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The bacterium that causes cholera, Vibrio cholerae, produces a toxin that alters a G-protein in intestinal cells. What effect does this toxin have?
AIt permanently blocks all chloride channels, preventing fluid loss
BIt converts the G-protein into an enzyme-linked receptor
CIt keeps a chloride channel active, causing large fluid loss from the body
DIt stops intestinal cells from making any G-proteins at all
Answer & Solution
Correct answer: C. It keeps a chloride channel active, causing large fluid loss from the body
1. The cholera toxin, choleragen, binds to cells lining the small intestine and enters those cells.
2. Inside the cell, it modifies a G-protein that controls the opening of a chloride channel.
3. This modification causes the channel to remain continuously active.
4. The continuously open channel results in large losses of fluids from the body and can cause fatal dehydration.
5. Blocking chloride channels entirely is the opposite effect from what the toxin actually causes.
6. The toxin modifies an existing G-protein rather than converting the receptor into a different receptor category.
7. The toxin does not stop G-protein production altogether; it modifies an existing G-protein's regulation of the channel.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 9 "Cell Communication", section 9.1 Signaling Molecules and Cellular Receptors_
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