1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 9 – Cellular Respiration Overview: Life Is Work Living cells – Require transfusions of energy from outside sources to perform their many tasks Assemble polymers Pump substances against the membrane Move Reproduce

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Respiration

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Basics of Respiration Biologists define respiration as the aerobic harvesting of energy from food molecules by cells

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels – Cells break down complex organic molecules (rich in potential energy) to simpler waste products (low in potential energy) To get energy to do work Rest is given off as heat

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cells do this in two ways: 1)Fermentation 2)Cellular respiration

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1) One catabolic process, fermentation – Is a partial degradation of sugars that occurs without oxygen

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2) Cellular respiration – Most prevalent and efficient catabolic pathway – Consumes oxygen and organic molecules such as glucose – Yields more ATP

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The equation for the reaction of cellular respiration: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy (ATP & Heat)

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Catabolic Pathways and Production of ATP The breakdown of organic molecules is exergonic – But catabolic pathways don’t do work directly Just release energy so work can be done

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Redox Reactions: Oxidation and Reduction Catabolic pathways yield energy – Due to the transfer of electrons – When 1 or more electrons transfers from one reactant to another the process is called oxidation reduction reaction or redox for short

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Principle of Redox Oxidation – loss of an electron – The substance that gives up its electron is the reducing agent Reduction the gain of an electron – The substance that gains the electron is the oxidizing agent

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Examples of redox reactions Na + Cl Na + + Cl – becomes oxidized (loses electron) Reducing agent becomes reduced (gains electron) Oxidizing agent

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Specifically in cellular respiration: C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes oxidized becomes reduced Glucose is oxidized and oxygen is reduced Electrons lose potential energy and energy is released

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings To Sum Up Remember an electron loses potential energy when it shifts from a less electronegative atom to a more electronegative atom (oxygen is very electronegative) So by oxidizing glucose, respiration frees stored energy (in glucose) and makes it available for work (as ATP)

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest via NAD + and the Electron Transport Chain Cellular respiration – Oxidizes glucose in a series of steps Because energy can’t be released all at once and still be useful

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest Glucose is broken down in a series of steps with the help of enzymes – First an electron is taken away from a glucose molecule. But a proton goes with the electron, so in effect a Hydrogen atom was removed – Second it is picked up by a coenzyme NAD + which will act as an oxidizing agent NAD + is reduced to NADH

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest – Second it is picked up by a coenzyme NAD + which will act as an oxidizing agent NAD + is reduced to NADH Electrons lose little potential energy going from food to NAD + NADH molecule now represents stored energy

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest – Third NADH will release their electrons down a series of reactions with oxygen being the final electron acceptor (or receptor) This is known as the Electron Transport Chain and uses the energy from the electron transfer to form ATP

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings To Sum Up: The electrons removed from food by NAD + fall down an energy gradient in the ETC to a far more stable location in the electronegative oxygen atom

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Stages of Cellular Respiration: A Preview – Glycolysis – The citric acid cycle – Oxidative phosphorylation

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The first two stages are catabolic pathways that decompose glucose 1) Glycolysis – Occurs in the cytosol – Breaks down glucose into two molecules of pyruvate 2) The citric acid cycle – Occurs in the mitochondrial matrix – Completes the breakdown of glucose

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Remember, why do we do this? Goal of cellular respiration is ATP production 1)Oxidative phosphorylation - redox rxns of the ETC 2)Substrate level phosphorylation

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Substrate level phosphorylation – ATP is formed directly Enzymes transfer a phosphate group from a substrate molecule to an ADP (adenosine diphosphate) – Generates ATP directly

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Both glycolysis and the citric acid cycle – Can generate ATP by substrate-level phosphorylation Figure 9.7 Enzyme ATP ADP Product Substrate P +

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of cellular respiration Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH 2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis ATP Substrate-level phosphorylation Oxidative phosphorylation Mitochondrion Cytosol

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate Glycolysis – Breaks down 1 glucose into 2 pyruvate – Occurs in the cytoplasm of the cell

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis consists of two major phases – Energy investment phase – Energy payoff phase Glycolysis Citric acid cycle Oxidative phosphorylation ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 P 2 NAD + + 4 e - + 4 H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Energy investment phase Energy payoff phase Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed – 2 ATP used 2 ATP 2 NAD + + 4 e – + 4 H + 2 NADH + 2 H + Figure 9.8

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A closer look at the energy investment phase – Be thinking: What do I start with? What do I add in to this? What do I get out of this? Where does this occur?

