Oxidative Phosphorylation

• Describe the process of oxidative phosphorylation, with reference to the roles of electron carriers, oxygen and the mitochondrial cristae;

• Explain that oxygen is the final electron acceptor in aerobic respiration;

Oxidative Phosphorylation happens via the electron transport chain

• All the products from the previous stages are used in this final stage. Its purpose is to transfer the energy from molecules made in glycolysis, the link reaction and the Kreb’s cycle to ADP. This forms ATP, which can then deliver the energy to parts of the cell that need it. The synthesis of ATP as a result of the energy released by the electron transport chain is called oxidative phosphorylation

• The electron transport chain is where most of the ATP from respiration is produced. In the whole process of aerobic respiration, 32 ATP molecules are produced from one molecule of glucose: 2 ATP in glycolysis, 2 ATP in the Krebs cycle and 28 ATP in the electron transport chain

• The electron transport chain also reoxidises NAD and FAD so they can be reused in previous steps

Respiration: The 4 Parts

Respiration consists of 4 parts:• Glycolysis• Link Reaction• Krebs Cycle• Oxidative Phosphorylation (the electron

transport chain)

Oxidative Phosphorylation produces lots of ATP

• The energy needed for ATP synthesis is provided by the electron transport chain. It uses the reduced NAD and FAD from the previous 3 stages to produce 28 molecules of ATP for every molecule of glucose

What’s going on?

• It involves electron carriers embedded in the inner mitochondrial membranes

• They are folded into cristae which increases the surface area (providing more electron carriers)

• The electrons are passed along a chain of electron carriers and then donated to oxygen the final hydrogen acceptor

What’s the point?• As electrons flow along the electron transport

chain, energy is released and used by coenzymes associated with proteins 1, 3 and 4 to pump protons across the intermembrane space

• This builds up a proton gradient which is also a pH gradient (lowers the pH) and an electrochemical gradient

• The hydrogens can only get back through the ion channel which is associated with ATP synthase

• The flow of hydrogen ions through this ion channel is called chemiosmosis

Carrier 2 Carrier 3 Carrier 4

H+H+

H+H+ H+

H+

H+

H+

H+H+NADH + H+

NAD+

2H

2e-

2H+

2e-

2H2O

O2 + 2H+

ADP + Pi

ATP

ATPsynthaseStalked particle

Matrix of mitochondrion

Intermembrane space

Inner membrane of mitochondrion

Outer membrane of mitochondrion

Carrier 1

H+

Oxidative Phosphorylation produces lots of ATP

1. Hydrogen atoms are released from NADH + H+ and FADH2 (as they are oxidised to NAD+ and FAD). The H atoms split to produce protons (H+) and electrons (e-) for the chain.

The electrons move along the electron chain (made up of three electron carriers) losing energy at each level. This energy is used to pump the protons (H+) into the space between the inner and outer mitochondrial membranes (the intermembrane space)

Oxidative Phosphorylation produces lots of ATP

• The concentration of protons is higher in the intermembrane space than in the mitochondrial matrix, so an electrochemical gradient exists.

• The protons then move back through the inner membrane down the electrochemical gradient, through specific channels on the stalked particles of the cristae- this drives the enzyme ATP synthase. By spinning like a motor, this enzyme supplies electrical potential energy to make ATP from ADP and inorganic phosphate

• The protons and electrons recombine to form hydrogen, and this combines with molecular oxygen (from the blood) at the end of the transport chain to form water. Oxygen is said to be the final electron acceptor

The Importance of Oxygen

• We have learned that oxygen is the final hydrogen acceptor in respiration

• We are now gong to look at the uptake of oxygen by respiring organisms

Plenary

• Complete the missing word sheet