Overview
This lecture explains the electron transport chain (ETC), its role in cellular respiration, and how ATP is produced through oxidative phosphorylation using electron carriers NADH and FADH₂.
Recap of Cellular Respiration Steps
- Glycolysis and the Krebs cycle generate a net gain of 2 ATP each and electron carriers (NADH and FADH₂).
- Most energy from glucose is stored in NADH and FADH₂, not as ATP at this stage.
Electron Transport Chain (ETC) Basics
- The ETC is located in the inner mitochondrial membrane (in bacteria, the cell membrane).
- NADH and FADH₂ donate electrons to the ETC, becoming NAD⁺ and FAD again.
- NADH leads to the production of about 3 ATP; FADH₂ leads to about 2 ATP.
Role of Protons (H⁺/Protons)
- Hydrogen ions (H⁺) and protons are the same because hydrogen ’s only component is a proton.
- Electrons moving through the ETC release energy, which is used to pump protons across the membrane, creating a gradient.
Formation of Electrochemical Gradient
- Protons are pumped outside the inner mitochondrial membrane, creating a high concentration.
- The resulting gradients are driven by charge (electrochemical) and concentration differences.
- Protons naturally want to diffuse back into the mitochondrial matrix due to these gradients.
ATP Synthase and Chemiosmosis
- Protons flow back into the mitochondrial matrix through ATP synthase, a protein complex that acts as a turbine.
- The spinning of ATP synthase enables ADP to combine with a phosphate to form ATP.
- This process of ATP generation via proton flow is called chemiosmosis.
Oxygen’s Role
- Oxygen acts as the final electron acceptor at the end of the ETC, combining with electrons and protons to form water.
- Without oxygen, the ETC halts, and ATP production stops.
Clinical Relevance
- Cyanide poisoning blocks cytochrome c in the ETC, rapidly stopping ATP production and causing death.
Key Terms & Definitions
- Electron Transport Chain (ETC) — Stepwise transfer of electrons through protein complexes to generate ATP.
- NADH/FADH₂ — Electron carriers loaded with electrons and hydrogen ions.
- Proton (H⁺) — A hydrogen ion; a hydrogen atom that has lost its electron.
- ATP Synthase — Enzyme and protein complex that synthesizes ATP as protons flow through it.
- Chemiosmosis — The movement of protons across a membrane, driving ATP synthesis.
- Oxidative Phosphorylation — ATP production using energy from electrons transferred to oxygen.
- Final Electron Acceptor — In humans, this is oxygen, forming water.
Action Items / Next Steps
- Review lecture material and diagrams relating to the electron transport chain.
- Re-watch the lecture video for better understanding.
- Ensure familiarity with terms and steps of cellular respiration.