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Chapter 9 Cellular Respiration: Harvesting Chemical Energy

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1 Chapter 9 Cellular Respiration: Harvesting Chemical Energy
高醫 生物醫學暨環境生物學系 助理教授 張學偉

2 powers most cellular work
Energy Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM CO2 + H2O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O2 ATP powers most cellular work Heat energy Figure 9.2

3 To keep working, cells must regenerate ATP
本圖補充

4 Oxidative phosphorylation: electron transport and chemiosmosis
An overview of cellular respiration Figure 9.6 Electrons carried via NADH Glycolysis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Oxidative Mitochondrion Cytosol

5 Concept 1: Catabolic pathways yield energy by oxidizing organic fuels
2: Glycolysis harvests energy by oxidizing glucose to pyruvate 3: The citric acid cycle completes the energy-yielding oxidation of organic molecules 4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis 5: Fermentation enables some cells to produce ATP without the use of oxygen 6: Glycolysis and the citric acid cycle connect to many other metabolic pathways

6 Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels

7 Catabolic Pathways and Production of ATP
Catabolic pathways (異化) yield energy by oxidizing organic fuels 同化作用 本圖為補充 exergonic (產能的) endergonic 耗能的

8 One catabolic process, fermentation (發酵)
Is a partial degradation of sugars that occurs without oxygen 稍後再講 Conecept 5: Fermentation enables some cells to produce ATP without the use of oxygen

9 Cellular respiration Is the most prevalent and efficient catabolic pathway Consumes oxygen (with O2 as the ultimate electron acceptor) and organic molecules such as glucose Yields ATP It is called cellular respiration to distinguish it from the respiration of breathing.

10 Redox Reactions: Oxidation and Reduction
Catabolic pathways yield energy Due to the transfer of electrons The Principle of Redox Redox reactions Transfer electrons from one reactant to another by oxidation and reduction

11 Definition of Oxidation & Reduction and its agent
In oxidation A substance loses electrons, or is oxidized In reduction A substance gains electrons, or is reduced Reducting Agent Oxidating Agent Na Cl Na Cl– becomes oxidized (loses electron) becomes reduced (gains electron)

12 Do not completely exchange electrons
Some redox reactions Do not completely exchange electrons Change the degree of electron sharing in covalent bonds 注意 : blue ball位置 CH4 H C O Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water + 2O2 CO2 Energy 2 H2O becomes oxidized becomes reduced Reactants Products Figure 9.3 注意 : blue ball位置

13 Oxidation of Organic Fuel Molecules During Cellular Respiration
- Glucose is oxidized in a series of steps and oxygen is reduced C6H12O6 + 6O CO2 + 6H2O + Energy becomes oxidized becomes reduced △G = Kcal △G < 0 spontaneous reaction (without an input of energy) Liberating energy

14 Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
NAD+ = Nicotinamide adenine dinucleotide NAD+ H O O– P CH2 HO OH N+ C NH2 N Nicotinamide (oxidized form) + 2[H] (from food) Dehydrogenase Reduction of NAD+ Oxidation of NADH 2 e– + 2 H+ 2 e– + H+ NADH Nicotinamide (reduced form) Figure 9.4 H+ Nucleotide = Base + Sugar + Phosphate Nucleosides = Sugar + Base (no phosphate) H+ adenine

15 Electrons from organic compounds
Are usually first transferred to NAD+, a coenzyme electron proton NAD+ H O O– P CH2 HO OH N+ C NH2 N Nicotinamide (oxidized form) + 2[H] (from food) Dehydrogenase Reduction of NAD+ Oxidation of NADH 2 e– + 2 H+ 2 e– + H+ NADH Nicotinamide (reduced form) Figure 9.4 H+ H+ Hydrogen atom 2 H  2H+ +2e- (oxidation) NAD+ + H+ +2e-  NADH (reduction) = NAD+ + 2H  NADH + H+

16 Ex. A  B + 2H+ +2e- (oxidation)
(+) FAD + 2H+ +2e-  FADH (reduction) = A+ FAD <=> B+ FADH2 A+ FAD <=> B+ FADH2 A+ NAD(P) <=> B+ NAD(P)H A is the electron donor (so it is oxidized) FAD & NAD(P) is the electron acceptor (so it is reduced). The products of the reaction are B (oxidized state) FADH2 or NAD(P)H (reduced state) .

