So basically what happens is if this is our mRNA molecule, if this is the premRNA molecule and this is the five end and this is the three end, what happens is a small section of the three end of the pre mRNA is cleaved, is removed and then we add a bunch of adenosine phosphates. How many? Well, anywhere from 200 to 250 adenosine molecules. Adenosine nucleotides are added to our tail, to our end and that's exactly why it's known as the polya or the poly adenosine tail. Now let's move on to the final type of post transcriptional modification and this is known as the process of splicing. So we remove regions known as the introns and we combine the regions known as the axons.