Final answer:
The enzyme that exerts the most control on glycolysis is phosphofructokinase. It regulates the pace of glycolysis in response to the energy needs of the cell, being inhibited by high levels of ATP and stimulated by lower ATP levels or higher AMP levels.
Step-by-step explanation:
The control of glycolysis is most significantly exerted at the phosphofructokinase step, which is the key regulatory point in the pathway. This enzyme is sensitive to various feedback signals such as high levels of ATP, citrate, and a lower pH, all of which can decrease the enzyme's activity. Conversely, a decrease in ATP or an increase in AMP can activate it. While other enzymes like hexokinase and pyruvate kinase play roles in glycolysis regulation, phosphofructokinase is considered the main control point because it acts as a gatekeeper for the further commitment of glucose to glycolysis, and its activity has a pronounced effect on the overall rate of glycolysis.