Glycogenolysis refers to the breakdown of glycogen into glucose.

• A. Synthesis of glycogen
• B. Breakdown of glycogen into glucose
• C. Breakdown of glucose into lactic acid
• D. Conversion of glucose to glycogen

Answer: (B)

Glycogenolysis is the process of breaking glycogen down into glucose. Glycogen is the stored form of glucose in the liver and muscles. When energy is needed, enzymes cleave glucose units from glycogen: glycogen phosphorylase removes glucose units as glucose-1-phosphate, which is then converted to glucose-6-phosphate. In the liver, glucose-6-phosphatase converts this to free glucose that can enter the bloodstream to raise blood glucose levels; in muscle, the glucose-6-phosphate typically powers glycolysis for local energy.

This is the opposite of glycogenesis, which is the synthesis of glycogen from glucose for storage. Breaking glucose into lactic acid describes glycolysis with anaerobic fermentation, not glycogen breakdown. Converting glucose to glycogen is glycogenesis, not glycogenolysis.