17 圖形為補充 NADH passes the electrons to the electron transport chain

18 (a) Uncontrolled reaction
If electron transfer is not stepwise A large release of energy occurs As in the reaction of hydrogen and oxygen to form water (a) Uncontrolled reaction Free energy, G H2O Explosive release of heat and light energy Figure 9.5 A H2 + 1/2 O2

19 比較 The electron transport chain
(from food via NADH) 2 H e– 2 H+ 2 e– H2O Controlled release of energy for synthesis of ATP ATP Electron transport chain Free energy, G (b) Cellular respiration + Figure 9.5 B Passes electrons in a series of steps instead of in one explosive reaction Uses the energy from the electron transfer to form ATP

20 Oxidative phosphorylation: electron transport and chemiosmosis
An overview of cellular respiration Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Oxidative Mitochondrion Cytosol 3 1 2

21 Oxidative phosphorylation
Glycolysis Breaks down glucose into two molecules of pyruvate The citric acid cycle Completes the breakdown of glucose Oxidative phosphorylation Is driven by the electron transport chain Generates ATP

22 substrate-level phosphorylation
generate ATP from glycolysis and TCA cycle Figure 9.7 Enzyme ATP ADP Product Substrate P +

23 Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate
Means “splitting of sugar” Breaks down glucose into pyruvate Occurs in the cytoplasm of the cell

24 Energy investment phase
Glycolysis Citric acid cycle Oxidative phosphorylation ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 2 NAD+ + 4 e- + 4 H + 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Energy investment phase Energy payoff phase 4 ATP formed – 2 ATP used 2 NAD+ + 4 e– + 4 H + Glycolysis consists of two major phases Energy investment phase Energy payoff phase Figure 9.8 Net Rx Net Rx: Glucose + 2ADP+ 2Pi + NAD+ 2 Pyruvate + 2ATP + 2NADH + 2 H+

25 1, 3-Bisphosphoglycerate
investment phase payoff phase H OH HO CH2O O P CH2OH CH2 C CHOH ATP ADP Hexokinase Glucose Glucose-6-phosphate Fructose-6-phosphate Phosphoglucoisomerase Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase 1 2 3 4 5 Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate 2 NAD+ NADH 2 + 2 H+ Triose phosphate dehydrogenase P i P C CHOH O CH2 O– 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase 3-Phosphoglycerate Phosphoglyceromutase CH2OH H 2-Phosphoglycerate 2 H2O Enolase Phosphoenolpyruvate Pyruvate kinase CH3 6 8 7 9 10 Pyruvate Figure 9.8 Citric acid cycle Oxidative phosphorylation Glycolysis Kinase isomerase Mutase Aldolase enolase Dehydrogenase Figure 9.9 A

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28 Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules

29 The citric acid cycle Takes place in the matrix of the mitochondrion

30 Before citric acid cycle can begin
Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis CYTOSOL MITOCHONDRION NADH + H+ NAD+ 2 3 1 CO2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH3 O Transport protein O– Figure 9.10 Pyruvate Oxidation From Vit B

31 Oxidative phosphorylation
An overview of the citric acid cycle = TCA (Tricarboxyl acid) ATP 2 CO2 3 NAD+ 3 NADH + 3 H+ ADP + P i FAD FADH2 Citric acid cycle CoA Acetyle CoA NADH CO2 Pyruvate (from glycolysis, 2 molecules per glucose) Glycolysis Oxidative phosphorylation Figure 9.11 = Krebs Cycle

32 A closer look at the citric acid cycle
Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA a-Ketoglutarate Isocitrate Citric acid cycle S SH FADH2 FAD GTP GDP NAD+ ADP P i CO2 H2O + H+ C CH3 O COO– CH2 HO HC CH 1 2 3 4 5 6 7 8 Glycolysis Oxidative phosphorylation ATP Figure 9.12

33 A closer look at the citric acid cycle
Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA a-Ketoglutarate Isocitrate Citric acid cycle S SH FADH2 FAD GTP GDP NAD+ ADP P i CO2 H2O + H+ C CH3 O COO– CH2 HO HC CH 1 2 3 4 5 6 7 8 Glycolysis Oxidative phosphorylation ATP Figure 9.12 3C 2C pyruvate NAD + CoA NADH + CO2 4C 6C 6C ½ Glucose 4C Figure 9.12 4C 5C 4C 4C

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35 Energetics DHase

36 Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis

37 An overview of cellular respiration
Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Oxidative Mitochondrion Cytosol Figure 9.6 NADH and FADH2: Donate electrons to the electron transport chain (ETC), which powers ATP synthesis via oxidative phosphorylation

38 The Pathway of Electron Transport
H2O O2 NADH FADH2 FMN Fe•S O FAD Cyt b Cyt c1 Cyt c Cyt a Cyt a3 2 H + + 12 I II III IV Multiprotein complexes 10 20 30 40 50 Free energy (G) relative to O2 (kcl/mol) Figure 9.13 In the ETC Electrons from NADH and FADH2 lose energy in several steps At the end of the chain Electrons are passed to oxygen, forming water

39 Chemiosmosis: The Energy-Coupling Mechanism
ATP synthase is the enzyme that actually makes ATP INTERMEMBRANE SPACE 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 注意: H+& ATP的方向

40 At certain steps along the electron transport chain
Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space. [逆反應; 與產生ATP時的H+運送方向相反] 目的: resulting H+ gradient

41 The resulting H+ gradient
Stores energy Is referred to as a proton-motive force Drives chemiosmosis in ATP synthase Chemiosmosis Is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work

42 Chemiosmosis & electron transport chain
Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+ P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH+ FADH2 NAD+ FAD+ 2 H+ + 1/2 O2 H2O 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 synthase Q Oxidative phosphorylation Intermembrane space mitochondrial matrix Figure 9.15 NADH  3 ATP; FADH2  2 ATP

