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GATE 2019 BT Q.3: solution and answer

GATE 2019 · BTQ.3 · 1 mark · MCQ

Tetracycline inhibits the

  1. (A)

    interaction between tRNA and mRNA

  2. (B)

    translocation of mRNA through ribosome

  3. (C)

    peptidyl transferase activity

  4. (D)

    binding of amino-acyl tRNA to ribosome

See the question in the paper
GATE 2019 BT question 3Tap to open full size

Answer and solution

ANSWER

D — binding of amino-acyl tRNA to ribosome

Official answer: DSource: Official answer key, GATE 2019 BT (IIT Madras)

  1. Tetracycline is a well-known bacterial translation inhibitor that binds the 30S ribosomal subunit.

  2. Its specific mechanism is steric blockage of the A site on the 30S subunit, which prevents the aminoacyl-tRNA-EF-Tu-GTP ternary complex from docking there.

  3. Option A (interaction/pairing between tRNA and mRNA) is not tetracycline's target — codon-anticodon pairing proceeds once a tRNA is positioned; this is not tetracycline's described mechanism.

  4. Option B (translocation of mRNA/tRNA through the ribosome) is the EF-G-dependent step, blocked by drugs such as fusidic acid, not tetracycline.

  5. Option C (peptidyl transferase activity, the 50S ribozyme reaction) is inhibited by chloramphenicol, not tetracycline.

  6. Option D (binding of amino-acyl tRNA to the ribosome) matches tetracycline's textbook mechanism exactly — it blocks the A site so aminoacyl-tRNA cannot bind.

  7. Therefore the correct answer is D.

KEY IDEA

Tetracycline is a bacteriostatic protein-synthesis inhibitor that binds the 30S ribosomal subunit and sterically blocks the A site, preventing the aminoacyl-tRNA-EF-Tu-GTP ternary complex from docking — it stops aminoacyl-tRNA from binding to the ribosome.

WATCH OUT FOR

Confusing tetracycline (blocks aminoacyl-tRNA binding at the A site) with chloramphenicol (blocks peptidyl transferase) or fusidic acid (blocks translocation/EF-G recycling).

From the GATE 2019 BT paper. Every question of this paper · Download the full paper · All 21 Gene expression questions, with notes

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