Final answer:
The conversion of fructose-6-phosphate into fructose-1,6-bisphosphate is irreversible largely due to a highly negative free energy change facilitated by the enzyme phosphofructokinase, making it a committed step in glycolysis.
Step-by-step explanation:
The conversion of fructose-6-phosphate (F-6-P) into fructose-1,6-bisphosphate (F1,6 diP) is catalyzed by the enzyme phosphofructokinase. This reaction is considered irreversible due to its highly negative free energy change (ΔG), indicating a strong thermodynamic drive to proceed in one direction.
This negative free energy change makes the reaction practically irreversible under normal physiological conditions.
The enzyme adds a second phosphate group from ATP to fructose-6-phosphate, making fructose-1,6-bisphosphate, and this step is also known as the committed step in the glycolytic pathway because it is highly regulated and effectively commits the substrate to following through the rest of the pathway.