Lecture 32: ELECTRON TRANSPORT CHAIN Flashcards
What is oxidative phosphorylation?
The coupled process of electron transport through the electron transport chain (ETC) and the phosphorylation of ADP to ATP by ATP synthase
What are the ETC and ATP synthesis coupled by?
A proton gradient
What makes the proton gradient?
The ETC
What uses the proton gradient?
ATP synthase
Where does the ETC occur?
In the inner mitochondrial membrane
What does the inner mitochondrial membrane provide?
A barrier to form the proton gradient
Where are reduced coenzymes found?
Mainly in the matrix
What must be used to extract mitochondria from cells?
Tissue high in mitochondria such as liver
What is first done with the tissue?
Homogenisation in buffered solution to get homogenate
What is done with homogenate?
Centrifuge at 1000 xg to get debris and nuclei (heavy at bottom) and supernatant
What is done with the supernatant?
Centrifuge at 7000xg to get a pellet of mitochondria at the bottom and a supernatant of membranes, ribosomes and cytoplasm on top
What happens when extracted mitochondria are treated with strong detergent?
All membranes are solubilised and the ETC doesn’t work
What happens when extracted mitochondria are treated with mild detergent?
Only the outer membrane is removed and the ETC still works
What happens in the ETC?
Electrons are passed through a series of carriers
Where are the electrons in the ETC from?
NADH and FADH2 (they are oxidised)
What do the electrons do in the ETC?
Reduce oxygen to water
What is the terminal electron acceptor of the ETC?
Oxygen
What happens as electrons are transported through the ETC?
Protons are pumped
How many complexes are in the ETC?
Four (I to IV)
What does each complex contain?
Multiple carriers (carriers are organised into complexes)
How many mobile carriers in the ETC?
Two
What are the two mobile carriers?
Ubiquinone (UQ)/CoenzymeQ (CoQ) and cytochrome C (CytC)
What does movement of electrons involve?
Carriers undergoing a series fo redox reactions
what does each carrier do?
Accept electron(s) (is reduced) in one redox reaction and then donates electron(s) (is oxidised) in another redox reaction
Where do electrons move?
To carriers with a higher reduction potential (oxygen has the highest reduction potential)
What happens as electrons move between carriers?
Energy is releases (delta g is negative)
What is the energy released used for?
To translocate protons across the inner mitochondrial membrane to the intermembrane space
What is the path that electrons from NADH take?
Complex 1 > UQ > Complex 3 > Cyt c > Complex 4 > Oxygen
What is the path that electrons from FADH2 take?
Complex 2 > UQ > Complex 3 > Cyt c > Complex 4 > Oxygen
What happens at complex 1?
NADH is oxidised and two electrons are released into the ETC
How many protons are pumped at Complex 1?
Four protons for each NADH oxidised
What happens at complex 2?
FADH2 is oxidised and two electrons are released into the ETC
What reaction happens at Complex 2?
The SDH reaction which is shared with the citric acid cycle
How many protons are pumped at complex 2?
None
What do complex 1 and 2 both do?
Pass two electrons to UQ/CoQ
What can UQ do?
Move within the inner mitochondrial membrane
What is UQ?
A coenzyme (not from a vitamin) which can exist in reduced and oxidised forms
What does Co-Q undergo?
Tow-electron redox reactions (like NADH and FHAD2) but can accept or release one electron at a time
Where does Co-Q release electrons?
One at a time to Complex 3 by the Q-cycle
What does Complex 3 do?
Release one electron at a time to cytochrome c
How many protons are pumped at complex 3?
Four (1 coenzyme=2 electrons)
Where does cytochrome c move?
On the outer surface of the inner mitochondrial membrane
What does cytochrome c do?
Carry one electron at a time from complex 3 to complex 4
What is cytochrome c?
A haem containing protein
How does chytochrome c carry its electron?
Via reversible Fe2+/Fe3+ redox reactions
What does Complex 4 do?
Accepts one electron at a time from cytochrome c and reduces oxygen to water
How many protons pumped at complex 4 per 1 NADH/FADH2?
2
What is the reaction per 1 NADH/FADH2 at complex 4?
1/2O2 + 2H+»_space;> H20
What is the biological reaction at complex 4?
it waits until it has four electrons (oxidation of two coenzymes): O2 + 4H+»_space; 2H2O
What are some inhibitors of electron movement through the ETC?
Rotenone, cyanide and carbon monoxide
What does rotenone do?
Inhibits electron transfer from complex 1 to Co-Q
What does cyanide do?
Binds to a carrier in complex 4
What does carbon monoxide do?
Binds where oxygen binds
What is the effect if inhibiting electron movement?
Stops the flow of electrons through the ETC, no proton gradient is formed (ATP not made), build up of reduced coenzymes (NADH and FADH2) so no oxidising power for other pathways and reactive oxygen species which are damaging are produce
How may protons pumped per NADH?
4+4+2=10
How many protons pumped per FADH2?
4+2=6
