g Glucagon is a hormone that is released when the level of glucose in the blood is low. Glucagon uses a G protein signalling pathway to promote glycogenolysis. Put the steps of the signal transduction pathway in order after the release of glucagon into the blood before glycogen phosphorylase is activated leading to glycogenolysis. 1. Glucagon binds extracellularly to G protein-coupled receptor. 2. G protein releases GDP and binds GTP. 3. Activated G protein activates adenylyl cyclase. 4. Adenylate cyclase converts ATP to cAMP. 5. Cyclic AMP activates protein kinase A.