Translation: chloramphenicol and the 50S subunit: 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.

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Biochemistry · Translation: chloramphenicol and the 50S subunit

Sample item

A premature neonate treated with chloramphenicol for sepsis develops abdominal distension, vomiting, ashen-grey colour and circulatory collapse. At the ribosomal level, which step of bacterial protein synthesis does this drug block?

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

The answer and the reasoning

C. Peptide bond formation by peptidyl transferase on the 50S subunit

Chloramphenicol binds the 50S subunit and inhibits peptidyl transferase activity of the 23S rRNA, so peptide bonds are not formed. Neonates, especially premature ones, have immature glucuronidation and cannot clear the drug, which accumulates and causes grey baby syndrome. Mitochondrial ribosomes resemble bacterial ones, which contributes to bone marrow toxicity.

Option by option

  • A. Translocation of peptidyl-tRNA by elongation factor G

    Macrolides block translocation on the 50S subunit; chloramphenicol acts on peptide bond formation itself.

  • B. Initiation complex formation with the 30S subunit and formylmethionyl-tRNA

    Aminoglycosides and related agents interfere with initiation at the 30S subunit.

  • C. Peptide bond formation by peptidyl transferase on the 50S subunit (correct)

    Inhibition of peptidyl transferase halts chain elongation.

  • D. Binding of aminoacyl-tRNA to the A site of the 30S subunit

    Tetracyclines block aminoacyl-tRNA binding at the A site of the 30S subunit.

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.

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Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is C, Peptide bond formation by peptidyl transferase on the 50S subunit. Chloramphenicol binds the 50S subunit and inhibits peptidyl transferase activity of the 23S rRNA, so peptide bonds are not formed.

Why is "Translocation of peptidyl-tRNA by elongation factor G" not the answer?

Macrolides block translocation on the 50S subunit; chloramphenicol acts on peptide bond formation itself.

Why is "Initiation complex formation with the 30S subunit and formylmethionyl…" not the answer?

Aminoglycosides and related agents interfere with initiation at the 30S subunit.

Why is "Binding of aminoacyl-tRNA to the A site of the 30S subunit" not the answer?

Tetracyclines block aminoacyl-tRNA binding at the A site of the 30S subunit.

What concept does this question test?

It tests Translation: chloramphenicol and the 50S subunit in Biochemistry. Neonates, especially premature ones, have immature glucuronidation and cannot clear the drug, which accumulates and causes grey baby syndrome. Mitochondrial ribosomes resemble bacterial ones, which contributes to bone marrow toxicity.

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: chloramphenicol and the 50S subunit?

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.