Answer: (B) At the exterior surface
Explanation:
G protein-linked receptors (GPLR) are also called G protein-coupled receptors, 7-Transmembrane receptors or heptahelical receptors. They conform a large protein family of receptors.
They helps to detect molecules (ligands) outside the cells. (At the exterior surface).
The LIGANDS that binds and activate these receptors include light-sensitive compounds (Opsins), odorants (olfactory receptors), pheromones (vomeronasal receptors which are situated near the vomer bone between the nose and the mouth), hormones and neurotransmitters (serotonin, dopamine, glutamate etc).
Let's take a bird's eye view at it.
° When a Ligand binds with a G protein-linked receptors (which occurs at the exterior surface), it undergoes a conformational change.
° As conformational change occurs, GPLR become active and interact with the G-proteins Heterotrimeric Subunits ( G-alpha, G-beta, G-gamma) in the plasma membrane (at the cytosol surface).
This step typically explains the ambiguity. i.e GPLRs receptors interacts with signaling ligands via the exterior surface but communication between GPLRs and G-proteins Heterotrimeric Subunits occurs in the cytosol membrane.
Hence, this Conformational Change then triggers the interaction between the GPLRs and a nearby G proteins.
I hope that helps!.
