What is important to remember about G-Protein coupled receptors?

• A. They are ligand-gated ion channels
• B. They are intracellular receptors
• C. They convey information to effector proteins
• D. They are cytosolic enzymes that catalyze reactions

Answer: (C)

GPCRs relay signals from outside to inside by activating G proteins, which then regulate downstream effector proteins to propagate the message.

When a ligand binds, the receptor activates a heterotrimeric G protein on the inside of the membrane. The G protein then modulates effector enzymes such as adenylyl cyclase or phospholipase C (and can influence ion channels), generating second messengers like cAMP or IP3/DAG that carry the signal onward inside the cell. This makes the primary role of GPCRs to convey information to effector proteins, rather than forming pores or acting as enzymes themselves.

They are not ligand-gated ion channels (that would be a direct pore that opens in response to ligand), nor intracellular receptors (which bind ligands inside the cell), nor cytosolic enzymes that catalyze reactions. GPCRs are membrane-bound, seven-transmembrane receptors whose main function is to initiate these signaling cascades via G proteins.