Correct option is A
Explanation-
Epinephrine is a hormone released during stress or low blood glucose. It triggers a cascade of intracellular events that ultimately break down glycogen (a stored form of glucose) into glucose-1-phosphate, which is then used to raise blood glucose levels.
Step 1: Activation of G Protein (Gₛα)
(Corresponds to statement A)
Epinephrine binds to a β-adrenergic receptor (a G protein-coupled receptor, GPCR) on the surface of liver cells. This causes a conformational change in the receptor. The receptor activates an intracellular G protein (specifically the Gₛα subunit). Gₛα exchanges GDP for GTP and becomes active.
Step 2: Adenylyl Cyclase Activation
(Corresponds to statement D)
The active Gₛα-GTP complex binds to and activates adenylyl cyclase, an enzyme embedded in the plasma membrane. Adenylyl cyclase acts as the amplifier in this signaling pathway.
Step 3: Second Messenger Generation (cAMP)
(Corresponds to statement C)
Adenylyl cyclase converts ATP to cyclic AMP (cAMP). cAMP is a second messenger, meaning it carries the signal inside the cell and activates downstream targets.
Step 4: Protein Kinase A (PKA) Activation
(Corresponds to statement B)
cAMP binds to the regulatory subunits of protein kinase A (PKA). This causes the release of active catalytic subunits of PKA. PKA then phosphorylates several key enzymes involved in glycogen metabolism.
Final Biological Effect
PKA activates phosphorylase kinase, which then activates glycogen phosphorylase. Glycogen phosphorylase breaks down glycogen into glucose-1-phosphate. Glucose-1-phosphate is converted to glucose-6-phosphate, and eventually glucose, which is released into the blood.
So the correct option is a -
A → D → C → B
