RNA interference (RNAi) is a vital mechanism used by eukaryotic organisms to regulate gene expression. It involves the enzyme "dicer" cutting double-stranded RNA (dsRNA) into smaller fragments known as small interfering RNAs (siRNAs). These siRNAs then combine with the RNA-induced silencing complex (RISC) and target and degrade specific messenger RNAs (mRNAs).
Here's a breakdown of the process:
1. Formation of dsRNA: In certain situations, dsRNA is produced within the cell. This can occur naturally, such as during the replication of some viruses, or through experimental techniques in the laboratory.
2. Dicer enzyme: The enzyme dicer recognizes and binds to the dsRNA molecules. It then cleaves the dsRNA into smaller fragments, typically around 21-23 nucleotides in length. These fragments are the siRNAs.
3. Small interfering RNAs (siRNAs): The siRNAs are double-stranded RNA molecules with two distinct strands: the guide strand and the passenger strand. The guide strand is the one with a complementary sequence to the target mRNA, while the passenger strand is usually degraded.
4. RNA-induced silencing complex (RISC): The siRNAs associate with the RISC, forming a complex. The RISC consists of proteins that stabilize and guide the siRNA to the target mRNA.
5. Targeting mRNA: The guide strand within the RISC recognizes and binds to the complementary sequence on the target mRNA. This binding can occur at multiple sites along the mRNA molecule.
6. Degradation of mRNA: Once the RISC complex binds to the target mRNA, it triggers the degradation of the mRNA molecule. This prevents the mRNA from being translated into a protein.
By degrading specific mRNAs, RNA interference helps regulate gene expression by reducing the production of specific proteins. This mechanism plays a crucial role in various biological processes, including development, defense against viruses, and maintaining cellular homeostasis.
In summary, RNA interference is a mechanism in which dicer enzyme processes dsRNA into siRNAs. These siRNAs combine with the RISC complex and target and degrade specific mRNAs, thereby regulating gene expression in eukaryotic organisms.