Eukaryotic Post-Transcriptional Regulation - Video Tutorials & Practice Problems
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Eukaryotic Post-Transcriptional Regulation
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In this video, we're going to begin our lesson on eukaryotic post transcriptional regulation. And so eukaryotes regulate gene expression at the post transcriptional level in 3 different ways that you can see numbered down below 123. And so the first way that they regulate their gene expression at the post transcriptional level after transcription is complete is through alternative RNA splicing. And alternative RNA splicing is going to result in different protein products coming from the same mRNA transcript transcript or the same gene, and we'll talk more about alternative RNA splicing as we move forward. Now the second level of post transcriptional regulation in eukaryotes is RNA processing by adding a 5 prime cap and a poly a tail to the mRNA in order to protect the RNA from degrading enzymes. And again, this is an idea that we'll talk more about moving forward as well. And then the third level of post transcriptional regulation in eukaryotes is that the mRNA can actually be tagged for degradation or transcription can be blocked, from the mRNA. Transcription of the mRNA can be blocked by small non coding RNA molecules. And we'll talk more about these small non coding RNA molecules as we move forward as well. And so this here concludes our brief introduction to eukaryotic post transcriptional regulation, and we'll be able to talk about all 3 of these different levels as we move forward. So I'll see you all in our next video.
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1) Alternative RNA Splicing
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In this video, we're going to talk about the first level of post transcriptional regulation in eukaryotes, and that is alternative RNA splicing. And so recall that way back in our previous lesson videos, we already covered alternative RNA splicing. And so if you don't remember anything about alternative RNA splicing, then make sure to go back and watch those older videos before you continue here. And so recall that eukaryotes require post transcriptional modifications like RNA splicing, which can alter gene expression. And so alternative splicing is really when different mRNA molecules are produced from the same premature RNA molecule or the same pre mRNA. And so another way to be able to phrase alternative splicing is, because there are different mRNA molecules produced, that's going to lead to different proteins being made from the same gene. And so different mRNA molecules will lead to different proteins being made Now recall that the spliceosome, Now recall that the spliceosome is the complex RNA protein, complex, that is going to remove introns from the pre mRNA and splice together the exons. And so if we take a look at our image down below over here again, we have our miniature map and you can see that we're focusing on RNA processing, and this is going to be a form of post transcriptional modifications the spl the splicing here that we're referring to. And so, up at the top here, what we have is the DNA, the specific gene of interest. And within the gene, the red regions here represent exons that are gonna be spliced together, and the blue regions represent introns introns that are going to be removed. And so, notice that, when the gene is first transcribed through transcription, it's a pre mRNA molecule or a pre mRNA transcript that is formed. And the pre mRNA molecule is, not going to be, the fully mature mRNA. It must undergo, splicing. And so over here, what we are zooming into is the spliceosome formation, which is going to be an assembly of, complex of RNA and protein that will come together to remove the introns, remove the blue regions, and splice together the red regions, the exons. And so that's what we're referring to here as RNA splicing. And alternative RNA splicing is when, RNA splicing can occur in multiple different ways. There are alternative pathways for RNA splicing to occur. And so here in this image, we're focusing on just 2 different alternative pathways for RNA splicing to occur. The first RNA pathway RNA splicing pathway is over here on the left hand side, which is showing you exons 123 all being expressed. And this is going to be the fully mature this is the mature mRNA that's ready for translation. And so this is one possibility for the RNA to get spliced, and that would create this particular circular protein product upon translation. But the alternate RNA splicing pathway over here, notice, has a different mature mRNA transcript where exon 3, notice, is not available over here. It's not present. And so exon 3 acted as an intron, in this alternative RNA splicing pathway. And so exon 3 was removed as an intron. And so only exons 1, 2, and 4 are available over here. And that creates a shorter polypeptide chain and that ultimately leads to a different protein. And so by filtering and controlling alternative RNA splicing, a specific gene product, can be redirected to create a new gene product. And so this is a way of regulating gene, expression. And so this is a post transcriptional method because, the alternative RNA splicing is occurring after transcription has occurred. And so this here concludes our, brief review and introduction here of alternative RNA splicing. And we'll be able to get some practice applying this as we move forward and talk about the other forms of post transcriptional regulation. So I'll see you all in our next video.
