Final answer:
miRNA and siRNA play roles in post-transcriptional modification by binding to the RISC complex, leading to the degradation of target mRNA, thus regulating gene expression after the mRNA has been transcribed and before translation begins.
Step-by-step explanation:
The role of miRNA and siRNA in gene regulation is related to post-transcriptional modification. These types of RNA are involved in controlling gene expression after the mRNA is transcribed but before translation begins. miRNAs and siRNAs are processed in the nucleus and eventually form a complex with the RISC (RNA-induced silencing complex) to degrade target mRNA. This process ensures that aberrant or surplus mRNAs are not translated into proteins, thereby contributing to the regulation of gene expression. miRNAs are short RNA molecules, typically 21-24 nucleotides long, and play a crucial role in regulating various cellular processes, including development, differentiation, and metabolism. They are first transcribed as longer pre-miRNAs and then cut down to mature miRNAs by an enzyme called dicer. Once mature, they associate with RISC to guide it to the target mRNA, leading to its degradation or inhibition of translation. Similarly, siRNAs are another class of short double-stranded RNA molecules that also guide RISC to target mRNAs for degradation. Both miRNAs and siRNAs can control the levels of specific proteins in the cell by regulating the stability and translation of their corresponding mRNAs. This post-transcriptional regulation is crucial for maintaining proper cellular functions and for responding to environmental cues.