Answer :
The enzyme that is used to cut double stranded RNA molecules into 21 nucleotide base pair (bp) RNA molecules with sequences complementary to mRNA is 'dicer.'
Dicer is an important enzyme in the RNA interference (RNAi) pathway. It belongs to a class of ribonuclease enzymes that can cleave double-stranded RNA (dsRNA) and pre-microRNA (pre-miRNA) into small interfering RNA (siRNA). These siRNA molecules are typically around 21-25 nucleotides long and can guide the degradation or translation inhibition of complementary mRNA molecules, effectively regulating gene expression.
Here's a simple step-by-step explanation of how dicer works:
Recognition: Dicer recognizes and binds to double-stranded RNA (dsRNA) molecules. These dsRNA can either be viral or stem-loop structures of pre-miRNA in cells.
Cleavage: Dicer enzymatically cleaves the dsRNA into short double-stranded fragments of about 21-25 base pairs in length, with 2-nucleotide overhangs at the 3' ends.
Incorporation into RISC: The resulting small interfering RNAs (siRNAs) are then incorporated into the RNA-induced silencing complex (RISC).
Targeting: RISC uses the siRNA as a guide to find and bind complementary mRNA molecules.
Gene Silencing: Once bound, RISC mediates mRNA degradation or translation repression, effectively silencing the expression of that gene.
This process of gene silencing by RNAi is crucial for regulating gene expression, maintaining genomic stability by silencing harmful transposable elements, and defending against viruses in cells.
Therefore, the correct choice is 'dicer' - it serves a pivotal role in the creation of small RNA fragments from double-stranded RNA, facilitating the RNA-induced gene-silencing pathway.
