How many molecules of ATP are obtained from the β-oxidation...

Key Concepts

?-oxidation

?-oxidation is the mitochondrial process by which fatty acids are broken down into two?carbon units called acetyl-CoA. This process involves a series of dehydrogenation, hydration, oxidation, and thiolysis reactions that not only release acetyl-CoA but also produce reduced cofactors (NADH and FADH2), which are subsequently used in the electron transport chain to generate ATP.

Number of ?-oxidation Cycles

For fatty acids with an even number of carbons, such as a 16?carbon fatty acyl-CoA, the number of ?-oxidation cycles is calculated as (n/2) - 1. This determines how many rounds of reactions occur where each cycle yields one NADH and one FADH2, while also progressively cleaving off acetyl-CoA units.

Acetyl-CoA Production

In each cycle of ?-oxidation, one molecule of acetyl-CoA is produced, with the final cycle yielding an additional acetyl-CoA. For a 16-carbon fatty acid, this results in eight molecules of acetyl-CoA, which are key substrates for the citric acid cycle and play a central role in cellular energy production.

ATP Yield from Reduced Cofactors

The NADH and FADH2 generated during ?-oxidation are crucial because they donate electrons to the electron transport chain, where energy is conserved in the form of ATP. The established P/O ratios (commonly approximated as 3 ATP per NADH and 2 ATP per FADH2) are used to calculate how much ATP is produced from these reducing equivalents.

Overall ATP Yield Calculation

To determine the total ATP yield from the complete oxidation of a fatty acid, one must integrate the ATP produced directly from the ?-oxidation steps (through the generation of NADH and FADH2) as well as the additional ATP obtained from the subsequent oxidation of acetyl-CoA in the citric acid cycle. This comprehensive calculation also takes into account the ATP cost involved in the activation of the fatty acid to its CoA derivative.

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