MicroRNAs (miRNAs) silence gene expression post-transcriptionally. The mechanism involves:
- A miRNA binds the 5' cap of mRNA, blocking ribosome loading
- B miRNA forms dsRNA with mRNA, activating PKR and inducing interferon response
- C Mature miRNA binds RISC (RNA-induced silencing complex); imperfect complementarity with the 3' UTR of target mRNA causes translational repression and mRNA degradation ✓
- D miRNA directly methylates the promoter CpG islands of target genes, causing transcriptional silencing
Correct answer: C. Mature miRNA binds RISC (RNA-induced silencing complex); imperfect complementarity with the 3' UTR of target mRNA causes translational repression and mRNA degradation
Explanation
miRNA biogenesis: pri-miRNA → pre-miRNA (by Drosha/DGCR8) → cytoplasmic pre-miRNA → miRNA duplex (by Dicer) → mature single-stranded miRNA loaded into RISC (containing AGO2). Partial complementarity of miRNA seed sequence with 3' UTR recruits CCR4-NOT deadenylase complex causing mRNA deadenylation, decapping, and degradation, or translational repression. Perfect complementarity (as in siRNA) causes direct AGO2-mediated mRNA cleavage. Dysregulation of miRNAs is a common mechanism in cancer.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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