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Problem
Problem
Alternative RNA splicing has been estimated to occur in more than 95% of multi-exon genes. Which of the following is not an evolutionary advantage of alternative RNA splicing?
A
Alternative RNA splicing increases diversity without increasing genome size.
B
Different protein variants can be expressed by the same gene in different tissues.
C
Alternative RNA splicing creates shorter mRNA transcripts.
D
Different protein variants can be expressed by the same gene during different stages of development.
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concept
2) mRNA Protection in the Cytoplasm
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In this video, we're going to talk about the second level of post transcriptional regulation which is mRNA protection in the cytoplasm. And so mRNA transcripts must be transported to the cytoplasm of the cell in order for the mRNA transcript to be translated by ribosomes and create a protein product. But the problem is is that the cytoplasm actually has many RNA degrading enzymes. And so the mRNA transcripts when they go out to the cytoplasm, they are at risk of being degraded by these RNA degrading enzymes. Now these RNA degrading enzymes are there to help destroy foreign viral RNA molecules. So they are going to act as a defense mechanism against viral RNA molecules. Now in order for the mRNA transcripts to be protected, the mRNA needs to be processed so that it has a 5 prime cap added, as well as a poly a tail added as well. And so the 5 prime cap and the poly a tail, which is added to the 3 prime end of the molecule, that is going to protect the mRNA from degradation by enzymes. And so this, degradation feature and, non and protection feature, degradation and protection is a way of regulating gene expression. And so let's take a look at our image down below to get a better understanding of this. And so, notice the example here says that mRNA is protected from degradation by cytoplasm enzymes with a 5 prime cap and a poly a tail. And so RNA processing, which is the addition of the 5 prime cap and poly a tail occurs within the nucleus. But of course, the RNA needs to be transported to the outside, into the cytoplasm of the cell. And so it needs to be transported outside the nucleus into the cytoplasm of the cell. And so that's what you see here. Here we have the nucleus, this entire box here is representing a cell. And within the cell we have the nucleus of the cells right here. And within the nucleus you can see we have our, mature mRNA here, and it must be transported out of the nucleus. Now if the mRNA is not protected, if it does not have a 5 prime cap and a poly A tail, then it's going to be an unprotected mRNA, and that's going to lead to degradation. So the unprotected mRNA is degraded over here and notice that it's being chopped up into a bunch of tiny little pieces. And then in that case, the final gene product, the protein is not going to be created. And so this is a way of turning off the gene is through, making sure that the RNA is unprotected. That will turn off the gene. Now, of course, if the RNA is properly protected with the 5 prime cap and the poly a tail, then we have protected mRNA that will not be degraded. And this protected mRNA that's not degraded, it can therefore be translated into a protein. And of course, when it's translated into a protein, the final gene product is being made, and so this is a way of turning on the gene. And so you can see the off and the on, this is a way of regulating gene expression to turn on or turn off genes. And so this here concludes our, introduction to this second level of post transcriptional regulation, and we'll be able to get some practice applying these concepts as we move forward, as well as talk about the 3rd and final level of post transcriptional regulation. So I'll see you all in that video.
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concept
3) RNA Interference
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In this video, we're going to talk about the 3rd level of post transcriptional regulation in eukaryotes, and that is RNA interference. And so RNA interference is commonly abbreviated as just RNA I with a lowercase I here. And so RNA interference or RNAi is really just the process of small non coding RNAs blocking translation of target mRNA molecules. And so these small non coding RNAs are really just short strands of RNA that have a complementary sequence to an mRNA target. And so we'll be able to see more and learn more about them down below in our image. Now really there are 2 possible scenarios that are gonna turn gene expression off when it comes to RNA interference. And so the first possible scenario is mRNA is going to be degraded and targeted for degradation. And then, the second possible scenario is going to be that the ribosome is going to be blocked from binding and that's going to prevent translation. And so let's take a look at our image down below where you can see in our example, RNA interference can block ribosome binding or recruit cellular enzymes for mRNA degradation. And so over here on the left hand side, notice that we're showing you our miniature version of the map, and you can see that again mRNA degradation and translational, control is going to occur in the cytoplasm of the cell outside of the nucleus. And so up here, notice in this image where this image we're focusing on RNA interference or RNAi. And, notice that it it's going to require small non coding RNAs, like this little short orange RNA molecule that you see at the top. And this short small non coding RNA is complementary to a small sequence on the mRNA itself, the messenger RNA. And so, there are two levels here. There is the mRNA degradation scenario, and then there is the translational control scenario. So in the mRNA degradation scenario, what happens is the small noncoding RNA is going to complementary bind to the mRNA, and the mRNA is going to be degraded. It's going to be degraded by enzymes. And so the small noncoding RNA here is basically marking the mRNA for degradation. And so you can see that this enzyme over here is degrading the mRNA into small tiny pieces. And of course, the gene product will not be made if the mRNA is being degraded. And so this is a way of turning off the gene expression. Now if we take a look at the translational control scenario, what happens is the mRNA, the small noncoding RNA complementary binds to the mRNA. But in this scenario, when the, small noncoding RNA binds to the mRNA, the mRNA is not going to be degraded. Instead, the ribosome is not going to be able to bind to the mRNA as it normally would to translate it. And so in this scenario, the ribosome is blocked from binding to the mRNA. And of course that is also going to prevent the gene product, the protein from being made. And so that is also going to be turning off gene expression. And so, this here RNA interference is basically interfering with the mRNA and turning off the expression of the mRNA. And so this here concludes our introduction to RNA interference, and 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
Which of the following statements best describes the function of RNAi?
