Translation: aminoacyl-tRNA synthetase: 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: aminoacyl-tRNA synthetase

Sample item

An enzyme sometimes activates a similar smaller amino acid (valine instead of isoleucine) but then hydrolyses the wrong product at a separate editing site before it ever reaches the ribosome. Which enzyme proofreads in this way?

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

The answer and the reasoning

D. Aminoacyl-tRNA synthetase

The ribosome decodes only the codon-anticodon pairing and cannot check the amino acid, so accuracy depends on the charging enzyme. Many have a second editing site that hydrolyses misactivated or mischarged products. This gives overall error rates of roughly one per ten thousand amino acids.

Option by option

  • A. Peptidyl transferase

    Peptidyl transferase forms peptide bonds and does not check which amino acid is attached.

  • B. Peptidyl-tRNA hydrolase

    Peptidyl-tRNA hydrolase salvages abortive peptidyl transfer RNAs and does not edit amino acid charging.

  • C. Elongation factor Tu

    Elongation factor Tu delivers transfer RNAs, and checks codon pairing rather than amino acid identity.

  • D. Aminoacyl-tRNA synthetase (correct)

    Correct. Its editing site hydrolyses misactivated or mischarged amino acids before translation.

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 D, Aminoacyl-tRNA synthetase. The ribosome decodes only the codon-anticodon pairing and cannot check the amino acid, so accuracy depends on the charging enzyme.

Why is "Peptidyl transferase" not the answer?

Peptidyl transferase forms peptide bonds and does not check which amino acid is attached.

Why is "Peptidyl-tRNA hydrolase" not the answer?

Peptidyl-tRNA hydrolase salvages abortive peptidyl transfer RNAs and does not edit amino acid charging.

Why is "Elongation factor Tu" not the answer?

Elongation factor Tu delivers transfer RNAs, and checks codon pairing rather than amino acid identity.

What concept does this question test?

It tests Translation: aminoacyl-tRNA synthetase in Biochemistry. Many have a second editing site that hydrolyses misactivated or mischarged products. This gives overall error rates of roughly one per ten thousand amino acids.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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: aminoacyl-tRNA synthetase?

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.