Why is it necessary to add energy to the beginning of glucose metabolism?
Glucose metabolism starts from energy-requiring reactions. Phosphate groups are added at the hydroxyl groups on C-6 and C-1 resulting in fructose bisphosphate. In the preparatory phase of glycolysis the energy of ATP is invested, raising the free-energy content of the intermediates. These priming reactions help drive the pathway in the direction of glycolysis since the reverse reactions are thermodynamically favored in the absence of ATP.