How RNA Interference (RNAi Silencing) Works
Cells can inhibit the expression of individual genes (stop proteins from being made) by interfering with a mRNA being transcribed.
This is done vai a small double-stranded RNA.   An enzyme named DICER snips short interfering RNAs (siRNA) from longer double
stranded RNAs made by (A) self-copying gene sequences,  (B) by replicating viruses, or (C) regulatory RNA sequences known as
microRNAs.   All the RNAs (A, B, & C) are cleaved by DICER enzyme into short siRNA pieces that can suppress gene expression. 
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 How RNA Interference (RNAi Silencing) Works

The short siRNA pieces (A, B, & C above) unwind into single strand RNAs, which then combine with proteins to form a
complex called RISC [RNA-Induced Silencing Complex].  The RISC then captures a native mRNA molecule that complements
the short siRNA sequence.  If the pairing  [native mRNA and siRNA piece]  is essentially perfect, the native mRNA is cut into
useless RNA fragments that aren't translated.  If however, the pairing is less than perfect then the RISC complex binds to the
mRNA and blocks ribosome movement along the native mRNA also halting translation. The net effect is NO PROTEIN IS MADE.

A fluorescent protein gene was incorporated into cultured cells and their glow revealed successful translation of their mRNA into lamin protein. However, the lamin protein glow
disappeared in cells that took up an
artificial siRNA for the lamin gene.