize) – if O 2 is available, pyruvate enters mitochondria – enzymes of Krebs cycle complete the full oxidation of sugar to CO 2 2x2x 6C3C glucose      pyruvate 3C1C

31 Cellular respiration

32 intermembrane space inner membrane outer membrane matrix cristae Mitochondria — Structure Double membrane energy harvesting organelle – smooth outer membrane – highly folded inner membrane cristae – intermembrane space fluid-filled space between membranes – matrix inner fluid-filled space – DNA, ribosomes – enzymes mitochondrial DNA What cells would have a lot of mitochondria?

33 Mitochondria – Function What does this tell us about the evolution of eukaryotes? Endosymbiosis! Dividing mitochondria Who else divides like that? Advantage of highly folded inner membrane? More surface area for membrane- bound enzymes & permeases Membrane-bound proteins Enzymes & permeases Oooooh! Form fits function!

34 pyruvate    acetyl CoA + CO 2 Oxidation of pyruvate NAD 3C2C 1C [ 2x ] Pyruvate enters mitochondria – 3 step oxidation process – releases 1 CO 2 (count the carbons!) – reduces 2 NAD  2 NADH (moves e - ) – produces acetyl CoA Acetyl CoA enters Krebs cycle Where does the CO 2 go? Exhale!

35 Pyruvate oxidized to Acetyl CoA Yield = 2C sugar + NADH + CO 2 reduction oxidation Coenzyme A Pyruvate Acetyl CoA C-C-C C-C CO 2 NAD + 2 x []

36 Krebs cycle 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 O 2  2.7 billion years ago (photosynthesis) eukaryotes  1.5 billion years ago (aerobic respiration = organelles  mitochondria) 1937 | 1953 Hans Krebs 1900-1981

37 4C6C4C 2C6C5C4C CO 2 citrate acetyl CoA Count the carbons! 3C pyruvate x 2 oxidation of sugars This happens twice for each glucose molecule

38 4C6C4C 2C6C5C4C CO 2 citrate acetyl CoA Count the electron carriers! 3C pyruvate reduction of electron carriers This happens twice for each glucose molecule x2x2 CO 2 NADH FADH 2 ATP

39 So we fully oxidized glucose C 6 H 12 O 6  CO 2 & ended up with 4 ATP! Whassup? What’s the point?

40  Krebs cycle produces large quantities of electron carriers  NADH  FADH 2  go to Electron Transport Chain Electron Carriers = Hydrogen Carriers What’s so important about electron carriers? H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP ADP + P i

41 Energy accounting of Krebs cycle Net gain=2 ATP =8 NADH + 2 FADH 2 1 ADP1 ATP ATP 2x 4 NAD + 1 FAD4 NADH + 1 FADH 2 pyruvate          CO 2 3C 3x3x 1C

42 Value of Krebs cycle? If the yield is only 2 ATP then how was the Krebs cycle an adaptation? – value of NADH & FADH 2 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

43 2006-2007 What’s the point? The point is to make ATP ! ATP

44 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ And how do we do that? ATP But… Have we done that yet? ADP P + Set up a H + gradient – allow H + to flow through ATP synthase – powers bonding of P i to ADP ADP + P i  ATP

45 2006-2007 NO! The final chapter to my story is next! Any Questions?

46 2006-2007 Cellular Respiration Stage 4: Electron Transport Chain

47 Cellular respiration

48 2006-2007 What’s the point? The point is to make ATP ! ATP

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

50 There is a better way! Electron Transport Chain – series of molecules 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 O 2 (aerobic respiration) O2O2 That sounds more like it!

51 Mitochondria Double membrane – outer membrane – inner membrane highly folded cristae enzymes & transport proteins – intermembrane space fluid-filled space between membranes Oooooh! Form fits function!

52 Electron Transport Chain Intermembrane space Mitochondrial matrix Q C NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex Inner mitochondrial membrane

53 G3P Glycolysis Krebs cycle 8 NADH 2 FADH 2 Remember the Electron Carriers? 4 NADH Time to break open the bank! glucose

54 Electron Transport Chain intermembrane space mitochondrial matrix inner mitochondrial membrane NAD + Q C NADH H 2 O H+H+ e–e– 2H + +O2O2 H+H+ H+H+ e–e– FADH 2 1212 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e–e– H H  e- + H + NADH  NAD + + H H p e Building proton gradient! What powers the proton (H + ) pumps?…

55 H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ ATP NAD + Q C NADH H 2 O H+H+ e–e– 2H + +O2O2 H+H+ H+H+ e–e– FADH 2 1212 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e–e– Stripping H from Electron Carriers NADH passes electrons to ETC – H cleaved off NADH & FADH 2 – electrons stripped from H atoms  H + (protons) – electrons passed from one electron carrier to next in mitochondrial membrane (ETC) – transport proteins in membrane pump H + (protons) across inner membrane to intermembrane space ADP + P i TA-DA!! Moving electrons do the work!

56 But what “pulls” the electrons down the ETC? electrons flow downhill to O 2 oxidative phosphorylation O2O2

57 Electrons flow downhill Electrons move in steps from carrier to carrier downhill to O 2 – each carrier more electronegative – controlled oxidation – controlled release of energy make ATP instead of fire!

58 H+H+ ADP + P i H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ We did it! ATP Set up a H + gradient Allow the protons to flow through ATP synthase Synthesizes ATP ADP + P i  ATP Are we there yet? “proton-motive” force

59 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’s the point!

60 Peter Mitchell Proposed chemiosmotic hypothesis – revolutionary idea at the time 1961 | 1978 1920-1992 proton motive force

61 H+H+ H+H+ O2O2 + Q C 32 ATP 2 Pyruvate from cytoplasm Electron transport system ATP synthase H2OH2O CO 2 Krebs cycle Intermembrane space Inner mitochondrial membrane 1. Electrons are harvested and carried to the transport system. 2. Electrons provide energy to pump protons across the membrane. 3. Oxygen joins with protons to form water. 2H + NADH Acetyl-CoA FADH 2 ATP 4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP. Mitochondrial matrix 2 1 H+H+ H+H+ O2O2 H+H+ e-e- e-e- e-e- e-e-

62 Cellular respiration 2 ATP~2 ATP2 ATP~34 ATP +++ ~40 ATP

63 Summary of cellular respiration Where did the glucose come from? Where did the O 2 come from? Where did the CO 2 come from? Where did the CO 2 go? Where did the H 2 O come from? Where did the ATP come from? What else is produced that is not listed in this equation? Why do we breathe? C 6 H 12 O 6 6O 2 6CO 2 6H 2 O~40 ATP  +++

64  ETC backs up  nothing to pull electrons down chain  NADH & FADH 2 can’t unload H  ATP production ceases  cells run out of energy  and you die! Taking it beyond… What is the final electron acceptor in Electron Transport Chain? O2O2  So what happens if O 2 unavailable? NAD + Q C NADH H 2 O H+H+ e–e– 2H + +O2O2 H+H+ H+H+ e–e– FADH 2 1212 NADH dehydrogenase cytochrome bc complex cytochrome c oxidase complex FAD e–e–

65 2006-2007 What’s the point? The point is to make ATP ! ATP