A
Small RNA molecules interfere with translation by targeting ribosomes for degradation.
B
Small DNA molecules interfere with mRNA molecules by blocking their ability to bind to a ribosome.
C
Small RNA molecules interfere with translation by targeting specific tRNA molecules
D
Small RNA molecules interfere with translation by blocking a target mRNA's ability to bind to a ribosome.
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concept
Types of Small Noncoding RNAs
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3m
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In this video, we're going to introduce 2 different types of small non coding RNAs. And so again, there are 2 classes classes of RNAs that are involved in RNAi or RNA interference. And so the first class is going to be the microRNAs, and the second class are going to be the small interfering RNAs or, for short, the s I RNAs. And so both types of RNA, the micro RNAs and the small interfering RNAs are going to bind to a target mRNA by complementary base pairing and it's going to turn off expression of a gene, through RNA interference. So both micro RNAs and small interfering RNAs will turn off expression of a gene. And so what is the difference between the 2? Well, the only difference between micro RNAs and siRNAs is the structure of their precursor form. And so microRNAs have a single stranded precursor, and siRNAs have a double stranded precursor. And so we can take a look at this, in our image down below. And so notice in this example, we're showing you RNA interference by 2 types of small non coding RNAs, the micro RNAs and the siRNAs. And so once again, over here on the far left, we have our miniature version of the map of our lesson, and, notice that, RNA interference is really taking place here with mRNA degradation, which is going to occur in the cytoplasm, but it also is going to block translation as well, and so it is a type of translational regulation as well here. And so, over here on the left hand side, notice that we're focusing on the micro RNAs. And the micro RNAs are going to have a single stranded precursor, and so this is the precursor for the microRNA. And then the microRNA is going to complimentary bind to the mRNA itself, and it is going to block, transcription or I'm sorry. It's going to block, the next step, either mark the molecule for degradation or block the ribosome from binding and block translation. And so it is a way of turning off the gene. Now over here on the right hand side, we're focusing on the siRNAs, the small interfering RNAs, and they have a double stranded precursor. And so notice that up above, we're showing you a double stranded precursor molecule. And so, ultimately, it will be, converted into a single stranded siRNA, and it's going to be very, very similar, under both conditions. They both are gonna be complementary binding to the mRNA. And again, it can either mark the mRNA for degradation or it can block the ribosome from translating. And so in either case, it is going to be interfering with the RNA. It is a type of RNA interference, and it will be turning off the gene. And so really, the main learning objective here is that the micro RNAs are gonna have single stranded precursors whereas the s r RNAs are gonna have double stranded precursors. But other than that, they're going to be very, very similar in their functions. And so this here concludes our introduction to the different types of small non coding RNAs, and 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
Which of the following best describes siRNA?
A
A short double-stranded RNA with one strand that can complimentarily bind to and inactivate an mRNA.
B
A single-stranded RNA with internal complementary base pairs that allow it to fold into a cloverleaf pattern.
C
A portion of rRNA which is a component of the large and small ribosomal subunits.
D
A molecule, known as Dicer, that can degrade or cut RNA sequences.