Which enzyme initiates the breakdown of glycogen to glucose during anaerobic glycolysis in the short-term energy system?

Which enzyme initiates the breakdown of glycogen to glucose during anaerobic glycolysis in the short-term energy system?

• A. Hexokinase
• B. Glycogen phosphorylase
• C. Phosphofructokinase
• D. Pyruvate kinase

Answer: (B)

Breaking down glycogen to feed rapid energy production hinges on glycogen phosphorylase. This enzyme starts glycogenolysis by cleaving glucose units from the glycogen chain as glucose-1-phosphate, providing immediate substrate for glycolysis during intense, anaerobic efforts. The glucose-1-phosphate is then converted to glucose-6-phosphate, which enters glycolysis to generate ATP without needing to wait for glucose to be taken up from the blood. Hexokinase would act on free glucose to form glucose-6-phosphate, but it doesn’t initiate glycogen breakdown. Phosphofructokinase and pyruvate kinase are key steps later in glycolysis, not the starting point for glycogen-derived fuel.

Breaking down glycogen to feed rapid energy production hinges on glycogen phosphorylase. This enzyme starts glycogenolysis by cleaving glucose units from the glycogen chain as glucose-1-phosphate, providing immediate substrate for glycolysis during intense, anaerobic efforts. The glucose-1-phosphate is then converted to glucose-6-phosphate, which enters glycolysis to generate ATP without needing to wait for glucose to be taken up from the blood. Hexokinase would act on free glucose to form glucose-6-phosphate, but it doesn’t initiate glycogen breakdown. Phosphofructokinase and pyruvate kinase are key steps later in glycolysis, not the starting point for glycogen-derived fuel.