Transcription in Eukaryotes - Video Tutorials & Practice Problems
On a tight schedule?
Get a 10 bullets summary of the topic
1
concept
Eukaryotic Transcription
Video duration:
9m
Play a video:
Hi in this video we're gonna be talking about eukaryotic transcription. So eukaryotic transcription is more complex than pro periodic transcription and I don't think anyone's probably surprised about that. Of course it is. And the first way that it's different is through RNA plate races because there are a lot of different ones that transcribed RNA. And you carry out eukaryotic transcription that don't exist in procreative transcription. So you have RNA from Race 12 and three. There's a couple others four and five which I'm not gonna mention. But 12 and three are the main ones. Uh RNA from Race one does ribosomes. RNA. A. RNA polymerase too is messenger RNA. And so this is the one we're gonna be talking about for the most part and RNA polymerase three does T. R. N. A. Now they also do other RNA. There's various non coding RNA is that I'm not mentioning here but just in general this is the main the main RNA that's transcribed by each one of these. So because I think RNA polymerase three does certain types of R. R. N. A. They usually all do some kind of non coding RNA as well. But they're very specific with what they do and they don't transcribe the RNA. They shouldn't. And so the first thing you start with is transcription initiation and transcription initiation requires many different factors and these are generally proteins. And um the first set of factors that it requires are called general transcription factors and they're given fancy names. T. I to A. T. F. To B. T. F. Two D. Um they're given these fancy names, we're gonna talk about this one in a second but their general transcription factors. And so anytime transcription is occurring for transcription NG M. R. N. A, which is what we're talking about, messenger RNA, um they have to be there to initiate transcription. There are there every single time M. RNA is being transcribed. And what happens to them is there's a bunch of different ones. But essentially what they do is they bind to the eukaryotic promoter and this is promoter exactly the same as the pro chaotic promoter. Um It's a D. N. A sequence that initiate the initiation factors bind to its present upstream of the gene that's being transcribed. Now the eukaryotic promoters have different sequences than the pro chaotic promoter. So eukaryotic promoter, a very common one is called the top box. This is a sequence of T N. A. S around 30 base pairs upstream of where the transcription starts. And so the protein that binds this is the general transcription factor. Um You see it depending on your book, you may see it as T I two D. Or you may see it as the tata binding protein is the same thing and essentially it binds this sequence and recruits all the other general transcription factors that are necessary for transcription to be initiated. And so when all those factors are present, the G. Um the GTs that's what I'm supposed to say. General transcription factors bind to this promoter. And eventually when they're all there and transcriptions ready to start they recruit RNA polymerase too. And so this is called the pre initiation complex with all of the general transcription factors and RNA polymerase too. So when it has both of them that's the pre initiation complex. So here's an example. So here's a bunch of different factors. But because the G. The general transcription factors and RNA polymerase are present this would be the pre initiation complex that I mentioned before. And then transcription will go and eventually it will be released now after initiation begins transcription elongation begins. And how this happens is because the RNA polymerase to that controls um that is transcribing the M. R. N. A. Has a special pro a region on its protein. It has a tail on it. And this tale is called the car box C. Terminal domain. And so RNA polymerase has this little protein tail hanging off of it and we call it the C. T. D. And this is what controls its ability to elongate the transcript. So what happens is that the region on this tail can be phosphor related meaning that it gets phosphates. So what a phosphate is added to this tale that will activate the RNA Flynn raise and release it from the pre initiation complex and then it's free to go. So what happens is you kind of think of it as like a wind up car or toy. Right? So the RNA a RNA polymerase is there and the G. T. F. So the transcription factors wind that toy up and they do that by adding phosphates. So when the phosphates added it winds it once you know phosphates get added and it gets wound up and then eventually it gets so wound up so fast correlated it's released and so it's released from the transcription initiation complex and it then goes and it elongates that transcript. So once it's released once it's been wound up and phosphor related it will elongate the transcript. Now it keeps going it keeps going, it keeps going and it'll keep going indefinitely until transcription termination starts. Now for eukaryotic cells there's not really a specific sequence that triggers termination. Right? I said in pro carry optic transcription there were specific sequences called terminators that did it. But in eukaryotic transcription it doesn't really work like that. And often the RNA polymerase too will transcribe hundreds or even thousands of nuclear appetites past where it should have stopped past the coding sequence and eventually it will fall off right eventually sometimes there are sequences way downstream but essentially the RNA polymerase will eventually fall off. It'll receive some type of signal phosphor relation will get weak, it will fall off and this RNA processing has to occur after it's fallen off after the termination because now you have potentially thousands of nucleotides that shouldn't be there. So the RNA has to undergo processing after it's transcribed and we'll talk about this and its whole separate video. So here we have the RNA Plum race and now it has a phosphate on it. And this will release the RNA polymerase from this complex and it will go and transcribe until it falls off. Now a number of factors control transcription. So we've talked about promoters, we've talked about the generalized transcription factors but there's a lot of other factors that also control transcription. One of them is called an enhancer and this is going to help activate and enhance or speed up transcription. There's also silencers which do exactly what you think they would do. They repress it. And then we talked about generalized transcription factors but there's actually some genes have specific transcription factors and these at work to activate or repress only specific genes. And so if these specific transfer factor transcription factors aren't there with the generalized ones it won't work correctly. So that all these different factors and all these different levels of regulation that control the transcription. Now these factors we've always just sort of assumed that they're you know, directly next to the gene but that's actually not the case and they can be located near or far based to where transcription is starts. So there are things called cis acting elements and they're called cis acting elements. As long as they're found on the same chromosome. So these could be right next to the gene or they can be located almost our entire chromosome away. But as long as they're on the same chromosome, their cis acting elements. And then there are transacting elements that are so far away from the gene trans the transcription start site that they're actually founded other chromosomes. And you may say, how does that even work? And the reason is because we often think of chromosomes in this form, because that's how we see them in when cells are dividing. But actually most of the time chromosomes don't look like this. They look like this in the cell. There's all chromosomes and they're all like round up together and they're not in this form. And when it looks like this, you can very easily imagine how a portion of a gene on another chromosome to a transacting element may be close enough to the gene to initiate transcription uh to control transcription. And so this is an example of assists acting elements. So here we have an enhancer. It's pretty far away. Here's the promoter and here's the gene of interest. So you can see here's it's not labeled here. But this is our name. Memories write our name is being recruited. Here's some other factors, some transcription factors, some enhancers, potentially some suppressors that are coming on and this will actually can fold over and initiate transcription. Which is an interesting way that enhancers can work if they're very far away on the chromosome. Um, so that is eukaryotic transcription. So with that let's not move on.
2
Problem
Problem
Which of the following polymerases is responsible for transcribing mRNA in eukaryotes?
A
RNA polymerase I
B
RNA polymerase II
C
RNA polymerase III
D
RNA polymerase
3
Problem
Problem
Which of the following general transcription factors is responsible for binding to the TATA-Box
A
TFIIA
B
TFIIB
C
TFIID
D
TFIIH
4
Problem
Problem
Which of the following modifications occurs to the RNA polymerase tail in order to trigger it to elongate the transcript?
A
Methylation
B
Acetylation
C
Carboxylation
D
Phosphorylation
5
Problem
Problem
Which of the following regulatory mechanisms regulates transcription from a great distance away from the gene?
A
Silencers
B
Specific transcription factors
C
Enhancers
D
Promoters
Do you want more practice?
We have more practice problems on Transcription in Eukaryotes