Unit 6B Cholera CFTR

Question 1

How does cholera toxin cause diarrhea?
a) Stimulates water reabsorption
b) Blocks sodium channels
c) Activates CFTR by increasing cAMP
d) Inhibits protein digestion

Answer 1

c) Activates CFTR by increasing cAMP

Explanation: Cholera toxin modifies a G protein, causing persistent activation of adenylyl cyclase → ↑ cAMP → sustained CFTR activation → Cl− and water secretion into the gut.

Question 2

Which second messenger is elevated by cholera toxin?
a) cAMP
b) IP3
c) DAG
d) cGMP

Answer 2

a) cAMP

Explanation: Cholera toxin prevents inactivation of the Gα subunit, keeping adenylyl cyclase active and raising intracellular cAMP levels.

Question 3

What does the CFTR channel normally transport?
a) Na+ into cells
b) Cl− out of cells
c) H+ into the lumen
d) Glucose into the blood

Answer 3

b) Cl− out of cells

Explanation: CFTR is a chloride channel on the apical membrane; its activity draws water into the lumen when active.

Question 4

What is the proposed evolutionary link between CFTR and cholera?
a) CFTR evolved from cholera toxin
b) CFTR mutation prevents infection
c) CF mutations block glucose absorption
d) CF carriers may survive cholera better

Answer 4

d) CF carriers may survive cholera better

Explanation: Heterozygotes with reduced CFTR function may secrete less Cl− during infection, helping them retain water and survive better in cholera outbreaks.

Question 5

What is the trafficking pathway of cholera toxin inside cells?
a) ER → Golgi → nucleus
b) Cell surface → lysosome
c) Endocytosis → Golgi → ER → cytosol
d) Mitochondria → ER → exocytosis

Answer 5

c) Endocytosis → Golgi → ER → cytosol

Explanation: Cholera toxin hijacks the retrograde transport pathway to reach the ER, then enters the cytosol where it modifies G proteins.