Final answer:
Glycolysis reversed, with enzymes catalyzing backwards reactions, includes endergonic steps with positive delta G. However, gluconeogenesis is the actual process that reverses glycolysis, with reactions generally proceeding with a negative delta G, being exergonic and energetically favorable.
Step-by-step explanation:
The question inquires about the reversal of glycolysis and the free energy change (delta G) associated with such a process. If glycolysis were simply reversed and all enzymes involved could catalyze the reverse reactions, some reactions of glycolysis would have a positive delta G, meaning they are endergonic (energy-requiring). For example, the splitting of F1,6 diP into two molecules of G-3-P has a positive free energy change of +7.5 kcal/mol. However, glycolysis is essentially reversed during gluconeogenesis, under conditions such as fasting, low-carb diets, or high-protein diets like the Atkins Diet. During glycolysis in reverse or gluconeogenesis, reactions proceed with a negative delta G, meaning they are exergonic (energy-releasing) and thermodynamically favorable.
Gluconeogenesis recycles the products of glycolysis back into glucose, using similar, yet distinct, enzymes for certain steps where the direct reverse reaction of glycolysis is too energetically unfavorable to proceed. Despite the energetically unfavorable steps in the direct reversal of glycolysis, glycolysis itself is a spontaneous and energetically favorable pathway that proceeds with an overall negative delta G, particularly in actively respiring cells.