Eukaryotic RNA Processing and Splicing - Video Tutorials & Practice Problems
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Eukaryotic RNA Processing and Splicing
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In this video, we're going to begin our lesson on eukaryotic RNA processing and splicing. And so recall that we mentioned in some of our previous lesson videos that unlike prokaryotic mRNA, it turns out that eukaryotic mRNA is going to require further modification upon transcription termination. And that's because eukaryotic organisms, upon transcription termination, the mRNA is not fully mature. It's a premature mRNA, otherwise termed a pre mRNA. And so this pre mRNA that's originally formed in eukaryotic organisms is the eukaryotic mRNA before modification via RNA processing and splicing. And so RNA processing and splicing are just these eukaryotic processes that convert this premature mRNA or pre mRNA into a fully mature mRNA that's actually ready for translation. And again, this is only a process that applies to eukaryotic organisms, not to prokaryotic organisms. And so if we take a look at our image down below, notice over here on the left hand side, this is representing the premature mRNA or the pre mRNA that's originally formed during eukaryotic transcription. But this pre mRNA is premature. It's not ready for translation. In order to prepare this pre mRNA for translation, it has to undergo RNA processing and splicing. And so RNA processing and splicing are going to be these eukaryotic processes that help convert the pre mRNA into a modified version of the mRNA that is ready and fully mature and ready for translation. And so as we move forward in our course, we're going to talk about exactly what's entailed in RNA processing and in RNA splicing to help convert the pre mRNA to this modified mRNA over here. And so we'll get to talk more about that as we move forward. So I'll see you all in our next video.
2
concept
1) RNA Processing
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4m
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In this video we're going to talk about RNA processing. And so RNA processing only occurs in eukaryotic organisms, not in prokaryotic organisms. And so eukaryotic RNA processing involves 2 events that are gonna alter both ends of the premature mRNA, or the pre mRNA. And so the first event is going to be the addition of a 5 prime cap, which is really just a modified guanine nucleotide that's going to be added specifically to the 5 prime end of the pre mRNA. And then the second event that's going to alter the end of the pre mRNA is the addition of a poly a tail. And the poly a tail is really just a sequence of a bunch of adenine nucleotides that are gonna be added specifically to the 3 prime end of the pre mRNA. And so both of these alterations are going to modify the ends of the pre mRNA. And so 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. And so this pre mRNA, we know that in eukaryotic cells is going to go undergo RNA processing, which involves modifying the end of the pre mRNA. So you can see the ends are being modified. The first modification involves the addition of a 5 prime cap, which is added to the 5 prime end of the RNA molecule. And, again, the 5 prime cap is really just a modified guanine nucleotide. Now on the 3 prime end of the RNA molecule, it is also going to be modified, but with a poly a tail. And the poly a tail is just a stretch of a bunch of adenine nucleotides that are added to the 3 prime end of the RNA molecule. Now you might be wondering, why is it that the 5 prime cap and the poly a tail need to be added to the RNA. And so it turns out that the 5 prime cap and the poly a tail actually share several important functions, including the following functions that we are listing down below. The 5 prime cap and poly a tail are both important for facilitating exports 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, which, again, we'll talk more about translation later in our course. But the 5 prime cap and poly A tail are really important to export the mRNA from the nucleus to the cytoplasm. Now the 5 prime cap and poly A tail are also really important to protect the mRNA from degradation by enzymes. And so the addition of the 5 prime cap and the poly a tail helps to, again, protect the mRNA from degradation by enzymes that might otherwise degrade the RNA. Now lastly, the 5 prime cap and poly a tail are both important for helping ribosomes attach to the mRNA for translation to take place. And so 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. And so these ribosomes need to be able to attach to the mRNA, and the 5 prime cap and poly A tail play a role in that attachment. And so, this here is going to conclude our brief introduction to RNA processing. And so in our next video, we'll be able to talk about RNA splicing. So I'll see you all in that video.
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Problem
Problem
Which of the following processes occurs in eukaryotic gene expression?
A
mRNA, tRNA, and rRNA are translated.
B
A cap is added to the 5′ end of the mRNA.
C
Adenine nucleotides are added to the 5' end of the mRNA.
D
RNA polymerase requires tRNA to elongate the molecule.
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Problem
Problem
A mRNA poly-A tail:
A
Prevents translation.
B
Prevents transcription.
C
Marks the RNA for degradation.
D
Protects the mRNA from degradation.
