Final answer:
MicroRNAs (miRNAs) are short endogenous RNA molecules that regulate gene expression at the post-transcriptional level in eukaryotic cells by binding to and degrading target mRNA molecules. They play key roles in various cellular processes and are associated with diseases such as cancer.
Step-by-step explanation:
MicroRNAs (miRNAs) are short endogenous RNA molecules that perform the function of regulating gene expression at the post-transcriptional level in eukaryotic cells. They bind to target mRNA molecules and facilitate their degradation, preventing the synthesis of proteins. miRNAs are transcribed from genes and are involved in various cellular processes, including development and disease states such as cancer.