Electron Transport: Complex III

Question 1

What is another name for Complex III?

Answer 1

Cytochromebc1

Question 2

What does Complex III do?

Answer 2

Passes electrons from reduced CoQ to cytochrome C

Question 3

Which complex contains two b-type cytochromes, one cytochrome c, and one [2Fe-2S] cluster?

Answer 3

Complex III

Question 4

How many electrons are carried by CoQH2?

Answer 4

2 electrons

Question 5

What does Complex III allow CoQH2 to do to two cytochrome c’s?

Answer 5

Reduce them

Question 6

How many electrons does cytochrome c carry?

Answer 6

1 electron

Question 7

How many cytochrome c’s can one CoQH2 reduce?

Answer 7

2

Question 8

What is the Q Cycle?

Answer 8

Comlex III splits electron flow to both cytochrome c and cytochrome b (creating a cyclic flow to cytochrome b). This permits Complex III to pump protons from the matrix into the intermembrane space.

Question 9

How does the proton transport of the Q cycle in Complex III differ from the proton pumping mechanism of Complex I?

Answer 9

In the Q Cycle, CoQ (a redox center itself) is the proton carrier; in Complex I, proton pumping gets protons across (presumably).

Question 10

What reaction does Complex III catalyze?

Answer 10

Oxidation of CoQ by cytrochrome c

Question 11

Is the overall reaction catalyzed by Complex III exergonic or endergonic?

Answer 11

exergonic

Question 12

What is the path of electrons in Complex III?

Answer 12

CoQ to cytochrome c1 (and cytochrome b1 cycle) to cytochrome c

Question 13

From where does cytochrome c get its electrons?

Answer 13

Cytochrome c1

Question 14

What does cytochrome c do? What is its location?

Answer 14

It shuttles electrons between Complexes III and IV on the outer surface of the inner mitochondrial membrane (it is a peripheral membrane protein).

Question 15

What are the inhibitors of Complex III?

Answer 15

Antimycin A