What are microRNAs (miRNAs)?

MicroRNAs (miRNAs) are small, single-stranded RNA molecules that play a crucial role in the regulation of gene expression. These molecules typically range from 20 to 24 nucleotides in length and are known to bind to complementary sequences on target messenger RNAs (mRNAs). This binding often leads to the degradation of the mRNA or inhibition of its translation into protein, thereby downregulating the expression of the corresponding gene.

The primary function of miRNAs is to fine-tune the expression of genes, allowing cells to adapt to changes in their environment and maintain homeostasis. They are involved in various biological processes, including development, differentiation, and responses to stress. The precise targeting of mRNAs by miRNAs is vital for proper cellular function and for the regulation of numerous pathways.

In contrast to the other choices, large RNA molecules involved in protein synthesis are typically ribosomal RNA (rRNA) or messenger RNA (mRNA), not microRNAs. The mention of RNA fragments that assist in DNA replication does not pertain to miRNAs, as replication is primarily facilitated by enzymes and is not impacted directly by small RNA molecules. Finally, while protein molecules that assist in RNA splicing are essential for processing pre-mRNA, they are distinct