Oxidative Phosphorylation

Question 0

Explain the 5 stages of oxidative phosphorylation

Answer 0

1. Reduced NAD interacts with the first protein complex in the ETC, it is dehydrogenated (oxidised) into NAD

• The H+ ions stay in the matrix, the e- are passed along the ETC in a series of redox reactions.

2. The proteins in the ETC pump H+ ions from the matrix into the intermembrane space.

• The inner membrane is impermeable to H+ ions so the protons accumulate setting up a pH, electrochemical and concentration gradient.

3. The protons flow down their gradient by chemiosmosis through the channel in ATP synthase.

• The proton motive force causes the head of ATP synthase to turn, phosphorylating ADP with Pi forming ATP.
4. The electrons from the ETC get passed to O2 (final electron acceptor).

• 4 electrons and 4H+ combine with O2 to form H2O
• 4e- + 4H+ + O2 –> 2H2O

5. Reduced FAD interacts with the second protein complex in the ETC

• It is reoxidised into FAD, 2H+ and 2e-
• The electrons are passed along the ETC in a series or redox reactions

Question 1

Where does oxidative phosphorylation take place?

Answer 1

Cristae

Question 2

Explain why the theoretical yield of ATP per glucose molecule is rarely achieved

Answer 2

32 is the theoretical yield of ATP, but this is rarely achieved because:

• Some protons leak across the mitochondrial membrane, reducing the number of protons to generate the proton motive force.
• Some ATP produced is used to actively transport Pyruvate into the mitochondria.