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Section 4. Fuel oxidation, generation of ATP

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  1. Section 4. Fuel oxidation, generation of ATP • Section 4. Overview of • Fuel oxidation, ATP generation: • Physiological processes require energy • transfer from chemical bonds in food: • Electrochemical gradient • Movement of muscle • Biosynthesis of complex molecules • 3 phases: • Oxidation of fuels (carbs, fats, protein) • Conversion of energy to ~PO4 of ATP • Utilization of ATP to drive energy-requiring reactions Fig.iv.1

  2. Fuel oxidation overview - respiration • Phase 1: energy (e-) from fuel transfer to NAD+ and FAD; • Acetyl CoA, TCA intermediates are central compounds • Phase 2: electron transport chain convert e- to ATP; • membrane proton gradient drives ATP synthase • Phase 3: ATP • powers processes Fig. iv.2

  3. Respiration occurs in mitochondria • Respiration occurs in mitochondria: • Most enzymes in matrix • Inner surface has • e- transport chain • ATP synthase • ATP transported through • inner membrane, • diffuses through outer • Some enzymes encoded • by mitochondrion genome, • most by nuclear genes Fig. iv.3

  4. Glucose is universal fuel for every cell • Glycolysis is universal fuel: • 1 glucose -> 2 pyruvate + 2 NADH + 2 ATP • Aerobic path: • Continued oxidation • Acetyl CoA -> TCA, • NADH, FAD(2H) -> e- transport chain • Lots of ATP • Anaerobic: fermentation: • ‘anaerobic glycolysis’ • Oxidation of NADH to NAD+ • Wasteful reduction of pyruvate • to lactate in muscles • to ethanol, CO2 by yeast Fig. iv.4

  5. Chapt. 19 Cellular bioenergetics of ATP, O2 • Ch. 19 Cellular bioenergetics • Student Learning Outcomes: • Explain the ATP-ADP cycle • Describe how chemical bond energy of fuels can do cellular work through ~PO4 bond of ATP • Explain how NADH, FAD(2H) coenzymes carry electrons to electron transport chain • Describe how ATP synthesis is endergonic (requires energy) • Describe how ATP hydrolysis (exergonic) powers biosynthesis, movement, transport

  6. Fuel oxidation makes ATP • Cellular Bioenergetics of ATP and O2: • Chemical bond energy of fuels transforms to physiological responses necessary for life • Fuel oxidation generates ATP • ATP hydrolysis provides energy for most work • High energy bonds of ATP: • Energy currency of cell Fig. 19.1

  7. ATP • High energy phosphate bond of ATP: • Strained phosphoanhydride bond • DG0’ -7.3 kcal/mol standard conditions • Hydrolysis of ATP to ADP + Pi transfers PO4 to metabolic intermediate or protein, for next step Fig. 19.2

  8. Thermodynamics brief • Thermodynamics states what is possible: • DG = change in Gibbs free energy of reaction: • DG = DG0 + RT ln [P]/[S] (R = gas const; T = temp oK) • DG0 = DG at standard conditions of1 M substrate & product and proceeding to equilibrium) • DG0’ = DG0under standard conditions of [H2O] = 55.5 M, • pH 7.0, and 25oC [37oC not much different] • Concentrations of substrate(s) and products(s): • At equilibrium, DG = 0, therefore • DG0’ = -RT lnKeq’ = -RT ln[P]/[S]

  9. Thermodynamics brief • Thermodynamics states what is possible: • Exergonic reactions give off energy (DG0’ < 0) • typically catabolic • Endergonic reactions require energy (DG0’ > 0) • typically anabolic • Unfavorable reactions are coupled to favorable reactions • Hydrolysis of ATP is very favorable • Additive DG0’ values determine overall direction

  10. C. Exogonic, endogonic reactions • Phosphoglucomutase converts G6P to/from G1P: • G6P to glycolysis • G1P to glycogen synthesis • Equilibrium favors G6P • Exergonic reactions give off energy (DG0’ < 0) • Endergonic reactions require energy (DG0’ > 0) Fig. 19.3

  11. III. Energy transformation for mechanical work • ATP hydrolysis can power muscle movement: • Myosin ATPase hydrolyzes ATP, changes shape • ADP form changes shape back, moves along • Actin was activated by Ca2+ Fig. 19.4

  12. ATP powers transport • Active transport: ATP hydrolysis moves molecules: • Na+, K+ ATPase sets up ion gradient; bring in items • Vesicle ATPases pump protons into lysosome • Ca2+-ATPases pump Ca2+ into ER, out of cell Fig. 10.6

