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13. Gene Regulation in Eukaryotes

Overview of Eukaryotic Gene Regulation


Review of Regulation

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Hi in this video we're gonna be talking about an overview of eukaryotic gene regulation. So the majority of the regulatory ability of the eukaryotic genome. We've already talked about this is because gene expression is regulated at every single step from transcription to translation. So this is more of just a review of the things that we've mainly already talked about when we talked about transcription and translation. But I just want to put it here because I do want to point out that these are actual ways that gene expression is controlled and not just things that you know happen occasionally because there is a purpose to all of these different mechanisms because they regulate gene expression and controlled what genes are being expressed and therefore the phenotype of the organism. So um the first thing is that we have transcription initiation and remember that initiation is controlled through several factors. You have an idea other than the ones mentioned here anything that you might think of right promoters, They have to be, you know, the promoter sequences recruit proteins. Those proteins are called transcription factors and there's both specialized and generalized and both of these um can activate or suppress transcription. You also have these other DNA sequences, enhancers, activators, silencers. And these are all DNA sequences that are found either before the gene or uh after the gene starts. And they all work together to cause a huge amount of transcription or a small amount of transcription or no transcription at all. And so this is one big way that gene expression is regulated. Now one thing that we haven't talked about yet is how these proteins that are specifically transcription factors but there could be other proteins as well bind to the D. N. A. And it's mentioned here in this chapter. So I want to throw it in now. And this is because these transcription regulatory factors that bind to D. N. A. Have DNA binding motifs. So these are protein motifs on the factors binding the D. N. A. That allow them to bind to D. N. A. And there's four main ones. You have helix turn helix zinc finger losing zipper and helix loop helix. So helix turn helix is exactly what it sounds like. So you have to heal these. These are alpha helix is remember back to remember to the protein secondary structure are alpha helix is. So there are two alpha jealousies and they're separated by a turn. That's why it's called helix turn helix. You have zinc finger. So this is a structure that binds ink and looks like a finger. Not this hard to remember. You have loosened zipper, it's a dime er right zipper that has two rows of teeth and a zipper. So this is a protein that has two parts to the dime. Er and it zips together at lucy's those diamonds come together like a zipper at the loosens. And then you have helix loop helix which is the same almost as helix turn helix. Except they're connected by a loop instead of a turn. So here's examples of these you have. So the green here, this is the D. N. A. So the green is the helix. It's hard to tell here but these are helix. Loop helix is you have your zinc finger, here's the zinc. People say the structure looks like a finger. I personally have a hard time seeing it but that's kind of what they say. I mean I guess this part here looks like a finger. You have your zipper which I think looks much more like a zipper right your blue and your green proteins coming together. And then you have your helix loop helix with the D. N. A. Here and these here these are connected through a loop. So that is how these proteins bind to D. N. A. And regulate transcription. But gene expression is also regulated through many steps involving RNA processing, stability and translation. So some of these things that we've talked about are things like RNA interference and this is the process that uses the small non coding RNA is either micro RNA. S. Or S. I. R. N. A. S. And this degrades certain transcripts. Most of you will have a video on RNA interference of your book goes over it. Some of you won't. Um And if it doesn't don't worry about it but RNA interference like I said it's a process that regulates gene expression by degrading um transcripts using RNA. Then we have RNA processing which everyone will have heard about from me. And these are things like the five prime cap, the three prime poly A tail. And the most important one is splicing. Because there is a form called alternative splicing where different Exxon combinations are put together. And this alternative splicing can create multiple different protein Aisa forms. And this ice a form will result in potentially a different phenotype depending on the protein Ice A form. So it's all the same protein. It all comes from the same gene. But the diff different combinations of Exxon's and the different order of Exxon's produces these different forms of the same protein called an ice A form and that can result in different phenotype. So the best example of this that is mentioned in your books is the fruit fly sex determination. Right. And it's actually controlled through alternative splicing. So what controls whether a fruit fly is a male or female? So what? So what controls that is actually a ratio called the X. To a ratio. And that's the ratio of X chromosomes to autism all chromosomes. So if you have a ratio of one meaning that the number of X chromosomes is the same as number of autism all chromosomes. So 11. Right? So if the ratio is one what happens is that this X. L. Gene becomes activated? So this is the ratios one. When this is activated, What happens is the T. R. A. Is spliced. So here we're talking about splicing, right? And when this is spliced, this activates another gene, D. S. X. And this is the important gene here and so when the T R. A T R A gene is spliced then the D. S. X. Protein has a female specific splicing. So that's kind of this is the image of the word thing. Now if the ratio is 0.5 right meaning that there are more autism of chromosomes than X chromosomes, then what happens is the excel gene is inhibited and that means that no tiara is spliced. And if no T. R. A. S. Life is what you get is you still get D. S. X. But you get a different form. So the male specific form is produced. And so the example of D. S. X. And that splicing is an example of alternative splicing. Because this pathway results in the female specific splicing of this D. S. X. And this pathway results in the mail specific splicing of D. S. X. And those to result in the different sexes of the fruit flies. So it's super important. And then finally um M RNA degradation happens whether something went wrong with transcription whether the cell isn't producing enough protein because of whatever reason if the you know some M. R. N. A. S. Have very short half lives meaning that they're degraded very quickly. And so this is also a super great way of regulating protein production because if you degrade the M. RNA it won't produce protein. So if you need to regulate gene expression by preventing the protein you can degrade the cell, can degrade the M. R. N. A. So that's a great way. So here's an example of alternative splicing. So here's D. N. A. R. N. A. You have your exxons, there's five of them all different colors. When you do transcription to get to R. N. A. Those are all kept. Then you go undergo splicing and you can see there's many different forms that this can have. You can have all five of them in order. You can cut out one. So three here is missing. Um And here's four missing. You can actually also not shown here but you can recombine them. Right? So 13245. That's also another way to do alternative splicing. And so you can see here that if you look at the protein that's created from these, they look different and these are all protein ice A forms that term I use before because it's the same protein. Right? I mean this is the same sequence. It's the same gene representing the same protein but they're protein Aisa forms because these proteins look different and they can have different functions. And that obviously I mean for uh fruit flies that determines their you know sex differentiation. Having a protein, the D. S. X. Protein actually result in different alternative splicing forms. So that is sort of a review of some of the concepts that we've talked about and how they specifically affect gene expression. So with that, let's now move on.

Which of the following is NOT a DNA binding motif?


Drosophilia sex determination is controlled through which of the following mechanisms?


Gene regulation in eukaryotes only occurs during the transcription stage of gene expression.