Which of the following is an example of an effector in GPCR signaling?

• A. DNA polymerase
• B. Lysosome
• C. Adenylyl Cyclase
• D. Ribosome

Answer: (C)

In GPCR signaling, the signal from the receptor is transmitted by an effector that changes the cell’s biochemistry and generates second messengers. After a GPCR activates a G protein, the G protein then interacts with an effector to produce these messengers. Adenylyl cyclase is the classic GPCR effector: when stimulated by the Gs subunit, it converts ATP to cyclic AMP, a second messenger that activates protein kinase A and triggers a cascade of cellular responses. If Gi is involved, it can inhibit adenylyl cyclase, reducing cAMP levels and dampening the response. The other options aren’t the targets that generate second messengers in GPCR signaling—DNA polymerase, lysosome, and ribosome are not components that mediate this signaling pathway.