In this video, we're going to talk about RNA splicing and how RNA splicing helps to create mature mRNA molecules. Now recall that RNA splicing is a eukaryotic process that only occurs in eukaryotes, but does not occur in prokaryotes. It's important to note that even within eukaryotic genes, within the DNA of eukaryotes, there are regions that are called introns and exons. We'll introduce what these introns and exons are very shortly here, but it's important to note again that these eukaryotic genes have introns and exons. When eukaryotic genes are transcribed, they're going to be transcribed into the pre-mature mRNA, which will contain both introns and exons.
RNA splicing is the eukaryotic process that is important for removing some of the regions of the pre-mRNA, specifically the introns are going to get removed. RNA splicing involves the reconnecting of the remaining regions of the pre-mRNA, which are going to be the exons. Notice that introns, which start with 'IN', are non-coding regions of DNA and RNA, meaning that they do not actually code for amino acids or proteins. These non-coding regions of DNA or RNA intervene or interrupt the coding regions of the DNA and RNA. Introns do not get translated; they do not get turned into protein. Introns, because they start with 'IN', can help remind you that they are intervening and interrupting, which also start with 'IN'.
On the other hand, exons start with 'EX', and exons are coding regions of the DNA and RNA that ultimately do get expressed, meaning that they do actually get translated into protein. We'll talk more about translation later in our course. Within the DNA and RNA, there will be regions of introns and exons. The introns need to get removed, and the exons need to be reconnected and expressed. The spliceosome is the large cellular complex of RNA and protein that's going to be responsible for removing the introns and splicing together, or reconnecting the exons.
If you look at our image below, we can get a better understanding of these introns and exons and RNA splicing. It says here that the spliceosome is going to remove introns from the pre-mRNA transcript after transcription. At the top, what this represents is the eukaryotic DNA, which has a promoter region, initiating transcription, and a terminator region at the end, which terminates transcription. In between, we have the coding region. But in this coding region, some regions are going to be exons and other regions will be introns. Exons are represented by these reddish regions, and introns by the bluish regions. When the DNA is transcribed, the premature mRNA is going to be built. Premature mRNA contains both exons and introns, where introns intervene or interrupt the coding region. If you zoom in here, we show the spliceosome formation, which, recall, is a large complex responsible for removing introns and splicing together the exons.
Notably, the blue regions, the exons, are being pinched off and ultimately get reconnected. This process is representing RNA splicing, which ultimately leads to a mature mRNA transcript. When you look at these mature mRNA transcripts, you'll see that they have been processed through RNA processing, which includes a 5-prime cap, a guanine cap, and a poly-A tail. All the introns have been removed through RNA splicing, and the exons have been reconnected. The exons ultimately get expressed, which means that they will be translated into an amino acid sequence to help form a protein.
There is also something known as alternative RNA splicing, which means that single genes can be spliced in various ways to yield multiple products. The premature mRNA transcript can be spliced in multiple ways; for example, exons 1, 2, 3, and 4 are all being expressed, but only exons 1, 2, and 4 are expressed in another scenario, and exon 3 is not expressed because, with alternative splicing, exon 3 acts as an intron. This results in a shorter, mature mRNA transcript or molecule because it's missing exon 3. This leads to a shorter amino acid sequence upon translation and ultimately to a different protein with a different shape. These different proteins have different structures, shapes, and ultimately different functions. This shows how a single segment of DNA can lead to multiple protein products depending on how the RNA is spliced through alternative RNA splicing.
This concludes our brief introduction to RNA splicing and how it helps to create mature mRNA that's ready for translation. This process only occurs in eukaryotic organisms. We'll be able to get some practice applying these concepts as we move forward in our course, so I'll see you all in our next video.
