Post-Transcriptional Regulators

Hi in this video we're gonna be talking about post transcription regulation. So we've talked about all these different kinds of gene regulation. But these videos are going to focus on what controls gene expression after the transcript has been transcribed. So the first thing that is really responsible for controlling gene transcription is going to be RNA processing translation and degradation. So how the cell handles the RNA. So regulation of M. RNA after transcription is a major rate to control gene expression. So these are things that we've already gone over for the most part. So these are like RNA processing, seeing events like splicing or export or editing because improperly processed RNA is actually remain in the nucleus and are not exported or translated for RNA translation that can also be controlled. Um So if you remember these proteins called E. I. S. Which are a factor involved and necessary for translation um they can also act to inhibit translation. And so um for instance if they become phosphor related they have they no longer can hide relies G. T. P. In exchange for G. D. P. And therefore they cannot promote translation. So this is another form of regulation. If they can't be translated then of course it's not going to be expressed. Also there are things called translational repressors and these are proteins that control um translation of an R. N. A. Um at a variety of different factors but all of these things are impacting translation and therefore impacting gene expression. Now another thing to consider is actually the rates of degradation of M. R. N. A. So M. RNA degradation rates actually vary between transcripts and is another way to control gene expression. So for instance M. RNA is with shorter poly A tails, they're less stable and so they get degraded more quickly than those with longer tails. Um And there's a few ways that M. R. And S get degraded in each of these ways is regulated in its own fashion. So one is X. Zones and these are you know, these complexes that degrade M. R. N. A. From three prime to five prime using extra nucleus is you have peabodys and these are actually nuclear M. RNA processing bodies. So these are regions of the nucleus um that also degrade M. R. N. A. And then you also have nonsense mediated decay. And so this decay or degradation is focused on improperly spliced M. R. N. A. And so for instance if the stock code on for instance gets put in the wrong place due to some kind of mutation, then it's sliced wrong and nonsense mediated decay, recognizes that and controls gene expression by degrading the RNA. So this is just an example of all the different ways or all the different steps that RNA can be regulated. So we have our D. N. A. Up here it gets transcribed but we're really focused on everything that happens after that so that and choose having the mature M. RNA. So if it's if it's not properly processed it doesn't ever properly become mature, it won't get exported. But if it is mature and it does get exported but we can control it actually a translation by a variety of different translation factors. And then any M. RNA. That you know doesn't need to be expressed for some reason can also be degraded in a variety of ways. So now let's turn the page.

