The Krebs cycle

• the Krebs cycle produces reduced coenzymes and ATP

  it involves a series of oxidation-reduction reactions

  take place in the matrix of the mitochondria

  cycle happens 2x for every pyruvate molecule
• 1. formation of a 6-carbon compound:
  2. acetyl CoA from the link reaction combines with a four carbon molecule (oxaloacetate) to form a 6-carbon molecule (citrate)
  3. coenzyme A goes back to the link reaction to be used again
• 1. (2) Formation of a 5-carbon compound
  2. the 6-carbon citrate molecule is converted to a 5-carbon molecule
  3. decarboxylation occurs, where carbon dioxide is removed
  4. dehydrogenation also occurs
  5. the hydrogen is used to produce reduced NAD from NAD
• 1. (3) regeneration of oxaloacetate:
  2. the 5-carbon molecule is then converted to a 4-carbon molecule
  3. there are some intermediate compounds formed during this conversion
  4. decarboxylation and dehydrogenation occur - producing one molecule of FADH and 2x NADH
  5. ATP is produced by the direct transfer of a phosphate group from an intermediate compound to ATP
  6. citrate has now been converted into oxaloacetate
• when a phosphate group is directly transferred from one molecule to another - substrate-level phosphorylation
• 1 coenzyme A - reused in the next link reaction

  oxaloacetate - regenerated for use in the next Krebs cycle

  2 co2 - released as a waste product

  1 ATP - used for energy

  3 reduced NAD - to oxidative phosphorylation

  1 reduced FAD - to oxidative phosphorylation
• coenzyme A transfers acetate between molecules
• dehydrogenation is the removal of hydrogen from a molecule
• the Krebs cycle turns twice for one molecule of glucose