The Krebs Cycle

• What is the Krebs Cycle?

  • The Krebs cycle (sometimes called the citric acid cycle) consists of a series of enzyme-controlled reactions
• Krebs cycle

  • 1.2 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
  • 2. 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
  • 3. 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

  A) acetyl coenzyme a

  B) 2c

  C) citrate

  D) 6c

  E) co2

  F) NAD

  G) reduced

  H) intermediate

  I) 5c

  J) co2

  K) nad

  L) reduced

  M) adp

  N) atp

  O) fad

  P) reduced

  Q) nad

  R) reduced

  S) oxaloacetate

  T) 4c

  
• 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