Eukaryotic Chromatin Modifications

in this video, we're going to begin our lesson on Eukaryotic chromosome modifications. And so eukaryotes can regulate gene expression by modifying the structure of their chroma tin. And so recall from our previous lesson videos that Crow Mountain are loosely packed or uh, loosely coiled nuclear zones, which is basically just d n a wrapped around units of eight histone proteins. And so, if you don't recall this, then make sure to go back and watch those older lesson videos on D N A. Before you continue here. Now, modifications to histone proteins or modifications to the DNA sequence itself can actually impact uh, the transcription process. And so, uh, histone modifications and D n A sequence modifications are made to control transcription. But these modifications are taking place at the chromosome level, affecting the histone proteins or the D N. A sequence. And really this leads to two different types of chroma tin. It leads to hetero chrome button, and also it leads to you Crow Metin, now hetero chrome button, is going to be a condensed region of the genome with really, really low transcription activity, and so hetero chrome button is not going to be transcribed and you, Crow Metin is basically the opposite is a lightly packed region of the genome with high transcription activity and histone and DNA modifications. And so, if we take a look at our image down below, uh, we can distinguish between Hetero Crow Mountain and Ukraine Martin. And so again, over here on the left hand side, we have this miniature version of our map of the lesson. And again, we're starting off with chromatic modifications, which is going to take place in the nucleus sense. That is where the Crow Mountain is found, and so hetero chrome button is basically like turning off the light switch. It turns off transcription and turns off genes, and so it's going to represent really, really tightly packed Um uh, chromatic heteronormative is super super tightly packed, and that's going to have really, really low transcription all activity. And this is simply because the transcription machinery, like RNA preliminaries and things of that nature will not be able to fit in access the DNA that it needs to access because it's so tightly packed and so hetero. Crompton. This tightly packed D N. A is a way to lower transcription activity and turn off genes a form of regulation. Now you chrome button, on the other hand, is a way to turn on the light switch to turn on genes so that transcription activity is high. And so notice that over here the chrome button is much more loosely packed. And because it is loosely packed, it's going to have high transcription ALS activity. And so you can see that the transcription machinery like Arnie Proliferates, for example, is capable of accessing the DNA that needs to be transcribed. And so because the D. N A is loosely packed, it's going to have high transcription of activity, and that is a way of turning on the genes. And so this year concludes our brief introduction to Eukaryotic chromosome modifications. But as we move forward, we're going to continue to talk about specific modifications that can take place that will lead to either hetero Crow Mountain or you crow Martin. Uh, and so I'll see you all in our next video

In this video, we're going to introduce a specific type of chromatic modification, which is his stone assimilation. And so his stone proteins that are found within nucleus OEMs of chrome autumn they actually contain a long polyp peptide tail. And this long polyp peptide tail that extends off the histone proteins can actually be chemically modified by cellular enzymes. And the most common modification to the histone protein tales is assimilation. And assimilation is just the process of the addition of an acetyl group, and you can see down below in our image. And acetyl group is just a specific type of functional group, the one that you see right here and in our image down below. We're going to represent assimilation and acetyl groups by using a star symbol to represent the assimilation. Now his stone assimilation actually impacts the chromosome structure because what it does is it loosens the chromosome structure, and that helps the chromosome take on a you crow Metin formation, making the D N A accessible to RNA polymerase and allowing that DNA to be transcribed at a high rate. And so in our example down below, noticed that we're focusing on how histone assimilation loosens the chromosome structure forming you chrome button. And so if we take a look at our image down below again on the left hand side, we're showing you are miniature version of the map. And, uh, you can see that chromatic modifications, which include his stone assimilation, is going to take place within the nucleus of the eukaryotic cell. And so here, what we're showing you is the chrome eaten in a hetero chroma to inform where the nucleus OEMs are really tightly packed together. But notice that extending off of each of these his stones are these little tails and these are called the histone tails. And these histone tails are capable of being modified by cellular enzymes. And so, in this formation over here, the hetero chrome button, the D. N A. Is basically in an off state, and it's not going to be transcribed very much. However, through a simulation which is represented by this arrow right here, assimilation can help turn the d n a into an on confirmation the chromosome structure into an on confirmation because it changes the crow Metin two au chromosome state where it is more loose, and, uh, the D N A. Is more accessible to RNA polymerase and more accessible to transcription. And so you can see the little stars here on the histone tails represents the assimilation, and the assimilation again is going. It's going to be a way to help, uh, allow for transcription to occur. Now, removal of the acetyl groups in a process called D assimilation is actually going to result in the opposite. It's going to result in tight packing of the chromosome structure, basically reverting the chroma team back to the hetero chromosome state. And so on the left. Over here we have the hetero chrome button, which we talked about in our last lesson video. And over here on the right, we have the You Crow Martin and notice that assimilation will help promote a U chromosome state where transcription is more active and then D assimilation is going to promote a hetero chromosome state where the D. N A. Is not going to be transcribed as much. And so his stone assimilation is a chroma tin modification that can occur to help regulate gene expression. And so we'll be able to get some practice applying this as we move forward in our course. So I'll see you all in our next video

in this video, we're going to introduce another type of eukaryotic chromosome modification, which is DNA methylation. And so, in addition to histone modifications like his stone assimilation and histone d oscillation, the actual DNA sequence, not just the headstones can also be chemically modified to regulate transcription. And the most common DNA modification is methylation and methylation is really just the process of adding a methyl group or a CH three group, uh, to another substance. And typically, when it comes to DNA methylation, it turns out that the nucleotides side a scene are the ones that are most susceptible to methylation. And so the cytosine residues are the ones that are going to be methylated. Now, DNA methylation is a way to prevent transcription by blocking RNA. Polymerase is access to the promoter, and so DNA methylation will turn off a gene or turn off transcription. And so, in our image down below, we can see in our example that methylation of cytosine nucleotides is going to block transcription and turn off a gene. And so what you'll notice is over here on the left hand side, notice that we have a C dilated histone modifications. The stars the Green stars from our last lesson video represent assimilation and assimilation we know is going to turn on genes. So jeans are going to be turned on by assimilation because the DNA is going to take a U chromosome state and that is going to promote transcription. And so the genes turned on by assimilation by promoting transcription. And so the RNA preliminaries will be able to bind to this open and available D N A. And we'll be able to transcribe genes in this DNA that is available here. And so this is a way of turning on the gene, however, however methylation of specific cytosine residues, cytosine, nucleotides, uh, methylation of cytosine, which methylation is being adding a ch three groups to the molecule. It's going to be represented using one of these red Star shapes, uh, noticed that the D N A itself can actually be methylated. And so this modification occurs to the DNA sequence directly not to the headstones. And so the DNA can be methylated, and the DNA methylation is a way to turn the gene off. The genes are going to be turned off and notice that the methylation is blocking RNA preliminaries from binding to the DNA. And so the RNA preliminaries will not be able to transcribe the D. N. A. And the gene is being turned off through methylation of cytosine nucleotides. And so what you can see here is that through assimilation and methylation, the eukaryotic organisms have a very, uh, complex way to be able to regulate their genes, turn the jeans off and turn the jeans on, depending on the type of modification that's made. And so this here concludes our introduction to DNA methylation, 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.