Lecture 32 - The electron transport chain Flashcards
Oxidative phosphorylation
Oxidative phosphorylation is the coupled process of: electron transport through the electron transport chain AND the phosphorylation of ADP to ATP by ATP-synthase
They are coupled by a proton gradient
The ETC makes the proton gradient
ATP-synthase uses the proton gradient
Proton gradient
Oxidative phosphorylation process is coupled by a proton gradient
The ETC makes the proton gradient - the inner membrane provides a barrier so that the proton gradient can be created
ATP-synthase uses the proton gradient
Where is the ETC?
The ETC is in the inner membrane of mitochondria
All processes except for glycolysis (cytoplasm) occurs in the mitochondria
Experimental evidence of the location of the ETC
Isolate mitochondria from cells via centrifuge then …
Treat with strong detergent, soubise all the membranes which results in the ETC not working
Treat with mild detergent, only removes outer membrane, ETC still works
Note - detergents disrupt membranes
Overview of the ETC
Electrons are passed through a series of carriers
Electrons from NADH and FADH2 are fed into the electron transport chain (NADH and FADH2 are oxidised)
These electrons will ultimately reduce molecule oxygen to water (oxygen is the terminal electron acceptor)
Protons are pumped as the electrons are transported through the ETC
The ETC is organised into a series of _______ between which ___________ transport ______
Complexes
Mobile carriers
Electrons
ETC organisation
ETC organised into four complexes
Each complex contains multiple carriers
Two mobile carriers - UQ (CoQ) and cytochrome C (Cyt C)
Movement of electrons through the electron transport chain involves carriers undergoing a series of redox reactions
Each carrier accepts electrons (s) (is reduced) in one redox reaction and then donates electron(s) (is oxidised) in another redox reaction
ETC is a series of redox reactions tasing on electrons to the next carrier and it is also going to regenerate the previous carrier so that the next lot of electrons can come through
What happens as the electrons move through the carriers?
Energy is released
Electrons move to carriers with a higher reduction potential (oxygen has the highest reduction potential) - for each of the redox reactions in the ETC, we are going up in reduction potential and a negative delta G and therefore are releasing energy which is used to form the proton gradient
Energy is released (the delta G is negative)
Oxygen has the highest reduction potential hence why it is the terminal electron acceptor
Energy released in the ETC is used to …
Used to translocate protons across the mitochondrial inner membrane
Intermembrance space has higher H+ concentration and therefore a lower pH
Matrix has a lower H+ concentration and therefore has a higher pH
Electron flow through the ETC
NADH - complex I - UQ - Complex III - Cyt C - Complex IV - O2
OR
FADH2 - complex II - UQ - Complex III - Cyt C - Complex IV - O2
Electron flow path with NADH
NADH - complex I - UQ - Complex III - Cyt C - Complex IV - O2
Electron flow path with FADH2
FADH2 - complex II - UQ - Complex III - Cyt C - Complex IV - O2
Inhibitors of electron flow through the ETC
Rotenone
Cyanide
Carbon monoxide
Rotenone and the ETC
Inhibits the transfer of electron from complex I to CoQ/UQ
Cyanide and the ETC
Binds to a carrier in complex IV
Carbon monoxide and the ETC
Carbon monoxide binds where oxygen binds
Problems with inhibiting the ETC…
Stop flow of electrons through the ETC
Buildup of reduced coenzymes (NADH and FADH2) - they are holding on to electrons and want to give it to something
No proton gradient formed
Reactive oxygen species produced
Complex I
NADH is oxidised at Complex I
Two electrons released into the ETC - two electrons travel as a pair through complex one
4 protons are pumped for each NADH oxidised
Complex II
FADH2 is oxidised at Complex II (use FADH2 cause it needs more power for this reaction, FAD is always associated with the enzyme and needs to be regenerated back (shared reaction with CAC))
SDH reaction is shared with the CAC
Two electrons released into the ETC
No protons are pumped
UQ/CoQ
Complex I and Complex II both pass two electrons to UQ/CoQ
UQ can move within the inner mitochondrial membrane
CoQ releases one electron at a time to complex III
CoQ undergoes two- electron redox reactions (like NADH and FADH2) - but can accept/release one electron at a time so can have a kind of intermediate
Complex III
Complex III releases one electron at a time to cytochrome C
Complex III pumps 4 protons across the inner membrane (for one coenzyme/2 electrons)
Cytochrome C
Moves on outer surface of the inner mitochondrial membrane
Cytochrome C carries one electron at a time from complex III to complex IV
Cytochrom C is a _______ containing protein
Heme
Cyt C carries one electron via reversible Fe2+/Fe3+ redox reactions
Complex IV
Complex IV accepts one electron at a time from cut c
Reduces oxygen to water (terminal electron acceptor)
For 1 NADH/FADH2 (2 electrons) - 2 H+ pumped
For 1 NADH/FADH2 (2 electrons) - 1/2 O2 + 2H+ -> H2O
Biologically the last carrier in complex IV waits until it has 4 electrons: O2 + 4H+ -> 2H2O
Energy accounting for the ETC
NADH : 4 + 4 + 2 = 10 protons pumped
FADH2: 4 + 2 = 6 protons pumped
