What is the role of the enzyme Dicer in gene silencing?

• A. It produces long double-stranded RNA from siRNA
• B. It converts single-stranded RNA to double-stranded RNA
• C. It processes long double-stranded RNA into siRNA
• D. It enhances gene expression

Answer: (C)

Dicer plays a crucial role in the RNA interference (RNAi) pathway, which is essential for gene silencing. The enzyme is responsible for processing long double-stranded RNA (dsRNA) molecules into small interfering RNA (siRNA). The siRNA molecules generated by Dicer typically consist of 21-23 nucleotides in length and have two overhanging nucleotides at their 3' ends.

Upon the introduction of long dsRNA into a cell, Dicer recognizes and cleaves it into these smaller siRNA fragments. This processing step is critical because the siRNA then guides the RNA-induced silencing complex (RISC) to complementary messenger RNA (mRNA) targets, leading to mRNA degradation or repression of translation, ultimately silencing the expression of specific genes.

This function of Dicer is a key part of the cellular machinery that regulates gene expression and protects the cell from viral RNA and transposons, making it fundamental to the gene silencing process. The other options do not accurately reflect the specific role of Dicer in the RNAi mechanism.