Small RNA molecules play a critical role in gene expression regulation, particularly through mechanisms such as RNA interference (RNAi). They can post-transcriptionally modify mRNA, leading to its degradation or inhibiting its translation into proteins. This regulatory function helps control gene activity, ensuring that genes are expressed at the right times and levels, which is crucial for development, cellular differentiation, and response to environmental changes. Thus, small RNA molecules are integral to maintaining cellular homeostasis.