Cholera toxin (USMLERx question)

[dyspareunia]

The question gives you a presentation of someone with cholera and asks you about the toxin.

A. An A-B heat labile toxin that permanently activates adenyl cyclase to increase cAMP
B. An A-B toxin that activates adenyl cyclase by ADP ribosylation to increase cAMP


Is it really necessary to know the toxin in this much detail to differentiate between the above two answers (both were provided as answers to this question)?

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[Brain Bucket]

Toxin (A of the A-B) was tested in a roundabout way on my Micro shelf. Make of that what you will.

 

[Enzymes]

The question gives you a presentation of someone with cholera and asks you about the toxin.

A. An A-B heat labile toxin that permanently activates adenyl cyclase to increase cAMP
B. An A-B toxin that activates adenyl cyclase by ADP ribosylation to increase cAMP


Is it really necessary to know the toxin in this much detail to differentiate between the above two answers (both were provided as answers to this question)?

Yes, I am pretty sure you should know the toxins well (i.e. their specific mechanisms).

 

[notbobtrustme]

that's not too much detail, that's very high yield in fact. Similar mechanism questions come up all the time.

 

[evilboy]

This mechanism is common in a few toxins. ADP ribosylation mechanism is useful to know and solidifies Biochem concepts as well.

 

[dyspareunia]

Yes, I am pretty sure you should know the toxins well (i.e. their specific mechanisms).

that's not too much detail, that's very high yield in fact. Similar mechanism questions come up all the time.

I understand that we should know the toxins, but what's the difference between answer A and answer B? Only one of them is correct.

Cholera toxin is heat-labile, acts via ADP-ribosylation, and permanently activates adenylate cyclase. In other words, it fulfills everything in both of those answers even though only one of the answers is correct.

 

[evilboy]

Its B because it uses a buzz word.

 

[dyspareunia]

Also Rx says "Bottom line is v.cholerae causes a secretory diarrhea by permanently activating Gs".

No mention of ADP ribosylation (though obviously it is the mechanism).

 

[evilboy]

Also Rx says "Bottom line is v.cholerae causes a secretory diarrhea by permanently activating Gs".

No mention of ADP ribosylation (though obviously it is the mechanism).

Oh God, I confused it with Diptheria, I'm sorry dys. Page 126 of FA 2014. Wiki says its an ADP ribosylator but I will defer my responses to someone who is better equipped to answer, I'm sorry again.

 

[Enzymes]

Now that I take a closer look, I see what you mean. What the heck is the answer? Both seem right, but I would have chosen A since First Aid seems to indicate that.

 

[syma]

I would have gone with B.

ADP ribosylation

 

[syma]

It doesn't permanently activate adenyl cyclase directly, as the first choice implies. It permanently activates the alpha subunit by ADP ribosylation.

The main effect (afaik) is that it is not switched off because cholera prevents the deactivation of the alpha sub unit of the G protein

 

[notbobtrustme]

Its B because it uses a buzz word.

B is mos def not a buzzword, it's simply the way it works.

A has the buzzword "heat labile"

 

[ScarletKnights]

A mentions heat labile which is involved with ETEC. ETEC has a heat labile and a heat stabile toxin.

 

[dyspareunia]

B is the correct answer.

It doesn't permanently activate adenyl cyclase directly, as the first choice implies. It permanently activates the alpha subunit by ADP ribosylation.

The main effect (afaik) is that it is not switched off because cholera prevents the deactivation of the alpha sub unit of the G protein

I don't see how the first answer implies "direct" activation, but the second answer doesn't. Based on the answer explanations, they want you to think of answer A as ETEC (which works exactly the same as cholera). It's likely "B" because FA doesn't say anything about cholera toxin being heat-labile.. even though it is.