Final answer:
The synthesis of stearate from acetyl-CoA requires an investment of ATP and NADPH during the fatty acid synthesis process. By contrast, degradation of stearate to acetyl-CoA generates a significant amount of ATP as acetyl-CoA enters the citric acid cycle and NADH and FADH2 contribute during oxidative phosphorylation, overall resulting in a high energy yield.
Step-by-step explanation:
The energy cost of synthesizing stearate from mitochondrial acetyl-CoA compared to the energy recovered by degrading stearate to acetyl-CoA involves a complex balance of energy investment and energy yield. For the synthesis of stearate, a series of reactions occurs requiring investment of ATP and NADPH.
In contrast, the breakdown of stearate through ß-oxidation and further metabolism via the citric acid cycle and electron transport chain results in a significant production of ATP. The synthesis involves activation of acetyl-CoA to malonyl-CoA, which costs 1 ATP.
Subsequently, each extension of the fatty acid chain by two carbons, up to stearate (18 carbons), requires further ATP and NADPH. Upon the complete breakdown of stearate, after activation (which uses 2 high-energy bonds in ATP, converting it to AMP), each of the resulting acetyl-CoA molecules enters the citric acid cycle, with NADH and FADH₂ produced during ß-oxidation also contributing to ATP generation via oxidative phosphorylation. Notably, the energy yield from the complete oxidation of one mole of stearic acid is 120 mole of ATP, which is substantially higher than the yield from glucose oxidation.