Final answer:
When epinephrine binds to a G protein-coupled receptor in the cell membrane, it triggers a series of events that ultimately lead to cell-specific responses. The binding of epinephrine causes a conformational change in the receptor, allowing it to interact with a G-protein. This activation of G-protein leads to the production of cyclic AMP (cAMP), which acts as a second messenger.
Step-by-step explanation:
When epinephrine, a first messenger, binds to a G protein-coupled receptor in the cell membrane, it triggers a series of events. First, the binding of epinephrine causes a conformational change in the receptor, which allows it to recognize and bind to a G-protein trimer on the cytoplasmic surface of the plasma membrane. Once the G-protein is bound, GDP is replaced by GTP on the alpha subunit of the G-protein, causing it to dissociate from the beta and gamma subunits. The GTP-bound alpha subunit can then bind to and activate an enzyme called adenylyl cyclase. Adenylyl cyclase converts ATP to cyclic AMP (cAMP), which acts as a second messenger in the cell. cAMP can then mediate a cell-specific response by activating protein kinase A (PKA), which phosphorylates target proteins and brings about a cellular response. In the case of epinephrine binding to its receptor, this can lead to glycogen breakdown, increased cellular metabolism, and other cellular responses. It's important to note that the action of cAMP is terminated by an enzyme called phosphodiesterase, which breaks down cAMP into inactive products, thus terminating the signal.