🔬Oxidative Phosphorylation

Oxidative phosphorylation is the final stage of aerobic respiration, occurring in the cristae membrane within the mitochondria. It's preceded by the link reaction and the Krebs cycle, which take place in the matrix.

Reduced Coenzymes

The products of the previous steps, reduced NAD and reduced FAD, are crucial here.

• Reduced NAD carries one proton (H+H+).

• Reduced FAD carries two protons (H+H+).

When these coenzymes release protons and electrons, they regenerate NAD and FAD, which return to the Krebs cycle.

⛓ Electron Transport Chain

The released electrons enter the electron transport chain, made of electron carrier proteins. As electrons move through the chain, they release energy. This energy is used to pump protons across the membrane via active transport, creating a high concentration of protons in the intermembrane space.

🧪 Proton Gradient and Chemiosmosis

The accumulation of protons in the intermembrane space generates a proton concentration gradient, also known as an electrochemical gradient. Due to this gradient, protons diffuse across ATP synthase back into the matrix, a process termed chemiosmosis.

This diffusion drives the production of ATP by providing the necessary energy for ATP synthase to turn, bringing ADP and a phosphate group together.

💧 Role of Oxygen

The final step involves oxygen acting as the terminal electron acceptor. Oxygen combines with protons and electrons to form water molecules (H2OH2​O).

Glucose + 6O26O2​ -> 6H2O6H2​O + 6CO26CO2​

Summary of Oxidative Phosphorylation

• Reduced coenzymes (NADH, FADH2FADH2​) release electrons and protons.

• Electrons travel through the electron transport chain, releasing energy to pump protons across the membrane.

• A proton gradient forms in the intermembrane space.

• Protons diffuse through ATP synthase (chemiosmosis), driving ATP production.

• Oxygen accepts protons and electrons to form water.

Importance of Oxidative Phosphorylation

The final stage of oxidative phosphorylation is crucial to get rid of the extra protons and electrons to prevent an increase in acidity (H+H+). Increased concentration of protons means decreased pH, and will denature ATP synthase, electron carriers, and enzymes in the link reaction and Krebs cycle.