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

30. A closer look at the energy payoff phase – Be thinking: What do I start with? What do I add in to this? What do I get out of this? Where does this occur?

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

32. Citric Acid Cycle Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules The citric acid cycle – Takes place in the matrix of the mitochondrion

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Before the citric acid cycle can begin: – Pyruvate must first be converted to acetyl CoA, which links glycolysis to the citric acid cycle CYTOSOLMITOCHONDRION NADH + H + NAD + 2 31 CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O–O– O O C C CH 3 Figure 9.10 This only happens if oxygen is present!

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1)The carboxyl group is removed (it is fully oxidized so it has little chemical energy left) – First step where CO 2 is released CYTOSOLMITOCHONDRION NADH + H + NAD + 2 31 CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O–O– O O C C CH 3 Figure 9.10

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2) Electrons are removed and transferred to NAD + which stores them as NADH CYTOSOLMITOCHONDRION NADH + H + NAD + 2 31 CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O–O– O O C C CH 3 Figure 9.10

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3) Coenzyme A attaches via an unstable bond, so compound is now highly reactive CYTOSOLMITOCHONDRION NADH + H + NAD + 2 31 CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O–O– O O C C CH 3 Figure 9.10

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of the citric acid cycle ATP 2 CO 2 3 NAD + 3 NADH + 3 H + ADP + P i FAD FADH 2 Citric acid cycle CoA Acetyle CoA NADH + 3 H + CoA CO 2 Pyruvate (from glycolysis, 2 molecules per glucose) ATP Glycolysis Citric acid cycle Oxidative phosphorylatio n Figure 9.11

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A closer look at the citric acid cycle – Be thinking: What do I start with? What do I add in to this? What do I get out of this? Where does this occur?

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.12 Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA  -Ketoglutarate Isocitrate Citric acid cycle SCoA SH NADH FADH 2 FAD GTP GDP NAD + ADP P i NAD + CO 2 CoA SH CoA SH CoA S H2OH2O + H + H2OH2O C CH 3 O OCCOO – CH 2 COO – CH 2 HO C COO – CH 2 COO – CH 2 HCCOO – HOCH COO – CH CH 2 COO – HO COO – CH HC COO – CH 2 COO – CH 2 CO COO – CH 2 CO COO – 1 2 3 4 5 6 7 8 Glycolysis Oxidative phosphorylation NAD + + H + ATP Citric acid cycle Figure 9.12

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative Phosphorylation... ETC Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis So far, only 4 ATP have been made

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Pathway of Electron Transport Electron Transport Chain – is a collection of molecules embedded in the inner membrane of the mitochondria – Most components are proteins

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An NADH molecule begins the process by “dropping off” its electron at the first electron carrier molecule H2OH2O O2O2 NADH FADH2 FMN FeS O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H + + 1  2 I II III IV Multiprotein complexes 0 10 20 30 40 50 Free energy (G) relative to O 2 (kcl/mol) Figure 9.13

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Remember: each component will be reduced when it accepts the electron and oxidized when it passes the electron down to the more electronegative carrier molecule in the chain H2OH2O O2O2 NADH FADH2 FMN FeS O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H + + 1  2 I II III IV Multiprotein complexes 0 10 20 30 40 50 Free energy (G) relative to O 2 (kcl/mol) Figure 9.13

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Finally the electron is passed to oxygen, which is very electronegative. H2OH2O O2O2 NADH FADH2 FMN FeS O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H + + 1  2 I II III IV Multiprotein complexes 0 10 20 30 40 50 Free energy (G) relative to O 2 (kcl/mol) Figure 9.13 The oxygen also picks up 2 H + ions from the aqueous solution and forms water

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings FADH goes through mostly the same processes, except it drops off its electron at a lower point on the ETC H2OH2O O2O2 NADH FADH2 FMN FeS O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H + + 1  2 I II III IV Multiprotein complexes 0 10 20 30 40 50 Free energy (G) relative to O 2 (kcl/mol) Figure 9.13

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings WARNING: The ETC makes no ATP directly! The ETC releases energy in a step-wise series of reactions. It powers ATP synthesis via oxidative phosphorylation. But it needs to be coupled with chemiosmosis to actually make ATP.

47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis: The Energy-Coupling Mechanism Inner membrane of mitochondria has many protein complexes called ATP synthase – ATP synthase – enzyme that makes ATP from ADP and inorganic phosphate It uses the energy of an existing gradient to do this.