  13. III. ATP powers biochemical work • ATP powers biochemical work, synthesis: • Anabolic paths require energy: DGo’ additive • Couple synthesis to ATP hydrolysis: • Phosphoryl transfer reactions • Activated intermediate • Ex. Table 19.3: • glucose + Pi -> glucose 6-P + H2O + 3.3 kcal/mol • ATP + H2O -> ADP + Pi - 7.3 kcal/mol • Sum: glucose + ATP -> glucose 6-P + ADP -4.0 • Also Glucose -> G-1-P will be -2.35 kcal/mol overall: • hydrolysis of ATP, through G-6-P to G-1-P

  14. Activated intermediates in glycogen synthesis • Glycogen synthesis needs 3 ~P: • Phosphoryl transfer to G6P • Activated intermediate with UDP covalently linked Fig. 19.5 Fig. 19.6

  15. DG depends on substrate, product concentrations • DG depends on substrate, product concentrations • DG = DG0 + RT ln [P]/[S] • Cells do not have 1M concentrations • High substrate can drive reactions with positive DG0’ • Low product (removal) can drive reactions with positive DG0’ • Ex., even though equilibrium (DG0’= +1.6 kcal/mol) • favors G6P: G1P in a ratio 94/6, • If G1P is being removed (as glycogen synthesis), then equilibrium shifts • ex. If ratio 94/3, then DG = -0.41 favorable

  16. Activated intermediates with ~bonds • Other compounds have high-energy bonds to aid biochemical work: (equivalent to ATP) • UTP, CTP and GTP also (made from ATP + NDP): • UTP for sugar biosyn, GTP for protein, CTP for lipids • Some other compounds: • Creatine PO4 energy reserve muscle, nerve, sperm • Glycolysis • Ac CoA TCA cycle Fig. 19.7

  17. V. Energy from fuel oxidation • Energy transfer from fuels through oxidative phosphorylation in mitochondrion: • NADH, FAD(2H) transfer e- to O2 • Stepwise process through • protein carriers • Proton gradient created • e- to O2 -> H2O • ATP synthase makes ATP • lets in H+ Fig. 19.8

  18. Oxidation/reduction • Oxidation: reduction reactions: • Electron donor gets oxidized; recipient is reduced • LEO GER: • Loss Electrons = oxidation; gain electrons is reduction • use coenzyme e- carriers Fig. 19.9 NADH Fig. 19.10 FAD(2H)

  19. Redox potentials • Redox potentials indicate energetic possibility: • Energy tower; combine half reactions for overall: • Ex. Table 19.4: • ½ O2 + 2H+ + 2e- -> H2O E0’ 0.816 • NAD+ + 2H+ + 2e- -> NADH + H+ -0.320 • Combine both reactions (turn NADH -> NAD+) = 0.320 • Total 1.136 (very big) = -53 kcal/mol • FAD(2H) gives less, since its only +0.20 (FAD(2H) -> FAD

  20. Calorie content of fuels reflects oxidation state • Calorie content of fuels reflects oxidation state: • C-H and C-C bonds will be oxidized: • Glucose has many C-OH already: • 4 kcal/g • Fatty acids very reduced: • 9 kcal/g • Cholesterol no calories: • not oxidized in reactions giving NADH

  21. Anaerobic glycolysis” = fermentation • ‘Anaerobic glycolysis’ = fermentation • In absence of O2, cell does wasteful recycling: • NADH oxidized to NAD+ (lose potential ATP) • pyruvate reduced to lactate • glycolysis can continue with new NAD+ • yeast makes ethanol, • CO2 from pyruvate • bacteria make diverse • acids, other products Fig. 19.11

  22. Oxidation not for ATP generation • Most O2 used in electron transport chain. • Some enzymes use O2 for substrate oxidation, • not for ATP generation: • Oxidases transfer e- to O2 • [Cytochrome oxidase in electron transport chain] • Peroxidases in peroxisome • Oxygenases transfer e- • and O2 to substrate • Form H2O and S-OH • Hydroxylases • (eg. Phe -> Tyr) Fig. 19.12

  23. VII Energy balance • Energy expenditure reflects oxygen consumption: • Most O2 is used • by ATPases Fig. 19.14

  24. Energy balance • Portion of food metabolized is related to energy use: • Basal metabolic rate • Thermogenesis • Physical activity • Storage of excess • “If you eat to much • and don’t exercise, • you will get fat” • (summarizes ATP-ADP cycle)