The cleavage of glycogen by glycogen phosphorylase releases _____.

• A. free glucose
• B. UDP-glucose
• C. glucose-6-phosphate
• D. glucose-1-phosphate

Answer: (D)

Verified step by step guidance

1. Understand the role of glycogen phosphorylase: Glycogen phosphorylase is an enzyme that catalyzes the breakdown of glycogen into glucose-1-phosphate by adding inorganic phosphate (Pi) to the terminal glucose unit of glycogen.
2. Recall the reaction mechanism: Glycogen phosphorylase performs phosphorolysis, not hydrolysis. This means it uses inorganic phosphate (Pi) to cleave the α-1,4 glycosidic bonds in glycogen, releasing glucose-1-phosphate instead of free glucose.
3. Recognize the product of the reaction: The immediate product of glycogen phosphorylase activity is glucose-1-phosphate, which is a phosphorylated form of glucose. This prevents glucose from freely diffusing out of the cell and keeps it available for further metabolism.
4. Understand the fate of glucose-1-phosphate: Glucose-1-phosphate can be converted into glucose-6-phosphate by the enzyme phosphoglucomutase, which is a key intermediate in glycolysis or other metabolic pathways.
5. Clarify why other options are incorrect: Free glucose is not directly released by glycogen phosphorylase, and UDP-glucose is involved in glycogen synthesis, not degradation. Glucose-6-phosphate is a downstream product formed after glucose-1-phosphate is processed.