Enter your Substrate Type, Number of Carbon Atoms, Double Bonds, and Substrate Amount, then toggle Include Activation Cost and adjust Pathway Efficiency to calculate your Total ATP Yield — along with ATP per Substrate Molecule, Theoretical Maximum, and Efficiency Loss so you can see exactly where the energy goes.
Total ATP Yield
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ATP per Substrate Molecule
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Theoretical Maximum
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Efficiency Loss
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For even-numbered saturated fatty acids, use the formula: ATP = (7C - 6 - 1.5D) - 2(D-2), where C is carbon atoms and D is double bonds. This accounts for beta-oxidation cycles, citric acid cycle, and electron transport chain.
The theoretical maximum is 38 ATP molecules per glucose (2 from glycolysis, 2 from citric acid cycle, 34 from electron transport). However, the realistic yield is about 30-32 ATP due to transport costs and inefficiencies.
Unsaturated fatty acids require additional enzymes and bypass certain steps in beta-oxidation, reducing the total FADH2 production. Each double bond typically reduces the ATP yield by about 1.5 molecules.
Substrate activation consumes ATP initially. For example, fatty acid activation requires 2 ATP equivalents, and this cost must be subtracted from the total yield to get the net ATP production.
Real cellular conditions include proton leak across membranes, transport costs, incomplete oxidation, and competing metabolic pathways. This typically reduces theoretical yields by 20-30%.
Odd-numbered fatty acids produce one propionyl-CoA that converts to succinyl-CoA, yielding additional ATP. The formula is: ATP = (7C - 19 - 1.5D) - 2(D-2), accounting for the extra conversion steps.
Gross ATP yield is the total ATP produced during metabolism. Net ATP yield subtracts the ATP consumed for activation and transport, giving the actual energy gain for the cell.