RNAi may be directed by small interfering RNAs (siRNAs) or microRNAs (miRNAs); how are these similar, and how are they different?

RNA interference is a biological process where small RNA molecules inhibit gene expression by neutralizing targeted mRNA molecules. It serves as a regulatory mechanism to control gene activity and defend against viral genomes. Both siRNAs and miRNAs function within this pathway to silence genes post-transcriptionally.

siRNAs are short, double-stranded RNA molecules typically derived from exogenous sources like viruses or experimental introduction. They guide the RNA-induced silencing complex (RISC) to perfectly complementary mRNA targets, leading to their cleavage and degradation, thus silencing specific genes.

miRNAs are endogenous, single-stranded RNA molecules processed from hairpin precursors within the cell. They usually bind imperfectly to target mRNAs, causing translational repression or destabilization rather than direct cleavage, allowing fine-tuned regulation of multiple genes simultaneously.