Lecture 29 - Oxidative phosphorylation: Electron Transport Chain Flashcards
What are the two processes coupled to produce oxidative phosphorylation?
Electron transport via the electron transport chain and the phosphorylation of ADP to ATP by ATP synthase
What are the two reactions coupled by?
A proton gradient
What is the electron transport chain?
The process where electrons from NADH2 and FADH are passed through a series of carriers, to pump protons into the inter-membrane space of the mitochondria and create a H+ gradient
Where is the electron transport chain?
On the inner membrane of the mitochondria
How do we know the ETC is in the inner membrane?
Isolated mitochondria were treated with a strong and mild detergents to solubilise all and only the outer membranes respectively. When there are no membranes, the ETC does not work. Then there is no outer membrane, the ETC does work. Therefore the ETC is situated on the inner membrane
What is the ETC organised into?
Four complexes labeled I to IV
What does each complex contain?
Multiple carriers
What are the two mobile carriers?
UQ and cyt c
What happens to each carrier in the ETC?
Each carrier accepts electron(s) to be reduced in one redox reaction and then donates electron(s) to be oxidised in another redox reaction
Where do electrons move?
Electrons move from lower to higher reduction potential
What happens when electrons move to carriers with a higher reduction potential?
Energy is released
What has the highest reduction potential?
Oxygen
What happens to electrons as they move through the carriers?
As electrons move to carriers with a higher reduction potential energy is released
Is the ETC energetically favourable to unfavourable
Favourable
What is the energy released as electrons move down the ETC used for
To move protons across the mitochondrial membrane
What is the path of NADH through the ETC?
Complex I → UQ → Complex III → Cyt c → Complex IV → O2
What is the path of FADH2 through the ETC?
Complex II → UQ → Complex III → Cyt c → Complex IV → O2
What are the three inhibitors of electron flow through the ETC?
Rotenone, Cyanide and carbon monoxide
How does rotenone inhibit electron flow?
Inhibits electron transfer from complex I to UQ
How does cyanide inhibit electron flow?
Binds to a carrier in complex IV
How does CO2 inhibit electron flow?
It binds where O2 is supposed to bind
Overall, how does inhibition prevent ATP synthesis?
Stopped electron flow means no proton gradient can be formed and no ATP is made. Coenzymes also build up, so there is no oxidising power for other pathways
What is the electron flow through complex I?
NADH is oxidised, 2 e- are released into ETC, 4 protons are pumped for each NADH oxidised
What is the electron flow through complex II?
FADH2 is oxidised (SDH reaction is shared with the CAC), 2 electrons released into ETC, no protons pumped
What is the electron flow through UQ?
Complex I and II both pass 2 electrons to UQ, UQ can move within the inner mitochondrial membrane
What is the electron flow through complex III?
Complex III releases 1 electron at a time to cyt c and pumps 4 protons across the inner membrane
What is the electron flow through cyt c?
Cyt c moves on the outer surface of the inner membrane. Carries 1 electron at a time to complex IV
What is the electron flow through complex IV?
Accepts 1 electron at a time from cyt c, reduced O2 to H2O. For 1 NADH/FADH2 - 2H+ pumped and 1/2O2 + 2H+ → H2O
What happens to H2O synthesis biologically?
Complex IV waits until it has all 4 before synthesising H2O
What is the energy accounting from NADH?
4(CI) + 4(CIII) + 2(CIV) = 10 H+
What is the energy accounting from FADH2?
4(CIII) + 2(CIV) = 6 H+
