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GATE 2023 BT Q.11: solution and answer

GATE 2023 · BTQ.11 · 1 mark · MCQ

Eukaryotic transcription is carried out by

  1. (A)

    DNA-dependent RNA polymerase

  2. (B)

    DNA-dependent DNA polymerase

  3. (C)

    RNA-dependent DNA polymerase

  4. (D)

    RNA-dependent RNA polymerase

See the question in the paper
GATE 2023 BT question 11Tap to open full size

Answer and solution

ANSWER

Eukaryotic transcription is carried out by DNA-dependent RNA polymerase.

Official answer: ASource: Official answer key, GATE 2023 BT (IIT Kanpur)

  1. Transcription is defined as the synthesis of RNA using a DNA template — so the correct answer must describe an enzyme with DNA as template and RNA as product.

  2. (A) DNA-dependent RNA polymerase: template = DNA, product = RNA — exactly matches transcription. In eukaryotes this activity is carried out by RNA polymerases I, II and III. Correct.

  3. (B) DNA-dependent DNA polymerase: template = DNA, product = DNA — this is DNA replication, not transcription. Incorrect.

  4. (C) RNA-dependent DNA polymerase: template = RNA, product = DNA — this is reverse transcriptase, used by retroviruses, not by eukaryotic cells for normal transcription. Incorrect.

  5. (D) RNA-dependent RNA polymerase: template = RNA, product = RNA — used by RNA viruses to replicate their genomes, not used in eukaryotic transcription. Incorrect.

  6. Hence eukaryotic transcription is carried out by DNA-dependent RNA polymerase, option (A).

KEY IDEA

Transcription is the DNA-templated synthesis of RNA; in eukaryotes this is carried out by DNA-dependent RNA polymerases (RNA Pol I, II and III), each transcribing a distinct class of genes (rRNA, mRNA/most genes, tRNA/5S rRNA respectively).

WATCH OUT FOR

Confusing the four polymerase/enzyme classes by template-versus-product: DNA-dependent DNA polymerase (B) performs replication, not transcription; RNA-dependent DNA polymerase (C) is reverse transcriptase, used by retroviruses to convert their RNA genome into DNA; RNA-dependent RNA polymerase (D) is used by RNA viruses to replicate RNA genomes — none of these describe normal eukaryotic transcription.

From the GATE 2023 BT paper. Every question of this paper · Download the full paper · All 21 Gene expression questions, with notes

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