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GATE 2025 BT Q.16: solution and answer

GATE 2025 · BTQ.16 · 1 mark · MCQ

Which one of the following is true for piRNAs?

  1. (A)

    piRNAs silence transposable elements in germ cells

  2. (B)

    piRNA is the abbreviation of P-element interacting RNA

  3. (C)

    piRNAs modify the 2'-OH of ribose with methyl group

  4. (D)

    piRNA is a long non-coding RNA

See the question in the paper
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Answer and solution

ANSWER

The correct answer is (A): piRNAs silence transposable elements in germ cells.

Official answer: ASource: Official answer key, GATE 2025 BT (IIT Roorkee)

  1. piRNAs (Piwi-interacting RNAs) are small non-coding RNAs of about 24-31 nucleotides, found predominantly in animal germline cells.

  2. Option (A): piRNAs bind Piwi-clade Argonaute proteins and direct silencing of transposable elements in germ cells, protecting genome integrity during gametogenesis — this is the defining, well-established function of piRNAs. TRUE.

  3. Option (B): The 'pi' in piRNA stands for Piwi-interacting, not 'P-element interacting.' P-elements are a specific class of DNA transposon (notably in Drosophila) that piRNAs can help silence, but this is not the origin of the name. FALSE.

  4. Option (C): piRNAs themselves carry a 2'-O-methyl modification on the ribose of their 3' terminal nucleotide, added post-biogenesis by the methyltransferase Hen1 (Pimet in Drosophila) — i.e., piRNAs are the substrate that gets methylated, not the agent performing methylation on something else. The statement reverses this relationship. FALSE.

  5. Option (D): piRNAs are small non-coding RNAs (~24-31 nt), a class distinct from long non-coding RNAs (lncRNAs, typically >200 nt). FALSE.

  6. By elimination and direct knowledge of piRNA biology, only (A) is true.

KEY IDEA

piRNAs (Piwi-interacting RNAs) are small non-coding RNAs (~24-31 nt) found chiefly in germline cells, where they associate with Piwi-clade Argonaute proteins to silence transposable elements and protect genome integrity during gametogenesis.

WATCH OUT FOR

Confusing the "pi" in piRNA (Piwi-interacting) with "P-element interacting," or confusing which molecule methylates which — piRNAs themselves are 2'-O-methylated at their 3' end by the methyltransferase Hen1, they are not agents that methylate other molecules.

From the GATE 2025 BT paper. Every question of this paper · Download the full paper · All 21 Gene expression questions, with notes

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