ITRIC 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