ETC

Question 1

Complex I: NADH dehydrogenase

Answer 1

Accepts electrons from NADH
Electrons passed through redox centres and then transferred to co-enzyme Q (ubiquinone/UQ) which is reduced to ubiquinol (picks up 2H+)
Ubiquinone is membrane soluble and carries electrons to complex III
Electron movement is used to drive transfer of 2H+ across the membrane

Question 2

Complex II: succinate dehydrogenase

Answer 2

Part of the TCA cycle
Electrons passed through redox centres and then transferred to co-enzyme Q (ubiquinone/UQ) which is reduced to ubiquinol (picks up 2H+)
Ubiquinone is membrane soluble and carries electrons to complex III
Does NOT pump H+ ions across the membrane

Question 3

Complex III: the Q cycle

Answer 3

Accepts electrons from ubiquinol
Protons from ubiquinol are released into the intermembrane space (contributes to gradient)

1st half of Q cycle:
One electron is transferred to a bound ubiquinone (semiquinone radical ion)
One electron is transferred to cytochrome c

2nd half of Q cycle:
One electron is transferred to semiquinone to form ubiquinol (recycle electrons) and 2H+ picked up from matrix
One electron is transferred to cytochrome c

Question 4

Complex IV: Cytochrome c oxidase

Answer 4

Accepts electrons from cytochrome c
Electrons are transferred via heme centre and copper atoms to oxygen
Electron transfer drives the transfer of protons into the intermembrane space

Question 5

The electron transport chain

Answer 5

NADH and FADH2 which were reduced in the TCA cycle, pass electrons to the complexes of the ETC
Oxygen serves as the final electron acceptor
Movement of electrons releases energy that is used to transfer electrons from the matrix to the intermembrane space
The proton gradient is then used to power ATP synthesis by ATP synthase