Question

the extracellular environment.

adapted from raufman, j. r (1998). cholera. am. j. med. 104, 386-394.

based on the information above, which of the following correctly describes cholera toxin and its effect on intestinal epithelial cells?

choose 1 answer:

a cholera toxin is an extracellular signal that decreases adenylyl cyclase activity.

b cholera toxin is an intracellular signal that increases extracellular chloride ion concentration.

c cholera toxin is an intracellular signal that decreases intracellular camp concentration.

d cholera toxin is an extracellular signal that increases the dephosphorylation of protein kinase a.

Explanation:

• Option A: Cholera toxin actually increases adenylyl cyclase activity, so A is wrong.
• Option B: Cholera toxin is an extracellular signal (binds to cell surface receptors), not intracellular, so B is wrong.
• Option C: Cholera toxin increases intracellular cAMP concentration (by activating adenylyl cyclase), so C is wrong.
• Option D: Cholera toxin is an extracellular signal. It increases cAMP, which activates protein kinase A, and the increased cAMP can lead to increased dephosphorylation - related processes or the activation state of protein kinase A's targets, and the description about it being an extracellular signal and its effect on protein kinase A dephosphorylation - related processes (in the context of its mechanism) makes D the correct choice.

Answer:

D. Cholera toxin is an extracellular signal that increases the dephosphorylation of protein kinase A.