Final answer:
The G-protein coupled receptor acts as the Guanine Nucleotide Exchange Factor (GEF) in G-protein coupled receptor signaling, triggering the release of GDP and the binding of GTP to the G-α subunit, which then activates downstream signaling pathways.
Step-by-step explanation:
The GEF (Guanine Nucleotide Exchange Factor) in G-protein coupled receptor signaling is 5) The G-Protein coupled receptor.
During cell signaling, the G-protein coupled receptor (GPCR) serves as the GEF. When a signaling molecule binds to the GPCR in the plasma membrane, it causes a conformational change in the receptor. This change allows the GPCR to interact with the G-α subunit, facilitating the release of GDP and binding of GTP to the G-α subunit. Upon GTP binding, the G-β and G-γ subunits dissociate from the G-α subunit, which then goes on to activate downstream effector proteins in the signaling pathway. The hydrolysis of GTP to GDP ultimately terminates the signal, and the G-protein subunits reassociate, returning to the inactive state.