Post-transcriptional modifications (PTMs) are processes that facilitate the generation of mature, functional RNA. These rapidly responsive regulatory mechanisms allow different proteins to be produced from one gene and act as regulators of the phenotype and proliferation rate. These modifications also play a role in some forms of cancer and neurodegenerative diseases. The pre-messenger RNA (mRNA), called heterogeneous nuclear RNA (hnRNA), is modified by adding a 5’ 7-methylguanosine cap and a 3’ poly-A (polyadenylate) tail for stability and protection. Moreover, hnRNA that contains introns (noncoding sequences) among the expressed sequences or exons undergo splicing. This process removes introns to produce a mature mRNA carrying the coding sequence for translation. Alternative splicing, on the other hand, also excludes the introns, but varying combinations of exons are linked, producing different proteins from the original mRNA. In RNA editing, the mRNA sequence is altered and differs from the transcribed DNA template. Transfer RNA and ribosomal RNA start from longer precursor molecules and go through steps that include methylation, trimming, and addition of nucleotides.