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SURVEY OF BIOCHEMISTRY Electron Transport and Oxidative Phosphorylation. Redox Centers. Zoom in on the cristae:. The Mitochondrion. ~2000 per cell. How does electron transfer work?. NADH binds to Complex I on the matrix side of the membrane. Electron Transfer with NADH.
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NADH binds to Complex I on the matrix sideof the membrane
FMN resembles FAD without the adenine dinucleotide group
NADH transfers its e-to redox centers in Complex I
2e- go to FMN…
FMNH2 can then pass each e- to series of Fe-S clusters in a stepwise manner:
NADH transfers 2e-to FMN - a redox center in Complex I
Complex I contains Fe-S clusters as cofactors
Electrons pass from Fe-Sclusters to a “mobile”electron carrier cofactor called Coenzyme Q
Coenzyme Q initially binds to Complex I to pick up 2 e- from the Fe-S clusters in Complex I
Succinate-Coenzyme Q Oxidoreductase
Complex II is notshownElectrons pass fromFADH2 to CoQvia Complex II
4H+ ions get pumped out of the matrix by Complex I and CoQbut not Complex II
Coenzyme Q binds to Complex III on the Intermembrane space side
One e- goes to Cytochrome c
One e- goes into the Q cycle
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
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.
4 H+ ions get pumped from matrixinto the intermembrane spaceas 2 electrons are passed through Complex I
NADH FMN Fe-S CoQ
Cytochrome c oxidase
O2 + 4 H+ 2H2O
How does ATP get made?
Idea that the free energy needed to transport e- is conserved by the formation of a transmembrane proton gradient.
Proton gradient drives ATP synthesis.
F0 - water insolublew/ 8 types of subunits
F1 - water solubleperipheral membraneprotein w/ 5 types of subunits
O = open L = loose T = tight
Notice theseinhibitors of electron transport!
O2 + e- O2-•
Other harmful possibilities:
H2O2 + Fe2+ •OH + OH- + Fe3+
O2-• + H2O2 O2 + H2O + •OH
CON: Aerobic metabolism, with its high efficiency, tendsto produce free radicals of oxygen!