So in this video we're going to be talking about another way of post transcription aly controlling gene expression and that's through RNA interference. So RNA interference is just using regulatory RNA is to control gene expression. So one of these types of RNA that can control gene expression are called small interfering RNA. Or S. I. R. N. A. S. And this is actually a way that's evolved um that uses RNA. Is to protect cells from viruses. And so this is because viruses typically you know you don't want those genes expressed. And so this is the way the bodies evolved to handle those. And so um S. R. N. A. They are double stranded RNA. Is that enter cells um once inside the cell um they interact with this enzyme called dicer. And this cleaves the S. I. R. N. A. S. Into really small fragments. These fragments then bind what's known as the risk complex. And um one of the, so this is a double stranded RNA. So that degrades it into become one strand. And then that single strand can then buy a complementary M. R. N. A. And then be degraded by risk. So the component of risk responsible for this degradation is called Argonaut. So let's look at what this looks like. We have this double stranded RNA that's usually come from some kind of virus or bacteria or whatever. And it inter cells. Yeah when I insert the cells dicer comes in and cleaves it into various fragments. Remember this is double stranded still it's been loaded onto the risk complex which you can see here. And um this eventually degrades one of the strands which which sort of goes off and does whatever and you have a risk bound to one of the strands of S. R. N. A. This can then go back and bind to M. R. N. A. That the virus has you know tried to create in the cell and when it's bound here it actually goes and it gets degraded. So that is one way that gene expression from foreign objects or foreign you know molecules gets degraded by the cells. But there is another way that RNA interference works and that's through MICRO RNA. So this is um but micro RNA differs because it's actually encoded in the genome. So how this works is so M. I. R. Nasr actually begin a single stranded RNA. S. That are created through transcription. Subnormal transcription of the genome. After transcription the M. RNA, the MIc the micro RNA is actually form these things called hairpins or loops. But essentially what those are is just they just fold on each other and create these secondary complex structure. Then draw OSHA recognizes these structures and comes in cleaves them off. And the free micro RNA can then associate with risk. Remember this is the same as the S. I. R. N. A. Then when it's associated with risk. The single stranded micro RNA can then bind to the three prime what's known as the U. T. R. Untranslated region of an M. R. N. A. And inhibit expression because it gets degraded by risk. Um And so this is a really large way that the cell regulates gene expression because each micro RNA can regulate around 200 M. RNA by controlling their degradation. So how this works. Let's go through these steps here. So we have our gene in the genome where our micro RNA in the genome it gets transcribed. Now it's transcribed and it forms into these structures here and remember they have hairpins or loops but there are these sort of complex structures. Hair pins then draw OSHA comes in and sort of cleaves off different regions of the micro RNA to fully process it. This gets exported into the side of saul. All of this has happened in the nucleus from here. When the P. R. M. N. A. Is pre micro RNA is in the side of salt. It interacts with dicer dicer again comes on and helps cleave it to make sure that it's the single stranded RNA. And when it is a single stranded RNA, it combined to the risk complex and this risk complex goes on and binds or let me draw it this way it goes on and binds the three prime U. TR. Of M. R. N. A. S. For degradation. So you can imagine this controls a lot of different genes because if the M. R. And S get degraded, they can't be expressed. So that's s. I. RNA. Micro RNA. S. Which are extremely important in genetics and cell biology. But there's also a couple more that I haven't really talked about. But I just want to mention briefly these are sort of lesser known ones but still important to realize um fishing can be regulated by other other RNA, including peewee interacting RNA is um that suppressed the movement of transpose sins and also long non coding RNA. S. Which are greater than 200 nucleotides in length but also act in their own mechanisms to regulate gene expression. So RNA interference is a major way that genes are regulated generally by those RNA interacting with an M. R. N. A. And then causing that M. RNA to become to become degraded. So now let's move on.

So in this video we're gonna be focusing on protein regulation of gene expression. So these are things that happen to proteins after they've already been created to either suppress or activate gene expression. So um of course we've already talked about this but regulating M RNA after transcription is a major method controlling gene expression. Um And that also you know that controls translation or RNA editing or various RNA interference. But protein modifications can also inhibit or activate protein function. So some modifications of proteins that we've talked about before but I just want to bring up again as examples of ways that this could actually impact gene expression are things like protein phosphor relation. De phosphor relation which control phosphates and activity of a protein but also protein cleavage. And these are all modifications that can happen to regulate gene expression by regulating the protein. Another way is protein degradation. And of course if the protein isn't there it's not going to be able to function. And therefore that's a major way of controlling the gene expression. So we've talked about protein degradation before but just when I mentioned just a little bit related to this protein degradation usually occurs through labeling of ubiquity in which targets that protein for proteins um destruction or license zonal destruction. Um But then there's this other term that we haven't talked about specifically but this is called degraan and that's actually region of the protein that controls the proteins destruction. So for instance um this is an image looking at the presence of a Deborah and how it affects a protein present over time. So we have this protein, this is called the G. F. P protein and this is over time. So as it's as it's degrading, Let me back away here. So here's a Degraan. This is just going to be some kind of protein sequence or protein structure that's on the protein that marks it for degradation. And you can see that the G. F. P. With the degraan is actually being degraded significantly over time, whereas the protein without the degraan is still present and similar amounts to when it started. The day grins are just regions of a protein that control the proteins destruction and degradation. So that's protein regulation of gene expression. So now let's move on.