The de-phosphorylation of phosphoenolpyruvate (PEP) to form pyruvate has a change in Gibb’s free energy (ΔG) of -61.9 kJ/mol. How would you describe the reaction?

Question

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Question restatement: The de-phosphorylation of phosphoenolpyruvate (PEP) to form pyruvate has a change in Gibb’s free energy (ΔG) of -61.9 kJ/mol. How would you describe the reaction?

Option evaluations:

a. Slightly exergonic
This would imply a small negative ΔG, indicating a reaction that releases a little energy but not much. A ΔG of -61.9 kJ/mol is far more negative than what would be considered 'slightly' exergonic, so this characterization underestimates the driving force of the reaction.

b. Slightly endergonic
An endergonic process has a positive ΔG, meaning it requires input of energy. Since the given ΔG is negative, the process does not require energy input; it releases energy instead. Therefore this option is incorrect.

c. Highly exergonic
A highly exergonic reaction is one with a substantially negative ΔG, indicating a strong tendency to proceed spontaneously and release a large amount of energy. With ΔG = -61.9 kJ/mol, this is a substantial negative value characteristic of a strongly exergonic step, which is consistent with the high-energy substrate (PEP) donating phosphate and converting to pyruvate.

d. Highly endergonic
This option describes a reaction with a large positive ΔG, i.e., strongly non-spontaneous and requiring energy input. Since the given ΔG is negative, this option contradicts the thermodynamics of the reaction and is incorrect.

Putting the pieces together, the magnitude and sign of ΔG (-61.9 kJ/mol) clearly indicate a large, favorable release of free energy, i.e., a highly exergonic process. The other options fail to match the negative ΔG value or mischaracterize the thermodynamics of the reaction.

The de-phosphorylation of phosphoenolpyruvate (PEP) to form pyruvate has a change in Gibb’s free energy (ΔG) of -61.9 kJ/mol. How would you describe the reaction?

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