Chm 635-9

Chm 635-9 - The Four Electron-Transport Complexes are...

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1 The Four Electron-Transport Complexes are Independent Complex IV • Cytochrome c oxidase • Catalyzes a four-electron reduction of molecular oxygen (O 2 ) to water (H 2 O) • Source of electrons is cytochrome c (links Complexes III and IV) • Cytochrome c oxidase utilizes 2 hemes ( a and a 3 ) and 2 copper sites Translocates 2H + into the intermembrane space • Iron atoms (hemes of cyt a ) and copper atoms are both reduced and oxidized as electrons flow
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2 http://www.nature.com/nrg/journal/v2/n5/animation/nrg0501_342a_swf_MEDIA1. html Electron transfer and proton flow in Complex IV Cytochrome c oxidase - Combination of cytochromes • A complex of 10 protein subunits that contains 2 cytochromes (a and a3) and proteins with copper centers that provide multiple centers for oxidation-reduction • Consists of, 2 types of prosthetic groups - 2 heme and 2 Cu. • Fe 3+ Fe 2+ • Cu 2+ Cu 1+ • Source of electrons is cytochrome c (links Complexes III and IV) • Catalyzes a four-electron reduction of O 2 to water (H 2 O) • Translocates H + into the intermembrane space and contributes to the proton gradient
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3 Complex IV Transfers Electrons from Cytochrome c to Reduce Oxygen on the Matrix Side NADH is oxidized by Complex I Complex I is reduced Complex I is oxidized by Ubiquinone Ubiquinone is reduced Succinate is oxidized by Complex II Complex II is reduced Complex II is oxidized by Ubiquinone Ubiquinone is reduced Ubiquinone is free to diffuse through the mitochondrial inner membrane Ubiquinone is oxidized by Complex III Complex III is reduced Complex III is oxidized by Cytochrome C Cytochrome C is reduced Cytochrome C is free to diffuse through the mitochondrial inter-membrane space Cytochrome C is oxidized by Complex IV Complex IV is reduced Complex IV is oxidized by oxygen Oxygen is reduced Electron transport chain
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4 Electron Transfer Energy Stored in a Proton Gradient: The Mitchell Hypothesis The proton and electrochemical gradients existing across the inner mitochondrial membrane.
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5 Calculation of the P:O ratio #H + translocated/2e - 44 2 Since 4 H + are required for each ATP synthesized: Complex I III IV For NADH : 10 H + translocated / O (2e - ) P/O = (10 H + / 4 H + ) = 2.5 ATP/O For succinate substrate = 6 H + / O (2e - ) P/O = (6 H + / 4 H + ) = 1.5 ATP/O ATP-ADP Translocase Mediates the Movement of ATP & ADP Across the Mitochondrial Membrane
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6 Adenine Nucleotide and Phosphate Translocases Active Transport of ATP, ADP and P i Across the Mitochondrial Membrane • ATP is synthesized in the mitochondrial matrix • ATP must be transported to the cytosol, and ADP and P i must enter the matrix • ADP/ATP carrier exchanges mitochondrial ATP 4- for cytosolic ADP 3- • The exchange causes a net loss of -1 in the matrix (draws some energy from the H + gradient)
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Chm 635-9 - The Four Electron-Transport Complexes are...

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