The Krebs Cycle

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The Krebs Cycle

• Occurs in the matrix of the mitochondrion
• Aerobic phase (requires oxygen)
• 2-carbon acetyl CoA joins with a 4-carbon
  compound to form a 6- carbon compound called
  Citric acid

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• Citric acid (6C) is gradually converted back to
  the 4-carbon compound
• -ready to start the cycle once more
• The carbons removed are released as CO2
• -enzymes controlling this process called
  decarboxylases
• The hydrogens, which are removed, join with NAD
  to form NADH2
• -enzymes controlling the release of hydrogen are
  called dehydrogenases

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The Cytochrome System

• 6 points along pathway where hydrogen is released
  and temporarily bound to NAD
• Reduced coenzyme NADH2 transfers hydrogen to a
  chain of hydrogen carriers called cytochrome
  system
• These systems are attached to the cristate of
  every mitochondrion

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• Transfer of hydrogen from each NADH2 along system
• -produces 3 ATP
• -process called oxidative phosphorylation
• Complete oxidation of glucose yields 38 ATP
• -2 during glycolysis
• -36 during oxidative phosphorylation

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The role of oxygen

• Final hydrogen acceptor
• Combines to form water
• Controlled by enzyme cytochrome oxidase
• Presence of oxygen also essential for hydrogen to
  pass along the cytochrome system

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