Final answer:
If glycogenesis and glycogenolysis occurred at the same time, a futile cycle would result, leading to energy waste and no change in glycogen levels. This is prevented by the tight regulation of metabolic pathways.
Step-by-step explanation:
If both glycogen synthesis (glycogenesis) and glycogen breakdown (glycogenolysis) were active simultaneously in a cell, there would be a futile cycle. A futile cycle occurs when two opposing pathways run at the same time, leading to a waste of energy in the form of ATP and no net change in the amount of glycogen. Such simultaneous activity would disrupt metabolic equilibrium and drain cellular resources without providing any benefit, as energy would be expended in both building up and breaking down glycogen.
This scenario is prevented in cells because the metabolic pathways of glycolysis (where glucose is broken down to pyruvate) and gluconeogenesis (where glucose is synthesized) are tightly regulated. These processes are normally reciprocal to each other; one pathway is active while the other is inhibited, which is essential for efficient energy usage and maintaining glucose homeostasis. This regulation ensures that no unnecessary expenditure of energy occurs.