5
concept
2) RNA Splicing Creates Mature mRNA
Video duration:
8m
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Video transcript
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. And so it's important to note that even within eukaryotic genes, within the DNA of eukaryotes, there are regions that are called introns and exons. Now 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. And so when eukaryotic genes are transcribed, they're going to be transcribed into the premature mRNA. And so the premature or the pre mRNA is going to contain introns and exons. Now RNA splicing is going to be the eukaryotic process that is important for removing some of the regions of the pre mRNA, specifically the introns are going to get removed. And RNA splicing involves the reconnecting of the remaining regions of the, pre mRNA, which are going to be the axons. And so notice that, down below, we're saying that introns, which starts with IN, are going to be non coding regions of DNA and RNA, meaning that they do not actually code for amino acids or proteins. And these non coding regions of DNA or RNA are going to intervene or interrupt the coding regions of the DNA and RNA. And so these introns do not get translated. They do not get turned into protein. Now, the introns, because it starts with IN, the IN and introns can hopefully help remind you that they are intervening and interrupting, which also start with IN. Now the exons, on the other hand, starts with EX, and exons are coding regions of the DNA and RNA that ultimately do get expressed, and so that means that they do actually get translated into protein. And so we'll get to talk more about translation later in our course. But, ultimately, what we're seeing here is that within the DNA and RNA, originally, there will be introns and there will be exon regions. The introns need to get removed, and the exons need to be reconnected and get expressed. Now the spliceosome is the large cellular complex of RNA and protein that's gonna be responsible for removing the introns and splicing together or reconnecting the exons. And so if we take a look at our image down below, we can get a better understanding of these introns and exons and RNA splicing. And so it says here that the spliceosome is going to remove introns from the pre mRNA transcript after transcription. And so if you take a look at the top here, what this is representing is the DNA, the eukaryotic DNA, which we know eukaryotic DNA has a promoter region, which is going to initiate transcription, and it has a terminator region at the end, which is going to terminate or end transcription. And in between, what we have is the coding region. But in this coding region, there are re some regions that are going to be exons and other regions of the DNA that are going to be introns, and so the exons in this image are represented by these reddish regions, and the introns are, of course, represented by the bluish regions. And so, the exons and introns are found in the DNA. And so when the DNA gets transcribed, when it undergoes transcription, the premature mRNA is going to be built. The premature mRNA transcript or molecule will be built. And so, what you'll notice is that the premature mRNA contains both exons and introns. And again, the introns are kind of intervening or interrupting the coding region. So you'll see the introns are kind of in between and interrupting the exons, which ultimately get expressed. And so if you zoom in over here, what we're showing you is the spliceosome formation, which recall that the spliceosome is this really large complex of RNA and protein responsible for removing introns and splicing together or reconnecting the exons. And so the spliceosome here is forming, and what you'll notice is that the blue region, the exons, are being pinched off and they're ultimately going to get removed. And the exons, these red regions here, are going to get reconnected. And so this is here representing RNA splicing. And so, RNA splicing ultimately is going to lead to a mature mRNA transcript. And so, when you take a look at these mature mRNA transcripts, you'll see that they've been processed. RNA processing has occurred because it's got the 5 prime cap over here, guanine cap, and it's got the poly a tail. And notice that all of the introns have been removed, all of these blue regions have been removed through RNA splicing, and the exons have been reconnected. And the exons ultimately get expressed, which means that they will be translated into a amino acid sequence to ultimately help form a protein, which is down below. Now, it turns out that there is alternative RNA splicing. There are, there's something known as alternative RNA splicing, which means that single genes can actually be spliced in different ways, in order to give multiple products. And so that's what we're showing you up above, how this premature mRNA transcript can actually be spliced in multiple ways, where, what you'll notice is over here, exons 1, 2, 3, and 4 are all being expressed, but over here on the right hand side, only exons 1, 2, and 4 are being expressed and exon 3 is not being expressed because with alternative splicing, exon 3 actually acts as an intron with this alternative splicing, so exon 3 was removed. And so what we can see here is that in on in some scenarios, exons may actually act as exons, but in other scenarios some exons will act as introns and get removed. And so we have a shorter, mature mRNA transcript or mRNA molecule here because it's missing exon 3. Notice there's no exon 3. And so that's going to lead to a shorter amino acid sequence upon translation, and that will ultimately lead to a different protein with a different shape. And so this protein and this protein are different proteins with different structures, different shapes, and ultimately different functions. And so what you can see is that you can have a single gene, a single segment of DNA, that can lead to multiple protein products depending on how the RNA is spliced through alternative RNA splicing. And so this here concludes our brief introduction to RNA splicing and how it helps to create a mature mRNA that's ready for translation. And, again, this only occurs in eukaryotic organisms. And so 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.
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Problem
Problem
The regions in DNA & RNA that encode actual gene products are known as: