Overview
This lecture explains the final stage of aerobic respiration: oxidative phosphorylation and chemiosmosis, focusing on how ATP is produced in mitochondria.
Chemiosmosis and ATP Synthase
- Chemiosmosis is the main method for ATP production via the enzyme ATP synthase.
- ATP synthase is a membrane enzyme embedded in the inner mitochondrial membrane.
- ATP synthase uses energy from hydrogen ions (protons) moving down their concentration gradient to produce ATP from ADP and phosphate.
- The inner mitochondrial membrane is folded (cristae) to increase surface area for more ATP synthase enzymes.
- For ATP synthesis, the intermembrane space must have a higher proton concentration than the matrix.
Oxidative Phosphorylation and Proton Gradient Formation
- The electron transport chain (ETC) is a series of membrane proteins located next to ATP synthase in the inner mitochondrial membrane.
- ETC proteins transfer electrons from one protein to another, losing energy at each stage.
- The energy from electrons powers ETC proteins to pump protons from the matrix into the intermembrane space, creating a proton gradient.
- Protons diffuse back into the matrix through ATP synthase, powering ATP production (chemiosmosis).
Role of NADH, FADH2, and Oxygen
- Reduced NAD (NADH) and reduced FAD (FADH2) are generated in glycolysis, link reaction, and Krebs cycle.
- NADH and FADH2 are oxidized, releasing hydrogen atoms, which split into protons (H⁺) and electrons.
- Electrons travel through the ETC, while protons are pumped into the intermembrane space.
- Oxygen acts as the final electron acceptor in the ETC, combining with electrons and protons to form water.
Summary of Aerobic Respiration Steps
- Glucose is broken down into pyruvate (glycolysis), acetyl-CoA (link reaction), and fully oxidized in the Krebs cycle.
- Reduced NAD and FAD are generated and carry hydrogens to the mitochondria.
- At the inner membrane, NADH and FADH2 release hydrogen atoms; ETC uses electrons to pump protons.
- Proton gradient drives ATP synthase for ATP production; oxygen accepts electrons and protons to form water.
- Regenerated NAD and FAD return to earlier respiration steps to carry more hydrogen.
Key Terms & Definitions
- Chemiosmosis — Movement of protons down their concentration gradient through ATP synthase to make ATP.
- ATP Synthase — Membrane enzyme that synthesizes ATP using a proton gradient.
- Electron Transport Chain (ETC) — Series of proteins in the inner mitochondrial membrane transferring electrons and pumping protons.
- Proton Gradient — Difference in proton concentration across the inner mitochondrial membrane.
- Oxidative Phosphorylation — ATP production process using energy from electrons moving through the ETC.
- Final Electron Acceptor — Oxygen, which receives electrons and protons to form water.
Action Items / Next Steps
- Review the steps and locations of glycolysis, link reaction, Krebs cycle, and oxidative phosphorylation.
- Prepare to discuss what happens if oxygen is not available (for next class).