What is added to the 5' end of some eukaryotic transcripts?

In eukaryotic cells, the 5' end of newly transcribed messenger RNA (mRNA) is modified by the addition of a 5' cap. This 5' cap, which consists of a modified guanine nucleotide, serves several critical functions. It protects the mRNA from degradation by exonucleases, facilitates the export of the mRNA from the nucleus to the cytoplasm, and is essential for the initiation of translation.

The cap also plays a role in ribosome binding during the translation process, ensuring that the mRNA can be effectively translated into a protein. This modification is crucial for proper gene expression and regulation in eukaryotic cells.

In contrast, while introns and exons are components of the gene itself, with introns being non-coding sequences that are removed during mRNA processing and exons being the coding sequences that remain, they do not specifically pertain to the addition at the 5' end of the transcript. The poly A tail is added to the 3' end of the mRNA and serves different functions, such as enhancing stability and aiding in the termination of transcription. Thus, the addition of the 5' cap is a distinct and essential modification that occurs at the