Apentix/AP Biology/Unit 4: Cell Communication and Cell Cycle/Question

AP Biologymediummcq1 pt

How does a G-protein-coupled receptor start its cascade?

A.Ligand binding activates the G protein to exchange GDP for GTP

B.The G protein directly phosphorylates DNA

C.The receptor opens a calcium channel permanently

D.Ligand binding deactivates the receptor

Explanation

Core Concept

The receptor changes shape, the G protein swaps GDP for GTP, and its subunits then activate downstream enzymes like adenylyl cyclase. GTP hydrolysis resets the switch.

Correct Answer

ALigand binding activates the G protein to exchange GDP for GTP

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