Cell Nucleus

00:01 Alright, and we're on to the final topic in this whole notion of subcellular organization normal housekeeping and that's self-replication.

00:09 This is going to be really brief.

00:11 We're just gonna talk about some interesting elements that you need to be aware of. I'm not gonna get into genetics in a big, heavy way.

00:18 It's not my thing. I'm more of a cell biologist.

00:21 Okay, so, I've said enough.

00:24 Let's look at self-replication which is one of the final basic cell housekeeping functions.

00:29 We have to turn over the cell.

00:31 We have to duplicate it and we have to also regulate all the other things, one through seven.

00:37 How do we do that? So, remember, the molecular biologists view the cell how it's all nucleus and there's a little bit of cytoplasm.

00:45 Well, that's not exactly right obviously.

00:47 The nucleus has much, much more structure than it is shown here.

00:52 First of all, it's got a membrane.

00:55 In the membrane, the nuclear envelope is gonna be very important in terms of regulating the structure and function of all the genetic material that's contained within the nucleus.

01:08 If that membrane gets perturbed, we're gonna see that there are diseases associated with that.

01:12 So, there's an outer membrane, inner membrane and they are permeabilized poked full through with nuclear pores that allow material to get into the nucleus but also allow material liked messenger RNA and ribosomes to get out of the nucleus.

01:28 So, we have a kind of a two-way street through some rather large nuclear pores.

01:32 There are also ribosomes that are intimately associated with the nuclear membrane.

01:37 So, the chromatin's an important way for us to recognize whether a cell is active or inactive.

01:43 Come back to that in just a minute. And then, the nucleolus.

01:47 That little blob in the middle of the nucleus is also an important indicator of how active transcription is.

01:55 The nucleolus is the source of ribosomes and you have a bigger, more prominent nucleolus in a cell where you're saying, "Wow, a lot of ribosomes, a lot of protein synthesis, that's an active cell." And if it's a very small or inconspicuous nucleolus, we say, "Yeah, it's probably not too active." The chromatin as I'd mentioned is also an important indicator of how active a nucleus is.

02:15 If it's euchromatin, then, that material is open.

02:21 It's transcriptionally available to allow various factors to bind and start making messenger RNA.

02:29 So, we can recognize open chromatin or euchromatin.

02:33 It's transcriptionally active. In comparison, when it's condensed, all the necessary enzymes, transcription factors, all those things cannot get in.

02:41 And so, that's transcriptionally inactive.

02:44 So, when we have a small, condensed nucleus that's almost all heterochromatin, that's probably a very inactive cell.

02:51 On the other hand, if we have a cell that's got lots and lots of euchromatin, that's probably really going gangbusters and we use the chromatin pattern in the presence or absence of a nucleolus, in many cases, to decide whether something might or might not be malignant.

03:07 We'll come back to that.