A researcher adds a non-hydrolyzable GTP analogue to a cell-free system containing G proteins. Which downstream signaling event will be most directly affected?

• A The Gα subunit remains permanently inactive
• B Adenylyl cyclase is persistently inhibited
• C Phospholipase C is irreversibly activated by the βγ subunit
• D The Gα subunit remains in a constitutively active state ✓

Explanation

G proteins are activated when GTP binds to the α subunit, causing dissociation from βγ and activation of effectors. The intrinsic GTPase activity of Gα hydrolyzes GTP to GDP, returning the protein to its inactive state. A non-hydrolyzable analogue (e.g., GTPγS) locks Gα in the GTP-bound active conformation, producing persistent signaling. This is the principle exploited by cholera toxin, which ADP-ribosylates Gsα and inhibits its GTPase.

Reference: Lehninger Principles of Biochemistry, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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