Q. Consider the following statements regarding the initiation of RNAi:
1.RNA interference is a natural cellular process used to regulate gene expression and provide defense against viral infections.
2.The process is typically triggered by the presence of single-stranded RNA (ssRNA) in the cytoplasm.
3.An enzyme called Dicer is responsible for cutting long double-stranded RNA into shorter fragments known as siRNA.
Which of the statements given above are correct?

[A] 1 and 2 only

[B] 1 and 3 only

[C] 2 and 3 only

[D] 1, 2 and 3

Answer: B
Notes:

Explanation:

  • Statements 1 and 3 are correct. RNA interference (RNAi) is a conserved cellular mechanism for regulating gene expression and defending against viruses by degrading specific messenger RNA (mRNA) molecules. The process involves the enzyme Dicer, a ribonuclease III-type enzyme, which cleaves long double-stranded RNA (dsRNA) into short interfering RNA (siRNA) fragments, typically 21–23 base pairs long.
  • Statement 2 is incorrect: RNAi is triggered by double-stranded RNA (dsRNA). Single-stranded RNA is the normal state for mRNA and does not trigger this defense/regulation mechanism.
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