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Citric Acid Cycle

Citric Acid Cycle

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CITRIC ACID CYCLE (aka Krebs cycle and tricarboxylic acid cycle)
  • Occurs under aerobic conditions (has many exits and entry points)
  • Occurs in the mitochondrial matrix (pyruvate transported from cytosol)
  • First intermediate is Acetyl CoA (two carbon molecule)
  • 8 more intermediates to complete the cycle: Oh, Can I Keep Studying Science For Med-school?
ACETYL CoA
  • 2-carbon molecule
  • Can come from carbohydrates (via pyruvate), fatty acids and amino acids
  • Pyruvate dehydrogenase complex: Pyruvate + NAD + --> Acetyl CoA + CO2 + NADH
CITRATE AND ISOCITRATE
  • 6-carbon molecules
  • Oxaloacetate (4 carbons) + Acetyl CoA (2 carbons) = Citrate
  • Isomerized to form isocitrate
ALPHA-KETOGLUTARATE
  • 5-carbon molecule
  • 1 carbon dioxide and 1NADH released in its production
SUCCINYL CoA
  • 4-carbon molecule
  • 1 carbon dioxide and 1 NADH released in its production
SUCCINATE
  • 4-carbon molecule
  • Lost CoA and 1 ATP produced via substrate level phosphorylation
FUMARATE
  • 4-carbon molecule
  • FADH2 released in its production (F for FADH2 and Fumarate)
MALATE TO OXALOACETATE
  • Last reaction in the cycle
  • Both are 4-carbon molecules
  • Last NADH released in the cycle
TOTAL OUTPUT:
  • Pyruvate decarboxylation: 1 NADH and 1 carbon dioxide
(x2 per glucose)
  • Per turn: 2 carbon dioxide molecules, 3 NADH and 2 FADH2
(2 turns per glucose)
  • NADH and FADH2 deliver electrons to electron transport chain on inner mitochondrial membrane

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