[Campbell Biology P.273] Vibrio cholerae produces a toxin that locks the G protein in its ac... | Practice Question

Vibrio cholerae produces a toxin that locks the G protein in its active state, rendering it unable to hydrolyze GTP to GDP. Based on Figure 11.12 and the associated text, which of the following is the most direct consequence of this toxin's action?

  • A: Continuous activation of adenylyl cyclase, leading to high cAMP levels.
  • B: Blockage of the first messenger binding to the GPCR.
  • C: Inhibition of protein kinase A, preventing cellular responses.
  • D: Decreased conversion of ATP to cAMP.

Explanation

The cholera toxin locks the G protein in its active, GTP-bound state because it cannot hydrolyze GTP to GDP. This continuously stimulates adenylyl cyclase, leading to abnormally high levels of cAMP in the cell. High cAMP then activates protein kinase A, triggering excessive cellular responses, such as the secretion of salts and water in intestinal cells, causing severe diarrhea.