Master Post Transcriptional Modification in Eukaryotes

After transcription, eukaryotic cells have certain modifications made to mRNA before it is fully functional. These modifications occur in the nucleus, which is the location of the mRNA template before proteins are synthesized from it. Splicing of the mRNA occurs, as introns are cut out and exons are spliced together. Introns are the non-coding regions to be removed, while exons contain the codes for functional protein. This allows for the mRNA to be one full continuous functional piece. Alternate splicing can occur, which is the inclusion of particular exons resulting in two different protein isoforms. To prevent damage to the mRNA, a 5’ cap is added as a modified guanine that prevents RNases from destroying the newly-created mRNA. Also, a 3’ poly A tail is added, which is a long series of adenine nucleotides that serve as a buffer against damage from exonuclease activity. The RNA is then transported to the cytosol for protein synthesis.