Lecture 29 - Oxidative phosphorylation: Electron Transport Chain

Question 1

What are the two reactions coupled to produce oxidative phosphorylation?

Answer 1

Electron transport via the electron transport chain and the phosphorylation of ADP to ATP by ATP synthase

Question 2

What are the two reactions coupled by?

Answer 2

A proton gradient

Question 3

What is the electron transport chain?

Answer 3

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

Question 4

Where is the electron transport chain?

Answer 4

On the inner membrane of the mitochondria

Question 5

How do we know the ETC is in the inner membrane?

Answer 5

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

Question 6

What is the ETC organised into?

Answer 6

Four complexes labeled I to IV

Question 7

What does each complex contain?

Answer 7

Multiple carriers

Question 8

What are the two mobile carriers?

Answer 8

UQ and cyt c

Question 9

What happens to each carrier in the ETC?

Answer 9

Each carrier accepts electron(s) to be reduced in one redox reaction and then donates electron(s) to be oxidised in another redox reaction

Question 10

Where do electrons move?

Answer 10

Electrons move from lower to higher reduction potential

Question 11

What happens when electrons move to carriers with a higher reduction potential?

Answer 11

Energy is released

Question 12

What has the highest reduction potential?

Answer 12

Oxygen

Question 13

What happens to electrons as they move through the carriers?

Answer 13

As electrons move to carriers with a higher reduction potential energy is released

Question 14

Is the ETC energetically favourable to unfavourable

Answer 14

Favourable

Question 15

What is the energy released as electrons move down the ETC used for

Answer 15

To move protons across the mitochondrial membrane

Question 16

What is the path of NADH through the ETC?

Answer 16

Complex I → UQ → Complex III → Cyt c → Complex IV → O2

Question 17

What is the path of FADH2 through the ETC?

Answer 17

Complex II → UQ → Complex III → Cyt c → Complex IV → O2

Question 18

What are the three inhibitors of electron flow through the ETC?

Answer 18

Rotenone, Cyanide and carbon monoxide

Question 19

How does rotenone inhibit electron flow?

Answer 19

Inhibits electron transfer from complex I to UQ

Question 20

How does cyanide inhibit electron flow?

Answer 20

Binds to a carrier in complex IV

Question 21

How does CO (Carbon Monoxide) inhibit electron flow?

Answer 21

It binds where O2 is supposed to bind

Question 22

Overall, how does inhibition prevent ATP synthesis?

Answer 22

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

Question 23

What is the electron flow through complex I?

Answer 23

NADH is oxidised, 2 e- are released into ETC, 4 protons are pumped for each NADH oxidised

Question 24

What is the electron flow through complex II?

Answer 24

FADH2 is oxidised (SDH reaction is shared with the CAC), 2 electrons released into ETC, no protons pumped

Question 25

What is the electron flow through UQ?

Answer 25

Complex I and II both pass 2 electrons to UQ, UQ can move within the inner mitochondrial membrane

Question 26

What is the electron flow through complex III?

Answer 26

Complex III releases 1 electron at a time to cyt c and pumps 4 protons across the inner membrane (for every two electrons)

Question 27

What is the electron flow through cyt c?

Answer 27

Cyt c moves on the outer surface of the inner membrane. Carries 1 electron at a time to complex IV

Question 28

What is the electron flow through complex IV?

Answer 28

Accepts 1 electron at a time from cyt c, reduced O2 to H2O. For 1 NADH/FADH2 - 2H+ pumped and 1/2O2 + 2H+ → H2O

Question 29

What happens to H2O synthesis biologically?

Answer 29

Complex IV waits until it has all 4 e- before synthesising H2O

Question 30

What is the energy accounting from NADH?

Answer 30

4(CI) + 4(CIII) + 2(CIV) = 10 H+

Question 31

What is the energy accounting from FADH2?

Answer 31

4(CIII) + 2(CIV) = 6 H+