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Chapter 3: Problem 20

The acyl-Co.A synthetase reaction activates fatty acids for oxidation in cells: \\[ \mathrm{R}-\mathrm{COO}^{-}+\mathrm{CaASH}+\mathrm{ATP} \longrightarrow \mathrm{R}-\mathrm{COSCOA}+\mathrm{AMP}+\text { pyrophosphate } \\] The reaction is driven forward in part by hydrolysis of ATP to AMP and pyrophosphate. However, pyrophosphate undergoes further cleavage to yield two phosphate anions. Discuss the energetics of this reaction both in the presence and absence of pyrophosphate cleavage.

Short Answer

Expert verified
Pyrophosphate cleavage plays a critical role in the energetics of acyl-CoA synthetase reaction. In its presence, it provides enough energy to move the reaction forward as it is highly exergonic. However, in its absence, the ATP hydrolysis to AMP is not sufficiently exergonic to push the reaction forward, making the activation of fatty acids less favorable.

Step by step solution

01

Understanding the Reaction Mechanism

First, it's required to recognize the given chemical reaction: \[ R-COO^{-} + CoASH + ATP \rightarrow R-COSCoA + AMP + \text{pyrophosphate} \] where R represents the fatty acid. In this reaction, the fatty acid is activated for oxidation, turning the incoming ATP to AMP, and pyrophosphate.
02

Energetics with Presence of Pyrophosphate Cleavage

The formed pyrophosphate is further hydrolyzed into two inorganic phosphate ions. This cleavage of pyrophosphate is a highly exergonic reaction (releases energy), which further drives the reaction forward, making the overall process favorable. Therefore, the presence of pyrophosphate cleavage provides sufficient energy, thus promoting the acyl-CoA synthetase reaction.
03

Energetics in Absence of Pyrophosphate Cleavage

Without the pyrophosphate cleavage, the activation of fatty acids becomes less favorable since the hydrolysis of ATP to AMP is not sufficiently exergonic to drive the reaction forward on its own. This implies that the breakdown of ATP into AMP and pyrophosphate does not release enough energy needed for the activation of fatty acids, making the progress of the reaction less likely.

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