Link Reaction and Krebs Cycle

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Link Reaction

The Link Reaction (Mitochondrial Matrix)

  • Pyruvate dehydrogenase removes hygrogen atoms from pyruvate. It is dehydrogenated.
  • Pyruvate decarboxylase removes a carboxyl group (which becomes carbon dioxide) from pyruvate. It is decarboxylated.
  • NAD accepts the hydrogen atoms.(becomes reduced NAD)
  • Coenzyme A accepts acetate to become acetyl coenzyme A.

CoA carries acetate to the Krebs Cycle.

No ATP is produced

reduced NAD takes hydrogen atoms to inner mitochondrial membrane for oxidative phosphorylation.

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Krebs Cycle

The Krebs Cycle (Mitochondrial Matrix)

  • Acetate is offloaded from CoA and joins oxaloacetate (4C) to form citrate (6C)
  • Citrate is decarboxylated  and dehydrogenated to form a 5C compound. The hydrogen atoms are accepted by NAD. 
  • The 5C compound is decarboxylated and dehdrogenated to form a 4C compound and another molecule of reduced NAD.
  • The 4C compound is changed to another 4C compound. ADP is phosphorylated to produce ATP (substrate level phosphorylation)
  • The second 4C compound is changed to another 4C compound. A pair of hydrogen atoms are removed by FAD.
  • The third 4C compound is further dehydrogenated and regenerates oxaloacetate. Another molecule of NAD is reduced.

2 turns of the cycle = one molecule of glucose.

Products: 6 reduced NAD, 2 reduced FAD, 4 CO2, 2 ATP (for one glucose)

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