Respiratory electron transport chain

Question 1

Briefly describe the electron transport chain

Answer 1

A series of redox centres with increasing more positive redox potentials (higher affinity for electrons)
Electrons pass through complexes until it reaches a terminal acceptor

Question 2

How many complexes are involved in the electron transport chain of respiration?

Answer 2

4

Question 3

What is the structure of complex I of ETC?

Answer 3

had NAD binding site, 7Fe-S centres, FMN, tightly bound ubiquinone

Question 4

What is the role of complex I of ETC?

Answer 4

binds and oxidises NADH, uses the 2 electrons FMN to FMNH2. FMNH2 oxidised and the 2 electrons pass to the Fe-S centres the to bound ubiquinone and to final FE-S centre N2. These electrons then reduce free UQ causes transient negative charge (UQ2-) which is electrostatically transmitted to integral part of complex I via Glu and Lys residues causing horizontal movement of horizontal a-helices alternately opening up half channels on the N side and P side to allow the movement of 4H+

Question 5

What is the stoichiometry of complex I?

Answer 5

4H+/2e-

Question 6

What is the role of complex II?

Answer 6

Succinate dehydrogenase: oxidises succinate to fumarate, producing FADH2 which transfers 2 electrons to UQ in membrane

Question 7

What is the stoichiometry of complex II?

Answer 7

no H+ pumping

Question 8

What is the structure of complex III?

Answer 8

Cytochrome b - has Qn site on N side, Qp site on P side, two haem groups position on either side of membrane (bH - higher affinity on N side, bL - lower affinity on P side)
cytochrome C1 - has haem group
Rieske protein - 2Fe-2S centre

Question 9

What is the role of complex III?

Answer 9

Q-cycle

1) UQH2 binds at Qp site of cytochrome b and is oxidised - 2H+ move to P side, one electron goes to cytochrome C via 2Fe-2S Rieske centre and cytochrome C1 haem, other electron goes to bL and the n to bH, then to the UQ bound at the Qn site to semi-reduce it to UQ-
2) second UQH2 binds at Qp site of cytochrome b and is oxidised - 2H+ move to P side, one electron goes to cytochrome C via 2Fe-2S Rieske centre and cytochrome C1 haem, other electron goes to bL and the n to bH, then to the UQ- bound at the Qn site to semi-reduce it to UQH2 and released into pool.

Question 10

What is the stoichiometry of complex III?

Answer 10

4H+/2e-

Question 11

What is the final electron acceptor?

Answer 11

Water

Question 12

What is the structure of complex IV in Paracoccus?

Answer 12

4 subunits:
I = 12 TMS domains (form 3 pores for H+ pumping), haem, alpha, alpha3, CuB redox centres
II = 2 TMS domains, CuA redox centre
III = 7 TMS domains
IV = 1 TMS domain

Question 13

How many subunits does the human complex IV have?

Answer 13

13

Question 14

What is the role of complex IV in Paracoccus?

Answer 14

sequential delivery of 4 electrons from cytochrome C

1) first 2 electrons reduce CuB and the Fe of haem alpha3 = these redox centres are in close proximity and then bind oxygen to forma peroxide bridge
2) second 2 electrons allow formation of hydroxyl groups. the uptake of 2 H+ allows the release of two water molecules

Question 15

What is the stoichiometry of complex IV?

Answer 15

2H+/2e- (total of 4 H+ as 4 electrons transferred)