4.5: Electron transport chain and oxidative phosphorylation

Question 1

Where is the electron transport chain (ETC) located?

Answer 1

Made up of 4 protein complexes (I-IV) which are embedded in the inner mitochondrial membrane.

Question 2

List all the components of ETC

Answer 2

• Protein complexes I, II, III, IV
• Coenzyme Q (CoQ)
• Cytochrome c
• Oxygen (Final electron acceptor)

Question 3

Where is e- from NADH and FADH2 donated to in the ETC?

Answer 3

e- from electron carriers are harvested at either complex I or II.

Question 4

What happens to e- during ETC?

Answer 4

Once donated to complex I/II, e- are transported to complex III and then through complex IV, passing from electron donors -> acceptors.

Question 5

What is the final electron acceptor

Answer 5

Oxygen molecule. Accepts e- and reduced to form water, a reaction catalyzed by complex IV.

Question 6

How do e- travel from one protein complex to another?

Answer 6

Thanks to Coenzyme Q (CoQ) and Cytochrome c.

2 e- in complex I/II -> CoQ -> CoQH2 -> Complex III -> Cytochrome c -> Complex IV

Question 7

How is a proton gradient created?

Answer 7

During ETC, complexes I, III, and IV use some energy to pump protons across the inner mitochondrial membrane.
Furthermore, the inner mitochondrial membrane is selectively permeable.

Question 8

How does a proton gradient store energy?

Answer 8

Protons in the intermembrane space want to diffuse back to the mitochondrial matrix (difference in concentration and charge). Inner mitochondrial membrane blocks this movement and the result is potential energy.

Question 9

How is potential energy converted into chemical energy of ATP?

Answer 9

The proton gradient needs to be released, and this has to be coupled with the synthesis of ATP.
ATP synthase enables this coupled reaction.

Question 10

What are the main subunits of ATP synthase?

Answer 10

Fo: Forms the channel in the inner mitochondrial membrane for protons to flow through.
F1: Catalytic unit that synthesizes ATP.