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How much ATP is formed when a 17-carbon molecule undergoes beta-oxidation?
What to do:
STEP 1:
Start by letting n = number of carbons.
The number of rounds in the β-oxidation and the number of acetyl-CoA molecules produced can be found using:
• (n/2) - 1.5
Additionally, 1 propionyl-CoA (3-carbon Acetyl-CoA) is produced in the last round.
Based on a yield of 3 ATP per NADH and 2 ATP per FADH2 that are oxidized in the respiratory chain:
• Multiply the number of rounds by 3, then multiply by 2: take its sum.
• Multiply the number of acetyl-CoA by 12 ATP / acetyl-CoA (since each Acetyl CoA yields 12 ATP when oxidized in the Krebs Cycle)
• Subtract now two ATP (-2 ATP) consumed in the initial activation of the fatty acid
STEP 2: What happens with this propionyl-CoA?
The propionyl-CoA must undergo a carboxylation in a sequence of reactions requiring Biotin and Vitamin B12. These reactions produce succinyl-CoA at a cost of 1 ATP (consider it as -1 ATP).
The conversion of propionyl-CoA to succinyl-CoA is an anaplerotic reaction (chemical reactions that form intermediates of another metabolic pathway) because the molecule of succinyl-CoA continues in the Krebs Cycle generating oxalacetate in the following sequence of reactions:
• Succinyl CoA + GDP + (P) → Succinate + CoA + GTP (equivalent to 1 ATP)
• Succinate + FAD → Fumarate + FADH2 (Generates 2 ATP in the Respiratory Chain)
• Fumarate + H2O → Malate
• Malate + NAD+ → Oxalacetate + NADH (Generates 3 ATP in the Respiratory Chain)
This suggests that the incorporation of the succinyl-CoA originated from the propionyl-CoA has generated 6 additional ATPs.
Негізгі бет How to calculate the number of ATP molecules produced during beta oxidation (Odd chain)
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