Enzyme involved in both glycogenesis and glycogenolysis is:
**Core Concept**
The question tests the student's knowledge of enzymes involved in glycogen metabolism, specifically those that participate in both glycogenesis (glycogen synthesis) and glycogenolysis (glycogen breakdown). Glycogen is a complex carbohydrate stored in the liver and muscles, and its metabolism is crucial for maintaining blood glucose levels.
**Why the Correct Answer is Right**
The enzyme involved in both glycogenesis and glycogenolysis is glycogen synthase. This enzyme is responsible for adding glucose molecules to the growing glycogen chain during glycogenesis. Conversely, during glycogenolysis, glycogen synthase is converted to its inactive form, allowing glycogen phosphorylase to break down glycogen into glucose-1-phosphate. This dual role of glycogen synthase highlights its central position in glycogen metabolism.
**Why Each Wrong Option is Incorrect**
* **Option A:** Glycogen phosphorylase is primarily involved in glycogenolysis, breaking down glycogen into glucose-1-phosphate. It is not directly involved in glycogenesis.
* **Option B:** Debranching enzyme is involved in glycogenolysis, specifically in breaking the alpha-1,6-glycosidic bonds in glycogen. However, it is not involved in glycogenesis.
* **Option D:** Phosphoglucomutase is an enzyme involved in glycogenolysis, converting glucose-1-phosphate to glucose-6-phosphate. However, it is not directly involved in glycogenesis.
**Clinical Pearl / High-Yield Fact**
Glycogen synthase is a key regulatory enzyme in glycogen metabolism, and its activity is tightly controlled by hormones such as insulin and glucagon. Insulin activates glycogen synthase, promoting glycogen synthesis, while glucagon inhibits glycogen synthase, promoting glycogen breakdown.
**Correct Answer:** C. Glycogen synthase. Glycogen synthase.