Final answer:
RNA interference (RNAi) is a cellular defense mechanism against viruses involving the cleavage of viral dsRNA by the enzyme DICER into siRNAs, which are then incorporated into the RISC complex to target and degrade complementary viral mRNAs.
Step-by-step explanation:
RNA interference (RNAi) is a natural defense mechanism in cells that protects against viral infections. This process involves several steps.
When a cell encounters foreign double-stranded RNA (dsRNA), typically of a viral origin, an enzyme called DICER attaches to it and cleaves the dsRNA into short fragments.
These fragments, known as small interfering RNAs (siRNAs), are then incorporated into a complex known as the RNA-induced silencing complex (RISC).
The antisense strand of the siRNA within the RISC complex is critical for targeting the viral RNA. It binds to any viral mRNA that has a complementary sequence.
Once bound, the mRNA is degraded, preventing the virus from using the host cell's machinery to replicate itself. This gene silencing is an important aspect of the immune response to viruses.
MicroRNAs (miRNAs), which are mostly complementary to mRNA transcripts, can also play a role similar to siRNAs by binding to and inhibiting the translation of mRNAs.
The miRNA-RISC complex binds to the target mRNA and if the miRNA is fully complementary, then the mRNA can be cleaved, similar to the siRNA mechanism.
The use of RNAi therapeutics, including siRNAs and miRNAs, represents a promising approach to treat viral infections by mimicking this natural cellular defense strategy.