Glycogenolysis is best described by which of the following statements:
**Core Concept**
Glycogenolysis is the breakdown of glycogen, a complex carbohydrate stored in the liver and muscles, into glucose. This process is catalyzed by the enzyme glycogen phosphorylase, which is activated by epinephrine and glucagon.
**Why the Correct Answer is Right**
Glycogenolysis involves the sequential removal of glucose residues from the glycogen molecule, resulting in the formation of glucose-1-phosphate. This process is initiated by the action of glycogen phosphorylase, which catalyzes the transfer of a phosphate group from ATP to the terminal glucose residue of the glycogen molecule. The resulting glucose-1-phosphate is then converted to glucose-6-phosphate by the enzyme phosphoglucomutase.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the key enzyme involved in glycogenolysis.
**Option B:** This option is incorrect because it suggests that glycogenolysis is primarily regulated by insulin, which is actually a hormone that promotes glycogen synthesis.
**Option C:** This option is incorrect because it implies that glycogenolysis is a passive process, whereas it is actually an active process that is catalyzed by the enzyme glycogen phosphorylase.
**Clinical Pearl / High-Yield Fact**
Glycogenolysis is an important mechanism for maintaining blood glucose levels during periods of fasting or intense physical activity. It is also a key component of the body's response to stress, as it allows the liver to rapidly mobilize glucose stores in response to the release of epinephrine and other stress hormones.
**Correct Answer:** C. Glycogenolysis is catalyzed by the enzyme glycogen phosphorylase, which is activated by epinephrine and glucagon.