So if blue means we have these codons, then the entire mRNA molecule in prokaryotic cells consists of this blue region because these blue regions are the codons that express that particular sequence on the polypeptide chain. Now, for quite some time we thought the same exact thing was true in eukaryotic cells such as human cells. But in 1977, Philip Sharp and Richard Roberts basically discovered that this was not true when it came to mRNA in eukaryotic cells. In fact, in eukaryotic cells the newly synthesized mRNA molecule consists of these intron sections, these sequences of nucleotides that do not code for any protein and they also contain these exons which were the regions that contained the codons that did code for that particular polypeptide chain. So instead of looking like this one, instead of having a continuous blue section, the mRNA molecule and eukaryotic cells, such as our own human cells consist of these intervening sections known as introns. In fact, the int means intervening sequence of nucleotides.