But for those genes that are very, very large, for example, tens of thousands of nucleotides long, we can have as many as hundreds of these intros in a given gene. Now, the question is once the eukaryotic cell actually synthesizes this premRNA molecule, so this mRNA molecule that is not in its fully functional and modified form is commonly known as the precursor mRNA, the pre mRNA or the primary mRNA. And so once we form the primary mRNA molecule how exactly do we modify this molecule and at what stage do we actually take out these introns? Well, basically within our cell we have this complex of special proteins and special RNA molecules that aggregate and combine together to form a complex, a structure known as a splicosome. And the splicosome is responsible for essentially locating these introns, removing the introns while at the same time gluing together splicing together those exons. And this can be seen in the following diagram.