PCB3134 - Lecture 15 Redox, Proton Motive Force, Electron Transport

PCB3134 - Lecture 15 Redox, Proton Motive Force, Electron Transport

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Glycolysis: Glucose + 2ADP + 2Pi + 2NAD + 2Pyruvate + 2ATP + 2NADH + 2H + + 2H 2 O Pyruvate decarboxylation: Pyruvate + HS-CoA + NAD + AcetylCoA + CO 2 + NADH + H + The TCA cycle: AcetylCoA + 2H 2 O + FAD + 3NAD + + GDP + Pi 2CO 2 + FADH 2 + 3NADH + 3H + + GTP + HS-CoA Glucose + 2ADP + 2GDP + 10NAD + + 2FAD + 4Pi + 2H 2 O 2ATP + 2GTP + 10NADH + 2FADH 2 + 10H + + 6CO 2 Most of the energy from oxidation of glucose is stored in the high-energy electrons of the reduced coenzymes NADH and FADH 2 . How are they utilized to form ATP?
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Oxidative Phosphorylation
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Substrate-level phosphorylation: a process in which ATP is formed directly by transfer of a phosphate group from a substrate molecule to ATP. Oxidative phosphorylation: a process in which ATP formation is driven by energy that is released from electrons removed during substrate oxidation. Energy stored in the high-energy electrons of NADH and FADH2 are released as they are passed through the electron-transport chain. To understand this energy releasing process, we have to under the oxidation-reduction potentials.
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A + B + A + + B e Reducing agent Oxidizing agent Redox couple: A/A + B + /B Oxidized Oxidized
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Electron-transfer potential Electron affinity α -ketoglutarate Acetaldehyde H 2 Isocitrate Cysteine NADH NADPH Ethanol Lactate Malate FADH 2 Succinate Ubiquinol Cytochromes H 2 O Reducing agents O 2 Cytochromes Ubiqinone Fumarate FAD Oxaloacetate Pyruvate Acetaldehyde NADP + NAD + Cystine α -ketoglutarate H + Acetate Succinate Oxidizing agents
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Oxidation-Reduction Potentials Standard conditions: 1. Concentrations are 1M for solutes and ions; 2. 1 atm pressure for gases. Standard couple: H + -H 2 Standard redox potential: E 0
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E 0 : [H + ] is 10 -7 (pH of 7.0)
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For reaction: A (ox) + B (red) A (red) +B (ox) G 0 ’ = -nF E 0 For reaction: NADH +1/2O 2 + H + H 2 O + NAD + Standard potentials for the two couples: 1/2O 2 + 2H + + 2e H 2 O E 0 ’ = +0.82 V NAD + + 2H + +2e NADH + H + E 0 ’ = -0.32 V E 0 ’ = +0.82 – (-0.32) = 1.14 V G 0 ’ = -nF E 0 ’ = -(2)(23.063kacl/V.mol)(1.14V) =-52.6kcal/mol The actual G value will depend on relative concentrations of
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PCB3134 - Lecture 15 Redox, Proton Motive Force, Electron Transport

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