Cellular Respiration and Oxidative Phosphorylation
Cellular Respiration and Oxidative Phosphorylation
# Cellular Respiration
Cellular respiration is a series of redox reactions that occur in the inner membrane of mitochondria (in eukaryotes) and the cell membrane (in bacteria). This chain is made up of 4 protein complexes, each playing a distinct role in electron transport and proton pumping out of the membrane.
1. Complex I (NADH dehydrogenase):
- Transfers 2 electrons from NADH to ubiquinone (Q).
- Pumps 4 protons from the mitochondrial matrix to the intermembrane space.
2. Complex II (Succinate dehydrogenase):
- Transfers 2 electrons from succinate/FADH2 to ubiquinone (Q).
- Does not pump protons.
3. Complex III (Ubiquinone-cytochrome c oxidoreductase):
- Transfers 2 electrons from QH2 to cytochrome c.
- Pumps 4 protons from the mitochondrial matrix to the intermembrane space.
4. Complex IV (Cytochrome oxidase):
- Transfers 4 electrons from cytochrome c to O2 to reduce O2 to H2O.
- Pumps 2 protons from the mitochondrial matrix to the intermembrane space.
Result: After 1 electron transport chain, 10 protons are pumped out of the mitochondrial matrix.
# Oxidative Phosphorylation
The proton gradient across the mitochondrial membrane creates a chemiosmotic potential used to generate ATP from ADP and inorganic phosphate (Pi) by the enzyme ATP synthase. This process is called oxidative phosphorylation.
- P/O ratio:
- P/O (NADH) = 2.5: Each NADH oxidized generates 2.5 ATP.
- P/O (FADH2) = 1.5: Each FADH2 oxidized generates 1.5 ATP.
# Role of Oxidative Phosphorylation
- Activation of organic substances
- Energy storage and transport
- Active uptake
# Krebs Cycle
The Krebs cycle is a cycle of reactions occurring in the mitochondrial matrix (in eukaryotes) and cytoplasm (in bacteria). This cycle produces ATP and NADH, FADH2, which are energy carriers for the electron transport chain.
- Starts with: AcetylCoA
- Intermediate products: Citrate, Isocitrate, ?-ketoglutarate, SuccinylCoA, Succinate, Fumarate, Malate, Oxaloacetate.
- Irreversible reactions: AcetylCoA -> Citrate, Isocitrate -> ?-ketoglutarate
- Reversible reactions: Citrate -> Isocitrate (requires aconitase enzyme)
Note: Information on the regulation of the complexes in the electron transport chain is not provided in the data.
Leave a Reply