What part of mRNA is crucial for its stability and is located at the 3' end?

The 3' untranslated region (3' UTR) of mRNA plays a crucial role in the stability of the mRNA molecule. This region is found at the end of the mRNA transcript and is not translated into protein, but it contains sequences that are important for the regulation of mRNA stability, localization, and translation efficiency. The 3' UTR often includes binding sites for regulatory proteins and microRNAs, which can influence how long the mRNA persists in the cell before degradation.

In contrast, the 5' cap is important for mRNA recognition during translation initiation and protection from exonucleases, but it does not reside at the 3' end. Exons are coding regions that are translated into proteins, while introns are non-coding regions that are spliced out of the precursor mRNA before it matures. Neither exons nor introns are primarily involved in the stability of the mRNA like the 3' UTR is, solidifying the latter's role in mRNA persistence within the cell.