There are two main types of phosphorylation in biological processes: substrate-level phosphorylation and oxidative phosphorylation. Here’s a summary:
Substrate-Level Phosphorylation
• Definition: ATP is produced directly by the transfer of a phosphate group from a phosphorylated substrate to ADP.
• Process: This transfer is catalyzed by an Enzyme.
• Location:
• Occurs in the cytoplasm during Glycolysis.
• Occurs in the mitochondrial matrix during The Krebs Cycle.
• energy Source: Does not require oxygen; instead, it relies on high-energy intermediates.
• Efficiency: Produces smaller amounts of ATP compared to oxidative phosphorylation.
• Examples:
• Glycolysis: Phosphoenolpyruvate (PEP) donates a phosphate to ADP, forming ATP.
• Krebs cycle: Succinyl-CoA donates a phosphate group to GDP (or ADP).
Oxidative Phosphorylation
• Definition: ATP is produced through the Electron Transport Chain (ETC) and Chemiosmosis, using a Proton Gradient across a membrane.
• Process:
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High-energy electrons from NADH and FADH₂ are transferred through a series of proteins in the ETC.
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This movement powers the pumping of protons (H⁺) across the inner mitochondrial membrane.
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Protons flow back into the matrix through ATP Synthase, driving the synthesis of ATP from ADP and inorganic phosphate (Pi).
• Location: Inner mitochondrial membrane (eukaryotes) or plasma membrane (prokaryotes).
• energy Source: Requires oxygen as the final electron acceptor, forming water.
• Efficiency: Produces the majority of ATP in Cellular Respiration (~34 ATP per Glucose molecule).