Translation: diphtheria toxin: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

Biochemistry · Translation: diphtheria toxin

Sample item

A 6-year-old unvaccinated child has fever, a grey adherent tonsillar pseudomembrane, bull neck and myocarditis. The toxin responsible acts by inactivating which target?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Eukaryotic elongation factor 2, by ADP-ribosylation of diphthamide

Diphtheria toxin catalyses the transfer of ADP-ribose from NAD+ to diphthamide, a modified histidine on eEF-2, so ribosomal translocation stops and protein synthesis ceases, causing cell death in the pharynx, heart and nerves. Cholera toxin modifies Gs, pertussis toxin modifies Gi, and Shiga toxin and ricin depurinate 28S rRNA.

Option by option

  • A. Gi alpha subunit, by ADP-ribosylation

    Gi modification is the action of pertussis toxin.

  • B. Gs alpha subunit, by ADP-ribosylation

    Gs alpha modification is the action of cholera toxin and causes secretory diarrhoea.

  • C. Eukaryotic elongation factor 2, by ADP-ribosylation of diphthamide (correct)

    ADP-ribosylation of eEF-2 halts ribosomal translocation, which is the lethal action of diphtheria toxin.

  • D. 28S ribosomal RNA, by removing an adenine base

    Depurination of 28S rRNA is the action of Shiga toxin and ricin.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Eukaryotic elongation factor 2, by ADP-ribosylation of diphthamide. Diphtheria toxin catalyses the transfer of ADP-ribose from NAD+ to diphthamide, a modified histidine on eEF-2, so ribosomal translocation stops and protein synthesis ceases, causing cell death in the pharynx, heart and nerves.

Why is "Gi alpha subunit, by ADP-ribosylation" not the answer?

Gi modification is the action of pertussis toxin.

Why is "Gs alpha subunit, by ADP-ribosylation" not the answer?

Gs alpha modification is the action of cholera toxin and causes secretory diarrhoea.

Why is "28S ribosomal RNA, by removing an adenine base" not the answer?

Depurination of 28S rRNA is the action of Shiga toxin and ricin.

What concept does this question test?

It tests Translation: diphtheria toxin in Biochemistry. Cholera toxin modifies Gs, pertussis toxin modifies Gi, and Shiga toxin and ricin depurinate 28S rRNA.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Translation: diphtheria toxin?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.