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GATE 2024 BT Q.38: solution and answer

GATE 2024 · BTQ.38 · 2 marks · MCQ

Match the enzyme (Column I) with its corresponding function (Column II).

Column I:
P. Primase
Q. Reverse transcriptase
R. RNA Replicase
S. DNA Polymerase III

Column II:
1. RNA dependent RNA synthesis
2. DNA dependent DNA synthesis
3. RNA dependent DNA synthesis
4. DNA dependent RNA synthesis

  1. (A)

    P-4; Q-1; R-3; S-2

  2. (B)

    P-2; Q-1; R-3; S-4

  3. (C)

    P-3; Q-4; R-2; S-1

  4. (D)

    P-4; Q-3; R-1; S-2

See the question in the paper
GATE 2024 BT question 38Tap to open full size

Answer and solution

ANSWER

Answer: D — P-4; Q-3; R-1; S-2 (Primase: DNA-dependent RNA synthesis; Reverse transcriptase: RNA-dependent DNA synthesis; RNA Replicase: RNA-dependent RNA synthesis; DNA Polymerase III: DNA-dependent DNA synthesis).

Official answer: DSource: Official answer key, GATE 2024 BT (IISc Bengaluru)

  1. P. Primase synthesizes a short RNA primer using a DNA template during DNA replication — template DNA, product RNA — this is DNA dependent RNA synthesis, matching function 4.

  2. Q. Reverse transcriptase (found in retroviruses) synthesizes DNA using an RNA genome as template — template RNA, product DNA — this is RNA dependent DNA synthesis, matching function 3.

  3. R. RNA Replicase (found in RNA viruses, e.g. Qβ phage) synthesizes new RNA strands using an RNA template — template RNA, product RNA — this is RNA dependent RNA synthesis, matching function 1.

  4. S. DNA Polymerase III is the main bacterial replicative polymerase, synthesizing DNA using a DNA template — template DNA, product DNA — this is DNA dependent DNA synthesis, matching function 2.

  5. Combining: P-4; Q-3; R-1; S-2.

  6. Compare with options: (A) P-4;Q-1;R-3;S-2 swaps Q and R — wrong. (B) P-2;Q-1;R-3;S-4 is entirely reversed — wrong. (C) P-3;Q-4;R-2;S-1 swaps P/S with Q/R — wrong. (D) P-4;Q-3;R-1;S-2 matches exactly — correct.

KEY IDEA

Classify each enzyme by its template (DNA or RNA) and its product (DNA or RNA): Primase = DNA-dependent RNA synthesis (RNA primer on a DNA template); Reverse transcriptase = RNA-dependent DNA synthesis (retroviral cDNA from an RNA genome); RNA Replicase = RNA-dependent RNA synthesis (RNA virus genome replication, e.g. Qβ phage); DNA Polymerase III = DNA-dependent DNA synthesis (the main bacterial replicative polymerase).

WATCH OUT FOR

Confusing reverse transcriptase with RNA replicase because both act on RNA — the distinguishing feature is the PRODUCT: reverse transcriptase's product is DNA (hence "RNA-dependent DNA synthesis"), while RNA replicase's product is RNA (hence "RNA-dependent RNA synthesis").

From the GATE 2024 BT paper. Every question of this paper · Download the full paper · All 21 Gene expression questions, with notes

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