Arrange the steps of glycogenolysis in sequence: A. Formation of limit dextrins B. Transfer of glucose residues from branched chain to neighbouring straight chain (Glucan Transferase) C. Break down alpha(1-4) bond from non reducing end D. Break down of alpha (1-6)bond
## **Core Concept**
Glycogenolysis is the breakdown of glycogen to glucose, a crucial process for energy production in the body. It involves the sequential breakdown of glycogen, a complex carbohydrate stored in the liver and muscles, into glucose molecules that can be used by the body for energy. This process is vital for maintaining blood glucose levels during fasting or when glucose is in short supply.
## **Why the Correct Answer is Right**
The correct sequence of steps in glycogenolysis is as follows:
1. **Break down alpha(1-4) bond from non-reducing end (C)**: The process begins with the breakdown of alpha(1-4) glycosidic bonds from the non-reducing end of the glycogen chain by the enzyme glycogen phosphorylase. This step releases glucose-1-phosphate units.
2. **Formation of limit dextrins (A)**: As glycogen phosphorylase works, it eventually reaches a point where it cannot proceed further due to the branch points in the glycogen molecule. At this stage, the glycogen molecule is converted into limit dextrins.
3. **Break down of alpha (1-6) bond (D)**: The debranching enzyme then breaks down the alpha(1-6) glycosidic bonds at the branch points of the limit dextrins, releasing a single glucose molecule and a shortened glycogen chain.
4. **Transfer of glucose residues from branched chain to neighbouring straight chain (Glucan Transferase) (B)**: Before the debranching enzyme can act on another branch point, the glucan transferase activity of the debranching enzyme transfers three glucose residues from the branch to the main chain, allowing the phosphorylase to continue acting.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Formation of limit dextrins occurs after the initial breakdown of alpha(1-4) bonds, not first.
- **Option B:** The transfer of glucose residues by glucan transferase happens after the formation of limit dextrins and the action on alpha(1-6) bonds.
- **Option D:** The breakdown of alpha(1-6) bonds occurs after the formation of limit dextrins.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that defects in the enzymes involved in glycogenolysis, such as glycogen phosphorylase or debranching enzyme, can lead to glycogen storage diseases. These diseases result in the accumulation of glycogen in various tissues, leading to a range of clinical manifestations depending on the specific enzyme deficiency.
## **Correct Answer:** C-A-D-B.