Which of the following situations is most similar to extracellular binding to a GPCR?

(A) A police officer pulling over a speeding car on the expressway

(B) A celebrity chef visiting the kitchen of another restaurant

(C) A driver giving their order to a person through a drive-up window

(D) A taxi driver picking up a group of passengers

G-protein coupled receptors (GPCRs) are a common type of protein receptor containing seven transmembrane segments and bearing intracellular and extracellular portions. The structure of a typical GPCR and its associated partners is shown below. GPCRs are coupled to G-proteins consisting of three subunits (a, β, and γ) that bind the nucleotides GTP or GDP on the intracellular side of the GPCR. The presence or absence of a ligand on the extracellular side of the GPCR determines whether GDP or GTP will bind to the intracellular G-protein. Extracellular ligand binding initiates GDP being exchanged for GTP and the separation of the G-protein. One subunit will travel to join with a secondary partner and will initiate a cascade of signaling effects within the cell. In the example shown below, the secondary partner is adenylyl cyclase and the signaling is cAMP upregulation.

Transcribed Image Text:

JAMAM ooooo -Ligand (epinephrine) G-protein-linked receptor α GTP EXTRACELLULAR oooooo nos ma βγ GDP INTRACELLULAR LO V V W X V W X Y WV V α ALLAHLAOK GTP enzyme enzyme-PO α GTP CAMP MAMAX wy oooooo Adenylyl Cyclase ATP CAMP-dPK