Question

Identify the correct sequence of the Regulatory cascade of controlling glycogen breakdown. A. The active C Monomer of PKA activates Phosphorylase b kinase. B. Active Phosphorylase a catalyzes glycogen breakdown. C. Hormone binding activates adenylate cyclase. D. The active kinase converts the inactive phosphorylase b to active phosphorylase a. E. cAMP binds to the R-subunits of the PKA \(R_2C_2\) tetramer, causing their dissociation from C sub-units.

• A. A, B, E, D, C
• B. A, C, D, E, B
• C. C, D, A, E, B
• D. C, E, A, D, B

Hint:

For glycogen breakdown cascade, remember the order: Hormone \(\rightarrow\) cAMP \(\rightarrow\) PKA \(\rightarrow\) phosphorylase kinase \(\rightarrow\) phosphorylase a \(\rightarrow\) glycogen breakdown.

Answer 1

The Correct Option is D

Concept:
Glycogen breakdown is controlled by a hormonal signaling cascade. This cascade involves hormone binding, formation of cAMP, activation of protein kinase A, activation of phosphorylase kinase, and finally activation of glycogen phosphorylase.

Step 1: Hormone binding starts the process.
The first event is hormone binding to its receptor. This activates adenylate cyclase. \[ \text{First step} = C \]

Step 2: cAMP activates PKA.
Adenylate cyclase increases cAMP level. cAMP binds to the regulatory subunits of PKA and causes dissociation of catalytic subunits. \[ \text{Second step} = E \]

Step 3: Catalytic subunit of PKA activates phosphorylase b kinase.
The active catalytic monomer of PKA phosphorylates and activates phosphorylase b kinase. \[ \text{Third step} = A \]

Step 4: Phosphorylase b is converted into phosphorylase a.
The active kinase converts inactive phosphorylase b into active phosphorylase a. \[ \text{Fourth step} = D \]

Step 5: Glycogen breakdown occurs.
Active phosphorylase a catalyzes the breakdown of glycogen. \[ \text{Fifth step} = B \] Therefore, the correct sequence is: \[ C, E, A, D, B \] \[ \therefore \text{Correct Answer is (D)} \]