BIOL2171 Lecture Notes - Lecture 13: Oxidative Phosphorylation, Intermembrane Space, Succinic Acid
Oxidative Phosphorylation: Electron Transport Chain, Electron
Carriers and ATPase
Electron Transport Chain
•
o NADH go to complex 1 and gets turned into NAD+
• Its electrons go inside and undergo a number of oxidation/redox reactions
• Electrons roll downhill until they eventually meet UQ
• Each reaction gives off a bit of energy: this is an active transport mechanism to
push H+ against it concentration gradient
o UQ
• Succinate to fumarate releases FADH, and transfers electrons to UQ
• Complex 2 does not push any H+ across membrane
• After complex 2, NAD+ and FAD+ are regenerated so can be recycled in the TCA
cycle
• Swims across to complex 3 and donates all the electrons
o Complex 3
• Lots of reactions of electrons
• Iron sulphur clusters and other electron carriers are used
• Pumps another 4 H+ across membrane
• Pass electrons to Cyt c
o Like pass the parcel
o Cyt c
• Most conserved electron in biology
• Floats across to donate electrons to complex 4
• Pumps 2 H+ across membrane
• Passes electrons to oxygen
o Oxygen
• Terminal electron acceptor
• Takes electrons and makes water
• This is why you breathe in your oxygen
• Converts energy from redox reactions to a proton gradient
• Comprises integral and peripheral membrane proteins at the inner mitochondrial membrane
• Four membrane bound multiprotein complexes (I-IV)
o Complexes I, III and IV transport H+ into the intermembrane space
o NADH donates electrons to complex I
o Complex II is part of the TCA cycle and does not transport H+
o Electrons enter complex II from succinate to Fad
o Mobile, membranous "carriers" move electrons between complexes
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o Ubiquinone (UQ) moves electrons from complexes I and II to III
o Cytochrome C (cyt c) moves electrons from complex III to IV
Oxidative phosphorylation in the nutshell
• Reduction of O2 into H2O using electrons from NADH and FADH2
• Occurs on the inner mitochondrial membrane
• Explained by the chemi-osmotic theory (Peter Mitchel, 1960s)
• Involves a series of "downhill" electron transfers (exergonic)
• Energy used to drive protons through the inner membrane
• Transmembrane chemical and electrical difference of the proton gradient drives ATP synthesis
•
• Only have a proton gradient to show for the efforts of glycolysis, beta-oxidation and TCA cycle
o Debate on how this was sued to generate ATP occupied scientists for decades
o
Proton Movement Force
• The proton movement force: the movement of protons back acorss the membrane could be
utilised in ATP synthesis
• NEED:
o Proton channel
o An enzyme to synthesise ATP
o More positive on one side than the other due to H+ transport
• Proof of the proton motive force theory:
o FF-ATPase was known to be crutial in the process
o Enzyme purified and reconstituted
o Co-reconstitution with bacteriorhodopsin (BR)
o BR is a light driven proton pump
o Addition of ADP and Pi resulted in ATP synthesis
o Proton gradient required for ATP synthesis
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