Cellular Respiration: ETC and Chemiosmosis Notes
Cellular Respiration: ETC and Chemiosmosis
Overview
- Majority of ATP production occurs via the electron transport chain (ETC).
- ETC takes place across the inner mitochondrial membrane.
- Involves the transfer of high-energy electrons (from NADH & FADH2) through a series of carrier proteins.
Electron Transport Chain (ETC) Steps
Electron Transfer and Energy Release:
- As electrons move down the chain, energy is released.
- This energy fuels the pumping of hydrogen ions (H^+) across the inner mitochondrial membrane.
- H^+ is moved from the matrix to the intermembrane space, establishing a concentration gradient.
Chemiosmosis and ATP Synthesis:
- The resulting concentration gradient (high H^+ in the intermembrane space, low H^+ in the matrix) drives H^+ through ATP synthase.
- ATP synthase is a membrane-embedded protein complex.
- The flow of H^+ through ATP synthase powers the conversion of ADP to ATP.
Final Electron Acceptor:
- Oxygen acts as the final electron acceptor in the ETC.
- Oxygen accepts electrons and hydrogen ions to form water (H_2O).
- The water molecule is released as a byproduct.
Role of NADH and FADH2
- NADH and FADH2 deliver electrons to the electron transport chain.
- They are produced during glycolysis and the Krebs cycle.
- After donating electrons, they are recycled to NAD+ and FAD, respectively.
- NAD+ and FAD can then be reused in glycolysis and the Krebs cycle.
Energy Release and H+ Gradient
- As electrons move from one protein to another in the ETC, a small amount of energy is released.
- Released energy is used to pump H^+ into the intermembrane space, creating a concentration gradient.
Oxygen as the Final Electron Acceptor
- Oxygen is crucial for the ETC to function.
- The reduction of oxygen to form water is represented by the equation: 2H^+ + \frac{1}{2}O2 + 2e^- \rightarrow H2O
Consequences of Oxygen Deprivation
- If oxygen is absent, the ETC backs up.
- NADH and FADH2 cannot be recycled back to NAD+ and FAD.
- This backup affects the entire process, including glycolysis.
- Lack of oxygen leads to no ATP production leading to cell death which in turn leads to organism death.
Chemiosmosis Details
- Chemiosmosis is the process responsible for producing the majority of ATP in cellular respiration i.e., ~$32 ATP per glucose molecule.
- Chemiosmosis necessitates:
- An ATP synthase channel located in the inner mitochondrial membrane.
- The buildup of H^+ in the intermembrane space due to the electron transport chain.
Mechanism of Chemiosmosis
- The inner mitochondrial membrane is generally impermeable to H^+ ions.
- The ATP synthase channel provides the only route for H^+ to diffuse back into the matrix.
- As H^+ flows down its concentration gradient through ATP synthase, energy is released.
- ATP synthase harnesses this energy to synthesize ATP.
- The yield is ~32 ATP per glucose molecule.
Summary of Aerobic Cellular Respiration
- Four main stages: glycolysis, Krebs cycle preparation, Krebs cycle, and electron transport system.
- Glycolysis
- Occurs in the cytoplasm.
- Glucose is split into two three-carbon molecules called pyruvate.
- A small amount of ATP is produced.
- Proceeds without oxygen.
- Krebs Cycle Preparation
- Occurs in the matrix of the mitochondrion.
- Pyruvate is used to make a molecule called acetyl CoA.
- Carbon dioxide is released.
- Krebs Cycle
- Processes acetyl CoA through a series of reactions that extract electrons and hydrogen ions.
- A small amount of ATP is produced.
- Electrons and hydrogen ions are carried to an electron transport system.
- Carbon dioxide is released.
- Electron Transport System
- Occurs inside the mitochondrion.
- Electrons are transferred through a series of molecules that accept and then pass on the electrons.
- A large amount of ATP is produced.
- Oxygen is the final acceptor of electrons and combines with hydrogen ions to form water.
- Glycolysis
ATP Production Numbers
- Glycolysis: 2 ATP
- Krebs Cycle: 2 ATP
- Electron Transport System: Up to 32 ATP
- Total: ~36 ATP per glucose molecule