Brief Summary
This video explains the respiratory electron transport chain, a process occurring in the inner mitochondrial membrane. It details how protein complexes and electron carriers oxidize reduced coenzymes (NADH2 and FADH2), pass electrons through the chain, pump protons to create an ATP gradient, and ultimately form water. The video also covers the different types of phosphorylation and how ATP is generated through oxidative phosphorylation in the electron transport chain.
- The electron transport chain oxidizes NADH2 and FADH2 to generate ATP.
- Proton pumping creates an electrochemical gradient used by ATP synthase.
- The final electron acceptor is oxygen, which combines with electrons and protons to form water.
- Oxidative phosphorylation in the electron transport chain produces 32 ATP per glucose molecule.
Introduction to Respiratory Electron Transport Chain
The respiratory electron transport chain, located in the inner mitochondrial membrane, involves protein complexes, electron carriers, and proton pumps. These components work together to oxidize reduced coenzymes, specifically NADH2 and FADH2. This oxidation process releases electrons that are then passed through the electron transport chain.
Mechanism of Electron Transport Chain
As electrons move through the electron transport chain, they move from a high-energy state to a low-energy state, releasing energy in the process. This energy is used to pump protons from the mitochondrial matrix to the intermembrane space, creating an electrochemical gradient. ATP synthase then uses this proton gradient to produce ATP. The electrons eventually combine with oxygen, the final electron acceptor, to form water.
Components of the Electron Transport Chain
The electron transport chain is situated within the inner mitochondrial membrane, which is surrounded by the outer mitochondrial membrane. The space between these membranes is known as the intermembrane space, while the region inside the inner membrane is called the matrix. Key components of the chain include Complex I (NADH dehydrogenase), Complex II (FADH2 dehydrogenase), Complex III (cytochrome BC1 complex or cytochrome C reductase), and Complex IV (cytochrome AA3 complex or cytochrome C oxidase).
ATP Production and Reduced Coenzymes
Prior to the electron transport chain, glycolysis, pyruvic acid oxidation, and the Krebs cycle occur, yielding a total of 4 direct ATP molecules per glucose molecule. Additionally, 10 NADH2 and 2 FADH2 molecules are produced. The electron transport chain uses these reduced coenzymes to generate more ATP.
Electron Transfer and Proton Pumping
NADH2 from the cytoplasm (2 molecules) and mitochondria (8 molecules) enter the electron transport chain. NADH2 is oxidized by Complex I, releasing electrons that are passed to coenzyme Q (or ubiquinone), which becomes QH2. QH2 then transfers electrons to cytochrome B, then to cytochrome C1, and eventually to cytochrome C. This process results in protons being pumped across the inner mitochondrial membrane into the intermembrane space. Complex I pumps four protons, Complex III pumps four protons, and Complex IV pumps two protons per NADH2 molecule.
ATP Synthase and ATP Generation
The protons that have been pumped into the intermembrane space flow back into the mitochondrial matrix through ATP synthase. For every three protons that pass through ATP synthase, one ATP molecule is produced. Since 10 protons are pumped per NADH2 molecule, approximately three ATP molecules are generated per NADH2.
FADH2 and Electron Transport Chain
FADH2 enters the electron transport chain at Complex II, bypassing Complex I. As a result, fewer protons are pumped into the intermembrane space. Specifically, only six protons are pumped per FADH2 molecule, leading to the production of two ATP molecules.
Final Electron Acceptor and Water Formation
The final electron acceptor in the electron transport chain is oxygen. Two electrons, along with two protons, combine with one atom of oxygen to form one molecule of water.
ATP Yield and Oxidative Phosphorylation
The electron transport chain facilitates oxidative phosphorylation, where ATP is formed through the oxidation of NADH2 and FADH2. This process differs from substrate-level phosphorylation, where ATP is directly produced in glycolysis and the Krebs cycle. In the respiratory electron transport chain, ATP formation is specifically termed oxidative phosphorylation.
Glycerol-3-Phosphate Shuttle
NADH2 from glycolysis cannot directly enter the mitochondria. Instead, it uses the glycerol-3-phosphate shuttle. This process effectively converts the cytoplasmic NADH2 into FADH2 within the mitochondria, resulting in the production of two ATP molecules instead of three.
Total ATP Production
In total, the electron transport chain produces 32 ATP molecules per glucose molecule through oxidative phosphorylation. When combined with the 4 ATP molecules produced through substrate-level phosphorylation, the total ATP yield per glucose molecule is 36.
