뒤로Cellular Respiration: Oxidative Phosphorylation & Chemiosmosis
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Cellular Respiration: Oxidative Phosphorylation & Chemiosmosis
Introduction to Oxidative Phosphorylation
Oxidative phosphorylation is the final stage of cellular respiration, occurring in the mitochondria. It utilizes the high-energy electron carriers NADH and FADH2 produced during earlier stages of respiration to generate ATP, the cell's main energy currency.
Goal: To break down NADH and FADH2, transferring their electrons through the electron transport chain (ETC) and pumping protons (H+) into the intermembrane space.
Location: The inner mitochondrial membrane.
Ultimate Electron Acceptor: Oxygen gas (O2) receives electrons at the end of the ETC, forming water.
Electron Transport Chain (ETC)
The electron transport chain is a series of protein complexes embedded in the inner mitochondrial membrane. Electrons from NADH and FADH2 are passed through these complexes, releasing energy used to pump protons across the membrane.
Main Complexes: Complex I, Complex II, Complex III, Complex IV
Process:
NADH donates electrons to Complex I; FADH2 donates to Complex II.
Electrons move through the chain, losing energy at each step.
Energy released is used to pump H+ from the mitochondrial matrix to the intermembrane space, creating a proton gradient.
Electrons finally combine with O2 and H+ to form water.
Gradient Formation: The movement of H+ ions creates an electrochemical gradient (proton motive force).
ETC Complexes Table
Complex | Electron Donor | Electron Acceptor | Proton Pumping |
|---|---|---|---|
Complex I | NADH | Ubiquinone (Q) | Yes |
Complex II | FADH2 | Ubiquinone (Q) | No |
Complex III | Ubiquinol (QH2) | Cytochrome c | Yes |
Complex IV | Cytochrome c | O2 | Yes |
ATP Synthase and Chemiosmosis
Chemiosmosis is the process by which the energy stored in the proton gradient is used to synthesize ATP. ATP synthase is the enzyme that facilitates this process.
Mechanism:
H+ ions flow back into the mitochondrial matrix through ATP synthase.
The movement of protons drives the rotation of ATP synthase, catalyzing the formation of ATP from ADP and inorganic phosphate (Pi).
Equation:
Yield: Ideally, oxidative phosphorylation produces about 32 ATP molecules per glucose.
Energy Yield in Cellular Respiration
The efficiency of cellular respiration can be measured by comparing the energy stored in glucose to the energy captured in ATP.
Glucose energy: 686 kcal/mol
ATP energy: 7.5 kcal/mol
Total ATP produced: 36 ATP (theoretical maximum)
Total ATP energy: kcal/mol
Efficiency: of glucose energy is captured in ATP during aerobic respiration.
Comparison: ETC in Mitochondria vs. Chloroplasts
Both mitochondria and chloroplasts use electron transport chains to create a proton gradient and synthesize ATP, but the sources of electrons and the final electron acceptors differ.
Mitochondria: Electrons from NADH/FADH2, final acceptor is O2.
Chloroplasts: Electrons from water, final acceptor is NADP+.
Key Terms
Oxidative phosphorylation: The production of ATP using energy derived from the redox reactions of the electron transport chain.
Chemiosmosis: The movement of ions across a semipermeable membrane, down their electrochemical gradient.
ATP synthase: An enzyme that synthesizes ATP from ADP and Pi using the energy from the proton gradient.
Electron transport chain (ETC): A series of protein complexes that transfer electrons and pump protons to create a gradient.
Example: The Follow the Electron Game
Tracking the path of electrons from NADH and FADH2 through the ETC to oxygen helps understand how energy is transformed and utilized in cells.
Application: Understanding the ETC is crucial for grasping how cells efficiently produce ATP and how disruptions can lead to metabolic diseases.
Additional info: Some details, such as the specific number of ATP produced and the comparison to chloroplasts, were expanded for academic completeness.
