# DBT JRF 2020 — Question 134

Exam: DBT JRF 2020 · Section: B · Topic: Biotechnology · Difficulty: Easy

## Question

Small/short interfering RNA (siRNA) is a commonly used RNA tool that causes

## Options

- **A.** permanent silencing of protein coding genes
- **B.** deletion of protein encoding genes
- **C.** short-term silencing of protein coding genes
- **D.** duplication of protein encoding genes

## Answer

Option C

## Explanation

siRNA (small/short interfering RNA): typically 21–23 nucleotide dsRNA molecules (with 2-nt 3' overhangs) that mediate RNA interference (RNAi). Mechanism: siRNA → loaded into RISC (RNA-Induced Silencing Complex) → Argonaute-2 (Ago2) slicer activity; guide strand directs RISC to complementary mRNA → mRNA cleaved at position 10/11 from 5' end of guide strand → mRNA degraded. The silencing is TRANSIENT (temporary) because: (1) siRNA molecules do not replicate and are diluted by cell division; (2) siRNA is degraded by cellular nucleases; (3) siRNA does NOT integrate into the genome or modify the gene sequence. For stable/permanent silencing, shRNA (short hairpin RNA expressed from a vector) or CRISPR-Cas9 genome editing is used. siRNA is widely used for gene function studies and has therapeutic applications (e.g. inclisiran for hypercholesterolaemia).

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