5.7.5: Oxidative phosphorylation and the chemiosmotic theory

Question 1

What is the final stage of aerobic respiration?

Answer 1

Oxidative phosphorylation

Question 2

What is oxidative phosphorylation?

Answer 2

The production of ATP in the presence of oxygen.

Question 3

Where does oxidative phosphorylation take place?

Answer 3

In mitochondria.

Question 4

What does oxidative phosphorylation involve?

Answer 4

It involves electron carrier proteins, arranged in chains called the electron transport chains, embedded in the inner mitochondrial membranes (the cristae), and a process called chemiosmosis.

Question 5

What is the advantage of having folds called cristae?

Answer 5

The folded cristae give a larger surface area for the electron carrier proteins and the ATP synthase enzymes.

Question 6

What are the steps of oxidative phosphorylation?

Answer 6

1. Reduced NAD and reduced FAD are reoxidised when they deliver their hydrogen atoms to the electron transport chain.
2. The hydrogen atoms released from the reduced coenzymes split into protons and electrons.
3. The protons go into solution in the mitochondrial matrix.

Question 7

How do the electrons from the hydrogen atoms pass along the chain of electron carriers?

Answer 7

• Each electron has an iron ion at its core.
• The iron gains an electron becoming reduced (Fe2+)
• The reduced iron ion can then donate an electron to the iron ion in the next electron carrier in the chain, becoming reoxidised to Fe3+.

Question 8

How are protons pumped across the inner mitochondrial membrane, into the intermembrane space?

Answer 8

As electrons pass along the chain, some of their energy is used to pump protons across the inner mitochondrial membrane, into the intermembrane space.

Question 9

As protons accumulate in the intermembrane space, what forms?

Answer 9

A proton gradient.

Question 10

What does the proton gradient generate?

Answer 10

A chemiosmotic potential that is also known as a protonmotive force. They are a source of potential energy. ATP is made using the energy of the pmf.

Question 11

Why can protons not easily diffuse through the lipid bilayer of the mitochondrial membranes?

Answer 11

The outer layer has a low degree of permeability to protons and the inner membrane is impermeable to protons.

Question 12

How can protons pass through the inner membrane and how does this form ATP?

Answer 12

• Protons diffuse through the protein channels associated with ATP synthase enzymes that are in the inner membrane.
• As protons diffuse down their concentration gradient through these channels, the flow of protons causes a conformational (shape) change in the ATP synthase enzymes that allows ADP and Pi to combine, forming ATP.

Question 13

What is chemiosmosis?

Answer 13

The flow of protons. It is coupled with the formation of ATP

Question 14

What is the role of oxygen in oxidative phosphorylation?

Answer 14

• Oxygen is the final electron acceptor.
• It combines with electrons coming off the electron transport chain and with protons, diffusing down the ATP synthase channel, forming water.
• 4H+ + 4e- + O2 —> 2H2O

Question 15

What do the coenzymes provide to the electron transport chain?

Answer 15

Protons and electrons

Question 16

Why is the theoretical yield of ATP rarely achieved?

Answer 16

• Some ATP is used to actively transport pyruvate into the mitochondria.
• Some ATP is used in a shuttle system that transports reduced NAD made during glycolysis into the mitochondria.
• Some protons may leak out through the outer mitochondrial membrane.