Question

70. Cholera is an intestinal, diarrheal disease that often results in death due to severe fluid loss. Symptoms are due to the presence of a bacterial toxin, which alters the normal transport of chloride ions across the cell membrane (below) and ultimately leads to water loss from cells in the small intestine. You and a partner are asked to explain how the cholera toxin could cause fluid loss. Your partner gives the following explanation: “I think the cholera toxin binds to the chloride transport protein, resulting in more chloride ions being pumped out of the cell. With more chloride ions outside of the cell, water will flow down the concentration gradient and out of the cell.”

Which of the following is another plausible explanation?

a. Cholera toxin alters the chloride transport protein causing chloride ions to flow quickly into the cell, which pushes the water out of the cell.

b. Cholera toxin makes the lipid bilayer more rigid, which means water builds up outside of the cell as it is unable to pass through the membrane

c. Cholera toxin acts of a different cellular protein, causing it to produce a molecule that then activates transport of chloride ions through the membrane

d. Cholera toxin binds to the chloride transport protein, preventing the transport of chloride ions across the membrane.

Answer 1

Answer-

According to the given question- Cholera are marked by diarrhea and is caused by bacterium vibrio cholerae due to ingestion of contaminated food and water.

• In intestinal lumen the vibrio cholerae attaches to the surface of the cell and the microorganisms secrete Cholera toxin made up of two subunits one is A subunit is catalytic domain which is made up of 2 chain  and second is B subunit is binding domain, made up of five chains binds with the receptors of host cell.
• B sbunit binds with the glycoprotein GM1 ganglioside. A subunit made up of two domain A1 has toxin activity and A2 domain attaches with B subunit and both A1 and A2 are linked by disulfide bonds. binding of Cholera toxin to GM1 ganglioside receptors triggers transport to the endoplasmic reticulum where A1 is released which moved to the cytoplasm which modify the characteristice of G protein which bind with the enzyme adenyl cyclase and responsible for controlling its activity.
• Inactive G protein made up of alpha, beta and gamma subunit and carries a GDP molecule. when a hormone activates the G protein which causes release of GDP and take GTP that leads to separation of alpha subunit from beta and gamma subunit .
• alpha subunit has ATPase activity. activated alpha subunit binds with the adenyl cyclase and activated it which convert ATP to cyclic adenosine monophosphate (cAMP) . after activation the alpha subunit form GDP and inactivate itself as well as adenyl cyclase.
• A1 chain of Cholera toxin is also a enzyme which uses NAD⁺ which consist of nicotenamide, ribose sugar and an ADP molecule which add ADP ribose to alpha subunit of G protein which prevent cleaving of GTP into GDP that causes the adenyl cyclase remains activated continuously for longer period of time causing increase level of cAMP . the high level of cAMP causes enzyme protein kinase A activation which also responsible for activating CFTR ot cystic fibrosis transmembrane conductance regulator which is responsible for exporting chloride ion. this causes export of chloride ion outside the cells due to which the water molecule also diffuses to maintain osmolarity causes intestinal lumen have more water and ions causing diarrhea.

So according to the above information the correcy answer for the question is (C) Cholera toxin acts of a different cellular protein, causing it to produce a molecule that then activates transport of chloride ions through the membrane