The cholera bacterium Vibrio cholerae produces an enzyme toxin that chemically modifies a G protein involved in regulating salt and water secretion in intestinal cells. Stuck in its active form, the modified G protein stimulates the production of a high concentration of cAMP, which causes the intestinal cells to secrete large amounts of salts into the intestines, with water following by osmosis. An infected person quickly develops profuse diarrhea and if left untreated can soon die from the loss of water and salts.

What is the basic effect of the cholera toxin?

A. The basic effect of the cholera toxin is loss of specificity of the response of intestinal cells to a

B. The basic effect of the cholera toxin is premature termination of a signaling pathway.

C. The basic effect of the cholera toxin is signal amplification.

C. The basic effect of the cholera toxin is signal amplification.

Explanation:

Cholera toxin can cause its symptoms by amplifying the signals responsible for intestinal electrolyte transport through the following process:

The toxin binds to a membrane ganglioside (a phospholipid with carbohydrate residues) in the secretory cells in the small intestine. After that, a toxin subunit penetrates the cell, causing permanent activation of a G protein.

G protein activates adenylate cyclase, which catalyzes the formation of cAMP (A type of secondary messenger, important in signal transduction in cells), responsible for activating protein kinases.

Proteins undergo phosphorylation, this process amplifies chloride ions (Cl⁻) secretion.

The flow of negatively charged chloride ions out of the cell causes positively charged sodium ions to follow them in the flow.

Then water follows the electrolytes to the lumen of the small intestine by osmosis, resulting in severe diarrhea.