Final answer:
siRNAs and miRNAs are crucial for gene silencing by binding to specific mRNA for degradation or translation repression through a process involving DICER cleavage and association with RISC.
Step-by-step explanation:
How siRNAs and miRNAs Function in Gene Silencing
Small interfering RNAs (siRNAs) and microRNAs (miRNAs) are pivotal in the process of gene silencing. siRNAs are perfectly complementary to their target mRNA and lead to its degradation upon binding, while miRNAs, which are often not completely complementary, can inhibit translation. The pathway for these processes starts with the transcription of double-stranded RNA molecules, which are then processed by a nuclease called DICER into shorter, roughly 20 nucleotide fragments. These small RNAs associate with RNA-induced silencing complex (RISC), and the siRNA-RISC complex directly binds to and cleaves complementary mRNA. In contrast, miRNA-RISC complexes may bind to mRNA to repress translation; if the miRNA is completely complementary to the mRNA, it can also lead to mRNA cleavage.
These mechanisms have significant potential for therapeutic applications, like treating viral infections or interfering with gene expression associated with diseases such as cancer. Researchers harness these natural pathways by creating custom-designed siRNAs to target specific genes, allowing the study of gene function and the development of new treatments. Moreover, miRNAs play a role in regulating endogenous genes, with hundreds of miRNAs each controlling multiple targets, which has links to various human diseases including cancer.