Q.27 The cellular process which utilizes RNA-induced silencing complex to block
gene expression is
(A) RNA editing
(B) RNA interference
(C) RNA polyadenylation
(D) RNA splicing

RNA interference (RNAi) is the cellular process that utilizes the RNA-induced silencing complex (RISC) to block gene expression. This mechanism silences specific genes post-transcriptionally by degrading target mRNA or inhibiting translation.​

Correct Answer

(B) RNA interference

RNA interference employs small interfering RNAs (siRNAs) or microRNAs (miRNAs) that integrate into RISC, a multiprotein complex containing Argonaute proteins. RISC uses the guide RNA strand to recognize complementary mRNA sequences, leading to cleavage or translational repression, thus blocking gene expression.​

Option Explanations

RNA Editing (A)

RNA editing alters specific nucleotides in RNA transcripts post-transcription, such as C-to-U or A-to-I deamination, or U insertion/deletion in organelles like mitochondria. It diversifies proteins from a single gene but does not involve RISC or gene silencing.​

RNA Interference (B)

This correct process triggers gene silencing via double-stranded RNA processed by Dicer into siRNAs, which load into RISC. RISC then targets and degrades mRNA or blocks its translation, regulating gene expression in eukaryotes.​

RNA Polyadenylation (C)

Polyadenylation adds a poly(A) tail to mRNA’s 3′ end during processing, enhancing stability, export, and translation efficiency. It stabilizes transcripts rather than blocking expression and lacks RISC involvement.​

RNA Splicing (D)

Splicing removes introns and joins exons in pre-mRNA via the spliceosome, producing mature mRNA. This maturation step enables proper translation but does not silence genes or use RISC.