Metabolism - Lecture Thirty-Two

Question 1

Oxidative phosphorylation is a couple process of

Answer 1

Electron transport through the electron transport chain (ETC) and the phosphorylation of ADP to ATP by ATP-synthase

Question 2

How is oxidative phosphorylation coupled?

Answer 2

By a proton gradient - The ETC makes the proton gradient and ATP-synthase uses the proton gradient

Question 3

Where is the electron chain transport?

Answer 3

In the inner membrane of the mitochondria

Question 4

Treating mitochondria with strong detergent

Answer 4

Solubilises all membrane, therefore electron transport chain doesn’t work

Question 5

Treating mitochondria with mild detergent

Answer 5

Only removes outer membrane, therefore electron transport chain still works

Question 6

The electron transport chain is organised into a series of complexes, between which mobile carriers transport electrons

Answer 6

Four complexes I to IV

Two mobile carriers: UQ (CoQ) and cyt c

Question 7

Movement of electrons through the electron transport chain involves carriers undergoing a series of redox reactions

Answer 7

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

Question 8

As electrons move through the carriers, energy is released

Answer 8

Electrons move to carriers with a higher reduction potential

Question 9

What is the energy released in the electron transport chain used for?

Answer 9

To translocate protons across the mitochondrial inner membrane

Question 10

Inhibitors of electron flow through the electron transport chain

Answer 10

Rotenone

Cyanide

Question 11

Rotenone

Answer 11

Inhibits the transfer of electrons from Complex I to Co-Q

Question 12

Cyanide

Answer 12

Binds to inter-membrane space cytochrome a3 in Complex IV

Question 13

What happens when the electron flow in the electron transport chain is inhibited?

Answer 13

Stop flow of electrons through the ETC
Build-up of reduced co-enzymes (NADH and FADH2) No proton gradient formed
Reactive oxygen species produced

Question 14

Complex I

Answer 14

NADH is oxidised
Two electrons released into the electron transport chain
4 protons are pumped for each NADH oxidised

Question 15

Complex II

Answer 15

FADH2 is oxidised
Two electrons released into the electron transport chain
No protons are pumped
SDH reaction is shared with the citric acid cycle

Question 16

CoQ

Answer 16

Complex I and II both pass two electrons to CoQ, CoQ releases one electron at a time to Complex III

Question 17

The mobile carrier CoQ

Answer 17

Undergoes two-electron redox reactions but can accept/release one electron at a time

Question 18

Complex III

Answer 18

Releases one electron at a time to Cytochrome c

Pumps 4 protons across the inner membrane (for one coenzyme/ 2 electrons)

Question 19

Cytochrome c

Answer 19

Is a heme containing protein that moves on outer surface of the inner mitochondrial membrane, it carries one electron at a time from Complex III to Complex IV via Fe2+/Fe3+ redox reactions

Question 20

Complex IV

Answer 20

Accepts one electron at a time from Cytochrome c

Reduces oxygen to water (terminal electron acceptor)

Question 21

For 1 NADH/ FADH2 (2 electrons)

Answer 21

2 H+ pumped

Question 22

For 1 NADH/ FADH2 (2 electrons)

Answer 22

1⁄2 O2 + 2H+ → H2O BUT Biologically the last carrier in Complex IV waits until it has 4 electrons: O2 + 4H+ → 2H2O

Question 23

Terminal electron acceptor

Answer 23

The last thing to accept oxygen

Question 24

NADH energy accounting

Answer 24

10 protons pumped

Question 25

FADH2

Answer 25

6 protons pumped