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Overview of the respiratory chain © Michael Palmer 2014
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Functional stages in the respiratory chain 1.H 2 is abstracted from NADH+H + and from FADH 2 2.The electrons obtained with the hydrogen are passed down a cascade of carrier molecules located in complexes I–IV, then transferred to O 2 3.Powered by electron transport, complexes I, III, and IV expel protons across the inner mitochondrial membrane 4.The expelled protons reenter the mitochondrion through ATP synthase, driving ATP synthesis
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Uncoupling proteins dissipate the proton gradient © Michael Palmer 2014
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The uncoupling action of dinitrophenol © Michael Palmer 2014
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The Racker experiment: bacteriorhodopsin can drive ATP synthase © Michael Palmer 2014
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Molecules in the electron transport chain © Michael Palmer 2014
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Iron-containing redox cofactors © Michael Palmer 2014
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Flavin-containing redox cofactors © Michael Palmer 2014
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The respiratory chain produces reactive oxygen species as byproducts © Michael Palmer 2014
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Redox reactions can be compartmentalized to produce a measurable voltage © Michael Palmer 2014
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The redox potential (ΔE) is proportional to the free energy (ΔG) © Michael Palmer 2014
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Redox potentials and free energies in the respiratory chain © Michael Palmer 2014
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The first two redox steps in complex I © Michael Palmer 2014
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The reduction of coenzyme Q involves protons and electrons © Michael Palmer 2014
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The Q cycle (criminally simplified) © Michael Palmer 2014
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Reduction of oxygen by cytochrome C oxidase (complex IV) © Michael Palmer 2014
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How is electron transport linked to proton pumping? ● Some redox steps in the ETC are coupled to proton binding and dissociation, which may occur at opposite sides of the membrane. Example: Coenzyme Q cycle at complex III ● Redox steps that do not involve hydrogen directly need a different mechanism in order to contribute to proton pumping. Example: Sequence of iron-sulfur clusters and hemes in complex IV
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Linking electron movement to proton pumping: A conceptual model © Michael Palmer 2014
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Proton pumping creates both a concentration gradient and a membrane potential © Michael Palmer 2014
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Structure of ATP synthase © Michael Palmer 2014
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The binding-change model of ATP synthase catalysis © Michael Palmer 2014
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How does proton flux drive ATP synthase? © Michael Palmer 2014
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Proton flux causes c chains to rotate within the F 0 disk © Michael Palmer 2014
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A hypothetical malate-oxaloacetate shuttle © Michael Palmer 2014
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The malate-aspartate shuttle © Michael Palmer 2014
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The glycerophosphate shuttle © Michael Palmer 2014
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The two mitochondrial isocitrate dehydrogenases © Michael Palmer 2014
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Nicotinamide nucleotide transhydrogenase couples hydrogen transfer with proton transport © Michael Palmer 2014
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At rest, transhydrogenase and the isocitrate dehydrogenases form a futile cycle © Michael Palmer 2014
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When ATP demand is high, transhydrogenase turns into an auxiliary proton pump © Michael Palmer 2014
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Theoretical ATP per molecule of glucose completely oxidized © Michael Palmer 2014
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Processes other than ATP synthesis that are powered by the proton gradient ● Nicotinamide nucleotide transhydrogenase ● Uncoupling proteins; proton leak ● Secondary active transport: ○ ATP 4− /ADP 3− antiport ○ phosphate/H + symport ○ amino acid/H + symport ○ pyruvate/H + symport
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