When epinephrine binds to its GPCR activating the cAMP cascade, all of the following happen EXCEPT:

• A. GDP dissociates from the G protein as GTP associates.
• B. The alpha-subunit of the G protein activates adenylate cyclase and cAMP is produced.
• C. G protein is activated and diffuses away from the cell membrane into the nucleus.
• D. The alpha-subunit of the G protein hydrolyzes GTP and becomes inactive.
• E. The alpha-subunit of the G protein bound to GDP reassociates with the beta & gamma-subunits.

Answer: (C)

Verified step by step guidance

1. Understand the role of epinephrine in activating the GPCR (G-protein coupled receptor) and initiating the cAMP cascade. Epinephrine binds to the receptor, causing a conformational change that activates the G protein.
2. Recognize the process of G protein activation. When the GPCR is activated, the GDP bound to the alpha-subunit of the G protein is replaced by GTP, activating the G protein.
3. Identify the role of the alpha-subunit of the G protein. Once activated, the alpha-subunit dissociates from the beta and gamma subunits and interacts with adenylate cyclase, leading to the production of cAMP.
4. Understand the inactivation process of the G protein. The alpha-subunit eventually hydrolyzes GTP to GDP, which leads to its reassociation with the beta and gamma subunits, rendering the G protein inactive.
5. Clarify the incorrect statement: The G protein does not diffuse away from the cell membrane into the nucleus. It remains associated with the membrane, where it performs its signaling functions.