43 An Accounting of ATP Production by Cellular Respiration
Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH2 6 NADH Glycolysis Glucose 2 Pyruvate Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION 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

44 Shuttles for transfer of reducing equivalents
from cytosol into mitochondria 補充 不考 DHAP/GA3P shuttle Malate/Asp shuttle

45 Glycolysis  Pyruvate Oxidation  TCA
Glycolysis (aerobic) Glucose +2ADP + 2Pi+ 2NAD+ 2 pyruvate +2ATP+2NADH+2H++2H2O aerobic Pyruvate Oxidation 1 Pyruvate + NAD+ + CoASH  1 Acetyl-CoA + 1 NADH + CO2 2 Pyruvate + 2 NAD+ + 2 CoASH  2 Acetyl-CoA + 2 NADH + 2 CO2 TCA 2 Acetyl-CoA + 4 H2O + 6 NAD+ + 2FAD + 2GDP + 2 Pi  2 CO2 + 6 NADH + 2 FADH2 + 2 CoA-SH + 2 GTP Glycolysis  Pyruvate Oxidation  TCA 2 ATP 2 NADH (2H) 2 (2x1) GTP/ATP 6 (2x3) NADH 2 (2x1) FADH2 2 (2x1) NADH

46 Glycolysis  Pyruvate Oxidation  TCA
Glycolysis (aerobic) Glycolysis  Pyruvate Oxidation  TCA 2 ATP 2 NADH (2H) 2 (2x1) GTP/ATP 6 (2x3) NADH 2 (2x1) FADH2 2 (2x1) NADH NADH  3 ATP; FADH2  2 ATP EST & chemiosmosis ATP = 38 or (6) shuttle = 36 About 40% of the energy in a glucose molecule Is transferred to ATP during cellular respiration, making approximately 38 ATP

47 Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen

48 In the absence of oxygen [no cellular respiration]
Relies on oxygen to produce ATP In the absence of oxygen [no cellular respiration] Cells can still produce ATP through fermentation fermentation is a partial degradation of sugars that occurs without oxygen

49 Fermentation consists of
Glycolysis Can produce ATP with or without oxygen, in aerobic or anaerobic conditions Fermentation consists of Glycolysis + reactions that regenerate NAD+, which can be reused by glyocolysis

50 (a) Alcohol fermentation (b) Lactic acid fermentation
Types of Fermentation 2 ADP + 2 P1 2 ATP Glycolysis Glucose 2 NAD+ 2 NADH 2 Pyruvate 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 Lactate (b) Lactic acid fermentation H OH CH3 C O – O O– CO2 2 Figure 9.17 alcohol fermentation Pyruvate is converted to ethanol in two steps, one of which releases CO2 3C 2C lactic acid fermentation Pyruvate is reduced directly to NADH to form lactate as a waste product 3C 3C

51 Oxidative phosphorylation: electron transport and chemiosmosis
Anaerobic metabolism Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis Oxidative Mitochondrion Cytosol 3x2 2 2x2 lactate Or ethanol 1x2 32-34 2

52 Pyruvate is a key juncture in catabolism
Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18

53 Summaries of Glycolysis 1. anaerobic
Glucose -> 2 Lactate + 2 ATP (lactic acid fermentation) Glucose -> 2 Ethanol + 2 ATP (alcoholic fermentation) 2. aerobic Glucose -> 2 Pyruvate + 2ATP + 2NADH (aerobic subtotal) 註: 2 NADH -> 6 ATP (aerobic conversion: 氧化磷酸化)

54 Fermentation and Cellular Respiration Compared
相同點 Use glycolysis to oxidize glucose and other organic fuels to pyruvate 相異點 1.Differ in their final electron acceptor Fermentation by acetylaldehyde (ethanol ferment.); by pyruvate (lactate ferment.) Cellular Respiration by O2 2.Cellular respiration produces more ATP

55 The Evolutionary Significance of Glycolysis
Occurs in nearly all organisms Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

56 The Versatility of Catabolism
Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways The Versatility of Catabolism Catabolic pathways Funnel electrons from many kinds of organic molecules into cellular respiration

57 The catabolism of various molecules from food
Amino acids Sugars Glycerol Fatty Glycolysis Glucose Glyceraldehyde-3- P Pyruvate Acetyl CoA NH3 Citric acid cycle Oxidative phosphorylation Fats Proteins Carbohydrates Figure 9.19 b-oxidation

58 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

59 Regulation of Cellular Respiration via Feedback Mechanisms
Cellular respiration is controlled by allosteric enzymes (e.g., Phosphofructokinase) at key points in glycolysis and the citric acid cycle Allosteric regulation (see glossary) The binding of a molecule to a protein that affects the function of the protein at a different site. 補充圖

60 Fructose-1,6-bisphosphate
The control of cellular respiration Glucose Glycolysis Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Inhibits Pyruvate ATP Acetyl CoA Citric acid cycle Citrate Oxidative phosphorylation Stimulates AMP + Figure 9.20 ATP  AMP + ppi


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