How do siRNA and miRNA regulate gene expression?

siRNA (small interfering RNA) and miRNA (microRNA) are crucial components in the post-transcriptional regulation of gene expression. Their primary mechanism involves binding to complementary mRNA molecules. When siRNA or miRNA binds to an mRNA with a matching sequence, it can either block the translation of that mRNA into protein or lead to its degradation.

For siRNA, the typical outcome is the degradation of the mRNA, while miRNA often inhibits translation without inducing degradation, although in some cases, it can also lead to mRNA decay. Nevertheless, the central function shared by both siRNA and miRNA is the ability to bind to specific mRNAs and regulate their availability to the translational machinery, hence blocking the protein synthesis process. This is a pivotal mechanism of gene expression regulation in various biological pathways.

The correct understanding of this functional aspect shows why the option regarding binding to complementary mRNAs and blocking translation captures the essence of how siRNA and miRNA operate in gene expression modulation.