In this video, we're going to talk about RNA processing. RNA processing only occurs in eukaryotic organisms, not in prokaryotic organisms. Eukaryotic RNA processing involves two events that are going to alter both ends of the premature mRNA, or the pre-mRNA. The first event is going to be the addition of a 5' cap, which is really just a modified guanine nucleotide that's going to be added specifically to the 5' end of the pre-mRNA. The second event that's going to alter the end of the pre-mRNA is the addition of a poly A tail. The poly A tail is really just a sequence of a bunch of adenine nucleotides that are going to be added specifically to the 3' end of the pre-mRNA. Both of these alterations are going to modify the ends of the pre-mRNA.

If we take a look at our image down below, what you'll notice is over here on the left-hand side, what we've got is our premature mRNA, our pre-mRNA immediately after transcription. This pre-mRNA, we know that in eukaryotic cells, is going to undergo RNA processing, which involves modifying the end of the pre-mRNA. You can see the ends are being modified. The first modification involves the addition of a 5' cap, which is added to the 5' end of the RNA molecule. Again, the 5' cap is really just a modified guanine nucleotide. Now, on the 3' end of the RNA molecule, it is also going to be modified, but with a poly A tail. The poly A tail is just a stretch of a bunch of adenine nucleotides that are added to the 3' end of the RNA molecule.

You might be wondering why it is that the 5' cap and the poly A tail need to be added to the RNA. It turns out that the 5' cap and the poly A tail actually share several important functions, including facilitating the export of the mRNA from the nucleus, where it's first transcribed in eukaryotic organisms, to the cytoplasm where the RNA molecule needs to be in order for translation to take place. We'll talk more about translation later in our course. But the 5' cap and poly A tail are really important to export the mRNA from the nucleus to the cytoplasm. The 5' cap and poly A tail are also really important to protect the mRNA from degradation by enzymes. The addition of the 5' cap and the poly A tail helps to protect the mRNA from degradation by enzymes that might otherwise degrade the RNA.

Lastly, the 5' cap and poly A tail are both important for helping ribosomes attach to the mRNA for translation to take place. We'll be able to talk again more about translation later in our course. But, these ribosomes are cellular structures that are important for translation. These ribosomes need to be able to attach to the mRNA, and the 5' cap and poly A tail play a role in that attachment. This concludes our brief introduction to RNA processing. In our next video, we'll be able to talk about RNA splicing. So, I'll see you all in that video.