Phosphorylation: Substrate Level vs Oxidative

Overview of Phosphorylation

• Definition: Phosphorylation is the transfer of a phosphate group to a molecule or protein.
• Catalysis: Typically catalyzed by enzymes known as kinases.
  • Kinases use ATP to add a phosphate group to other molecules, converting ATP to ADP in the process.

Substrate Level Phosphorylation

• Occurs in: Glycolysis and the TCA cycle.
• Mechanism: Direct transfer of a phosphate group from a substrate to ADP, forming ATP.
  • Example: 1,3-bisphosphoglycerate transfers a phosphate to ADP to form ATP and 3-phosphoglycerate.
• Enzymes: Catalyzed by specific kinases.
  • Different kinases are named based on their specific reactions.
• Energy Source: High-energy intermediates containing phosphates.
• Reversibility: The reaction can often work in reverse by using ATP to phosphorylate substrates.
• Recognition: Occurs when phosphates are donated from a substrate molecule.

Oxidative Phosphorylation

• Occurs in: Electron Transport Chain (ETC) on the mitochondrial inner membrane.
• Mechanism: Uses electron carriers (NADH, FADH2) and oxygen to create a force that synthesizes ATP from ADP and inorganic phosphate (Pi).
  • ETC: A series of enzyme complexes that facilitate this process.
  • The oxidation of NADH and FADH2 results in water production as electrons and protons are combined with oxygen.
  • The energy generated is used by ATP synthase to synthesize ATP.
• Distinct Feature: Unlike substrate level, does not involve direct phosphate transfer from a substrate.
• Byproducts: Water is a main byproduct of oxidative phosphorylation.

Comparison and Context

• Both Processes: Involve ATP synthesis.
• Substrate Level:
  • Occurs in glycolysis and TCA.
  • Involves direct phosphate transfer from a reactant.
• Oxidative:
  • Occurs in the ETC.
  • Involves oxidative energy to synthesize ATP.
• Recognition: Ability to identify reactions as either substrate level or oxidative is crucial.
• Stages of Occurrence:
  • Know which stages of cellular respiration each type occurs in.

Summary

• Understanding the differences and specific contexts of substrate level and oxidative phosphorylation is essential.
• Be able to identify reactions and correctly classify them based on the type of phosphorylation involved.