In this video, we're going to begin our lesson on eukaryotic chromatin modifications. And so eukaryotes can regulate gene expression by modifying the structure of their chromatin. And so recall from our previous lesson videos that chromatin are loosely packed or, loosely coiled nucleosomes, which is basically just DNA wrapped around units of 8 histone proteins. And so if you don't recall this, then make sure to go back and watch those older lesson videos on DNA before you continue here. Now modifications can actually impact, the transcription process. And so, histone modifications and DNA sequence modifications are made to control transcription, but these modifications are taking place at the chromatin level affecting the histone proteins or the DNA sequence. And really this leads to two different types of chromatin. It leads to heterochromatin and also it leads to euchromatin. Now heterochromatin is going to be a condensed region of the genome with really really low transcriptional activity. And so heterochromatin is not going to be transcribed. And euchromatin is basically the opposite, it is a lightly packed region of the genome with high transcriptional activity and histone and DNA modifications. And so if we take a look at our image down below, we can distinguish between heterochromatin and euchromatin. 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 chromatin modifications, which is going to take place in the nucleus since that is where the chromatin is found. And so heterochromatin is basically like turning off the light switch. It turns off transcription. It turns off genes. And so it's going to represent really really tightly packed, chromatin, heterochromatin, super super tightly packed and that's gonna have really really low transcriptional activity. And this is simply because the transcriptional machinery, like RNA polymerase and things of that nature, will not be able to fit and access the DNA that it needs to access because it's so tightly packed. And so heterochromatin, this tightly packed DNA, is a way to lower transcriptional activity and turn off genes, a form of regulation. Now euchromatin on the other hand is a way to turn on the light switch, to turn on genes so that transcriptional activity is high. And so notice that over here, the chromatin is much more loosely packed. And because it is loosely packed, it's going to have high transcriptional activity. And so you can see that the transcriptional machinery, like RNA polymerase, for example, is capable of accessing the DNA that needs to be transcribed. And so because the DNA is loosely packed, it's gonna have high transcriptional activity and that is a way of turning on the genes. And so, this here concludes our brief introduction to eukaryotic chromatin modifications, but as we move forward, we're gonna continue to talk about specific modifications that can take place that will lead to either heterochromatin or euchromatin. And so I'll see you all in our next video.