Post-transcriptional modification refers to the processes that occur to messenger RNA (mRNA) after it is synthesized from DNA but before it is translated into a protein. These modifications include the addition of a 5' cap and a poly-A tail, which help protect the mRNA from degradation and assist in its export from the nucleus to the cytoplasm. Additionally, post-transcriptional modifications can involve splicing, where non-coding regions called introns are removed, and coding regions known as exons are joined together. This process ensures that the mRNA is properly formatted for translation, allowing for the correct synthesis of proteins essential for cellular functions.