SURVEY OF BIOCHEMISTRY Electron Transport and Oxidative Phosphorylation
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SURVEY OF BIOCHEMISTRYElectron Transport and
Oxidative Phosphorylation
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Redox Centers
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The Mitochondrion
Zoom in on the cristae:
~2000 per cell
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How does electron transfer work?
NADH binds to Complex I on the matrix side
of the membrane
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Electron Transfer with NADH
NADH transfers its e-
to redox centers in Complex I
2e- go to FMN…
FMN resembles FAD without the adenine dinucleotide group
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Electron Transfer with FMNH2
NADH transfers 2e-
to FMN - a redox center in Complex I
FMNH2 can then pass each e- to series of Fe-S clusters in a stepwise manner:
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Fe-S Clusters in Complex I
Complex I contains Fe-S clusters as cofactors
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Coenzyme Q (Ubiquinone)
Electrons pass from Fe-Sclusters to a “mobile”
electron carrier cofactor called Coenzyme Q
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Electron Transfer with CoQ
Coenzyme Q initially binds to Complex I to pick up 2 e- from the Fe-S clusters in Complex I
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Complex II
Succinate-Coenzyme Q Oxidoreductase
FADH2
Complex II is notshown
Electrons pass fromFADH2 to CoQvia Complex II
4H+ ions get pumped out of the matrix by
Complex I and CoQbut not Complex II
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Electron Transfer with CoQ
Coenzyme Q binds to Complex III on the
Intermembrane space side
One e- goes to Cytochrome c
One e- goes into the Q
cycle
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Electron Transfer with Cyt c
Once CoQ loses its 2e-,
it can dissociate from the
upper region of Complex
III and rebind near the
matrix sideand pick up the e- it just
donated!
Meanwhile, Cytochrome c carries its
e- to Complex IV
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Electron Transfer with Cyt c
Another CoQ carrying 2e- can bind to Complex III, passing one of its e- to Cytochrome c and one into the Q cycle and ultimately to the
original CoQ molecule.
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Proton Pumping from Matrix
NADH FMN Fe-S CoQ
4 H+ ions get pumped from matrixinto the intermembrane space
as 2 electrons are passed through Complex I
(mechanism unknown)
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Complex III and Complex IV
Cytochrome bc1
O2 + 4 H+ 2H2O
Cytochrome c oxidase
How does ATP get made?
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Chemiosmotic Theory
Idea that the free energy needed to transport e- is conserved by the formation of a transmembrane
proton gradient.
Proton gradient drives ATP synthesis.
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Complex V: ATP Synthase
F1F0 ATPase
F0 - water insolublew/ 8 types of subunits
F1 - water solubleperipheral membraneprotein w/ 5 types of
subunits
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Binding Mechanism in ATP Synthase
O = open L = loose T = tight
1. ATP binds into the T protomer first2. ADP and Pi bind to the L protomer3. Supply of energy induces a conformational change4. ATP goes to the O protomer and is released5. ATP is synthesized at the T protomer
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Overview of Electron Transport
Notice theseinhibitors of
electron transport!
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Coordinated Control of Glycolysis and the TCA Cycle
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Pros and Cons of Aerobic Metabolism
Anaerobic Metabolism of Glucose:
C6H12O6 + 2 ADP + 2 Pi 2 Lactate + 2 H+ + 2 H2O + 2 ATP
Aerobic Metabolism of Glucose:
C6H12O6 + 32 ADP + 32 Pi + 6O2 6 CO2 + 38H2O + 32 ATP
PRO: Aerobic metabolism is up to 16x more productivethan anerobic metabolism!
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Pros and Cons of Aerobic Metabolism
O2 + e- O2-•
CON: Aerobic metabolism, with its high efficiency, tendsto produce free radicals of oxygen!
Superoxideradical
Other harmful possibilities:
H2O2 + Fe2+ •OH + OH- + Fe3+
O2-• + H2O2 O2 + H2O + •OH
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Superoxide Dismutase (SOD)
• An inherent antioxidant enzyme
2O2-• + 2H+ O2 + H2O2
Catalase
SOD
2H2O2
2 H2O + O2
Otherpotential
antioxidants