Question

Upon binding of epinephrine to β-adrenergic receptor, a conformational change is propagated from its extracellular face to its intracellular face leading to release of the G⍺ subunit and subsequent binding of GTP and activation of downstream components of the pathway.  What prevents G⍺ from indefinitely activating the fight-or-flight response?

1. Cleavage of G⍺ subunits by Thrombin.
2. ATIII.
3. Intrinsic GTPase activity.
4. GAPs
5. GEFs

Which components of GPCR signaling pathways are transmembrane proteins?

1. GPCR
2. G-protein
3. Effector protein (ex: adenylyl cyclase)
4. PKA

Answer 1

Ans1)C) intrinsic GTPase activity.

Explaination: Upon binding of the ligand (epinephrine) to the cytosolic face, a conformational change occurs to both the receptor and the G protein. The conformational change leads to the exchange of GDP for GTP on the α-subunit of the G protein.  Upon binding of GTP, the α-subunit dissociates and binds to its effector protein. The beta and gamma subunits facilitate the G-protein transfer and help specify the enzyme.After some random amount of time, the GTPase activity that is inbuilt into the α-subunit cleaves GTP to GDP. Cleavage of GTP causes the α-subunit to revert to its inactive conformation, to leave its target protein, and to re-associate with the β- and γ-subunits. The system thus returns to its resting state.

Ans-2)a)GPCR

Explaination: GPCR is a class of multipass (7 times) transmemembrane protein also called as seven-transmembrane receptor located in the cell membrane that binds extracellular substances and transmits signalsfrom these substances to an intracellular molecule called a Gprotein .