• The Krebs cycle (sometimes called the citric acid cycle) consists of a?series of enzyme-controlled reactions
• 2 carbon (2C) Acetyl CoA?enters the circular pathway from the?link reaction?in glucose metabolism
  • Acetyl CoA formed from?fatty acids?(after the breakdown of lipids)?and?amino acids?enters directly into the Krebs Cycle from other metabolic pathways

   

• 4 carbon (4C)?oxaloacetate?accepts the 2C acetyl fragment from acetyl CoA to form the 6 carbon (6C)?citrate
  • Coenzyme A is released in this reaction

   

• Citrate is then converted back to oxaloacetate?through a series of oxidation-reduction (redox) reactions

The Krebs Cycle uses acetyl CoA from the link reaction and the regeneration of oxaloacetate to produce reduced NAD, reduced FAD and ATP

Regeneration of Oxaloacetate

• Oxaloacetate is regenerated in the Krebs cycle through a series of?redox reactions
• Decarboxylation?of citrate
• • Releasing?2 CO2?as waste gas

   

• Oxidation?(dehydrogenation) of citrate
  • Releasing H atoms that?reduce coenzymes NAD and FAD
  • 3 NAD and 1 FAD →?3NADH + H+?and 1 FADH2

   

• Substrate-linked phosphorylation
  • A phosphate is transferred from one of the intermediates to ADP, forming?1 ATP