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Section 4. Fuel oxidation, generation of ATP
Fig.iv.1
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
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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
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Respiration occurs in mitochondria
Fig. iv.3
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
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Glucose is universal fuel for every cell
Fig. iv.4
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
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Chapt. 19 Cellular bioenergetics of ATP, O2
Ch. 19 Cellular bioenergeticsStudent 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
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Fuel oxidation makes ATP
Fig. 19.1
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
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ATP
High energy phosphate bond of ATP:
• Strained phosphoanhydride bond• G0’ -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
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Thermodynamics brief
Thermodynamics states what is possible:
G = change in Gibbs free energy of reaction: G = G0 + RT ln [P]/[S] (R = gas const; T = temp oK)
GG at standard conditions of1 M substrate & product and proceeding to equilibrium)
G0’ = G0 under 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, G = 0, therefore
G0’ = -RT lnKeq’ = -RT ln[P]/[S]
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Thermodynamics brief
Thermodynamics states what is possible:
• Exergonic reactions give off energy (G0’ < 0)• typically catabolic
• Endergonic reactions require energy (G0’ > 0)• typically anabolic
• Unfavorable reactions are coupled to favorable
reactions • Hydrolysis of ATP is very favorable• Additive G0’ values determine overall direction
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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
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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
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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
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III. ATP powers biochemical work
ATP powers biochemical work, synthesis:
Anabolic paths require energy: Go’ 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/molSum: 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
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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
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G depends on substrate, product concentrations
G depends on substrate, product concentrationsG = G0 + RT ln [P]/[S]
• Cells do not have 1M concentrations• High substrate can drive reactions with positive G0’• Low product (removal) can drive reactions with positive G0’
• Ex., even though equilibrium (G0’= +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 G = -0.41 favorable
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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
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V. Energy from fuel oxidation
Fig. 19.8
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+
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Oxidation/reduction
Fig. 19.9 NADH
Fig. 19.10FAD(2H)
Oxidation: reduction reactions:• Electron donor gets oxidized; recipient is reduced• LEO GER:
•Loss Electrons = oxidation; gain electrons is reduction• use coenzyme e- carriers
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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
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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
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Anaerobic glycolysis” = fermentation
‘Anaerobic glycolysis’ = fermentationIn 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
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Oxidation not for ATP generation
Fig. 19.12
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)
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VII Energy balance
Fig. 19.14
Energy expenditure reflects oxygen consumption:
• Most O2 is used
by ATPases
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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)