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The existing gradient is the difference in H + ion concentration on opposite sides of the inner membrane of the mitochondria Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+H+ H+H+ H+H+ H+H+ H+H+ ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H + + 1 / 2 O 2 H2OH2O ADP + Electron transport chain Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H + back across the membrane ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15

49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings So what is this process called? Chemiosmosis – the process in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work (like the synthesis of ATP)

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings It is the job of the ETC to create this H + ion gradient Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+H+ H+H+ H+H+ H+H+ H+H+ ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H + + 1 / 2 O 2 H2OH2O ADP + Electron transport chain Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H + back across the membrane ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15

51. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings H + ions are pumped into the intermembrane space by the ETC – The H + ions want to drift back into the matrix But they can only come into the matrix easily through ATP synthase channels

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The rushing of H + ions through ATP synthase acts like water turning a water wheel INTERMEMBRANE SPACE H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ P i + ADP ATP A rotor within the membrane spins clockwise when H + flows past it down the H + gradient. A stator anchored in the membrane holds the knob stationary. A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic Phosphate to ADP to make ATP. MITOCHONDRIAL MATRIX Figure 9.14 Result is that inorganic phosphate can be joined to ADP to make ATP

53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings To Sum Up Chemiosmosis is an energy coupling mechanism that uses energy stored in the form of a H + gradient across a membrane to drive cellular work In mitochondria, the energy for gradient formation comes from the exergonic redox reactions of the ETC and ATP synthesis is the work performed by ATP synthase

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis and the electron transport chain Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+H+ H+H+ H+H+ H+H+ H+H+ ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H + + 1 / 2 O 2 H2OH2O ADP + Electron transport chain Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H + back across the membrane ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15

55. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There is a problem though, when we try to account how much ATP is made from glucose (or any organic molecule) We can not state exactly how many ATP come from each glucose because of 3 reasons...

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 1)The ETC and ATP synthase work together, but not 100% in synchronicity So there isn’t an exact correlation between NADH (or FADH) and ATP production 1 NADH synthesizes 2.5 – 3.3 ATP ( 1 FADH synthesizes 1.5 – 2 ATP

57. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2) The electron shuttle into the mitochondria can vary (either NAD + or FAD) at the transition stage

58. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 3) The H + ion gradient does other things in the mitochondria, it is not just used for the synthesis of ATP

59. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bottom Line We’ll say there are 38 ATP: Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH 2 2 NADH 6 NADH 2 FADH 2 2 NADH Glycolysis Glucose 2 Pyruvate 2 Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol Maximum per glucose: About 36 or 38 ATP + 2 ATP + about 32 or 34 ATP or Figure 9.16

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An interesting note: Cellular respiration harvests about 40% of the energy in a glucose molecule – This is perhaps the most efficient energy conversion known

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In comparison: The most efficient cars only convert about 25% of the energy stored in gas into energy that moves the car

62. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen Cellular respiration – Relies on oxygen to produce ATP In the absence of oxygen – Cells can still produce ATP through fermentation – Not as much ATP is made

63. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis – Can produce ATP with or without oxygen, in aerobic or anaerobic conditions – Couples with fermentation – an extension of glycolysis, to produce ATP

64. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Fermentation Fermentation consists of – Glycolysis plus reactions that regenerate NAD +, which can be reused by glycolysis

65. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Type 1 In alcohol fermentation – Pyruvate is converted to ethanol in two steps, one of which releases CO 2 – The second regenerates NAD + so glycolysis can continue

66. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Type 2 During lactic acid fermentation – Pyruvate is reduced directly to NADH to form lactate as a waste product – No CO 2 is produced

67. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation and Cellular Respiration Compared Both fermentation and cellular respiration – Use glycolysis to oxidize glucose and other organic fuels to pyruvate

68. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fermentation and Cellular Respiration Contrasted Fermentation and cellular respiration – Differ in their final electron acceptor Cellular respiration – Produces more ATP

69. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvate is a key juncture in catabolism Glucose CYTOSOL Pyruvate No O 2 present Fermentation O 2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18 Some organisms can produce ATP using either cellular respiration or fermentation. They are called facultative anaerobes. Ex: our muscle cells

70. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways

71. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Versatility of Catabolism Catabolic pathways – Funnel electrons from many kinds of organic molecules into cellular respiration

72. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The catabolism of various molecules from food Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH 3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19

73. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Biosynthesis (Anabolic Pathways) The body – Uses small molecules to build other substances These small molecules – May come directly from food or through glycolysis or the citric acid cycle

74. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Regulation of Cellular Respiration via Feedback Mechanisms Cellular respiration – Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle