Rank these reactions from least to most energetically favorable.

Rank the options below.

Glucose-6-P to Fructose-6-P, + 0.4 kcal/mol

ATP to ADP and Pi, - 7.3 kcal/mol

Glucose to Glucose-6-P, + 3.3 kcal/mol

PEP to pyruvate, - 14.8 kcal/mol

From least to most energetically favorable, the reactions are:

Glucose to Glucose-6-P (least); Glucose-6-P to Fructose-6-P; ATP to ADP and Pi; PEP to pyruvate (most favorable)

Explanation:

ΔG represents the free energy change that occurs during a chemical reaction. A reaction with negative free energy change is exergonic and spontaneous. Negative free energy change represents the fact that reactants have more free energy than products. The excess of the energy is released during the reaction and makes it a spontaneous process.

q'On the other hand, a reaction with positive free energy change is endothermic and non-spontaneous. These thermodynamically unfavorable reactions are coupled with other exergonic reactions to make them occur.

Among the given example, PEP to pyruvate has the highest negative free energy change (-14.8 kcal/mol) and therefore, is energetically most favorable. On the other hand, "Glucose to Glucose-6-P" has the highest positive free energy charge (+3.3 kcal/mol) making it energetically the most unfavorable reaction.