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11. Cell Division

Organization of DNA in the Cell

11. Cell Division

Organization of DNA in the Cell

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1

concept

Organization of DNA in the Cell

6m

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so recall from our previous lesson video that before any cell can divide, it must first replicate or duplicate or make an extra copy of its d N A. And so how the DNA is organized in the cell is very important. And in this video we're going to introduce the organization of DNA in the cell and which will notices throughout this video. We're going to introduce a whole bunch of different terms and notice that the terms that link directly to the image down below are labeled with these letters, and we have letters A, B, C, D and E. And once again, these letters labeling specific terms are going to link directly to the letters that we have down below in our image. And so keep that in mind as we go through this video. And so the very first term that we're going to introduce here is a term called the genome, and the genome refers to the complete set of all of a cell's DNA. And all here is the key word. Now the genetic material is referring to molecules that determined the inherited traits of an organism, and usually when scientists use the term genetic material. They're referring to the D N A of the organism. Now, within a cell, the DNA is going to associate with proteins that air called his stones. And these his stone proteins are going to form units that air called nucleus zones. And so the nucleus OEMs themselves can be can be defined as units of eight, his stone proteins at the core with DNA wrapped around it. And so to start, to understand these terms, let's take a look at our image down below. And so we'll start here with term A the genetic material DNA. And so notice here, we're showing you an image of DNA as we've discussed it in our previous lesson. Videos. Ah, double stranded helix of nucleotides. As we see now within a cell. It turns out that the DNA is going to be organized into thes units called nucleus OEMs, and the nuclear ISMs form when DNA is wrapped around thes hissed own proteins. And so notice these little purple circles that you see throughout our Histon thes histon proteins. And the Histon proteins will organize into, uh, these units of eight Histon proteins. Andi, The Histon proteins formed the core of the nucleus zone and DNA will wrap itself around the hist own protein, almost like taking a core of ah, pencil or a pen. If that was the hist own core and taking a ah yarn and wrapping the yarn around the hiss stone protein. That's basically what the nuclear zone consists of histon proteins at the core with DNA wrapped around it. Now it turns out that within the cell, these nuclear zones can actually take different forms, depending on if the cell is actually in a non dividing state or if the cell is in a dividing state. And so when the cell is in a non dividing state when the cell is not dividing, it turns out that the DNA in the nucleus homes are going to be organized into what's known as chroma tin. And so Chroma tin represents loosely packed or coiled nuclear ISMs and non dividing cells. But when the cell is about to divide in a dividing cell, the nuclear zones take a different form, and they're no longer loosely packed or coiled. Instead, they're going to become tightly packed into what are known as chromosomes, and so crow. Metin refers to loosely packed or coiled nucleus homes in a non dividing cell and chromosomes is referring to tightly packed or highly condensed nucleus OEMs in a dividing self. And so let's take a look at our image down below to get a better idea of this. And so notice on the left hand side over here, what we're showing you is a non dividing cell. And so notice that within the nucleus of this non dividing cell when you zoom in here, the DNA is organized in this format here, where the genetic material, the DNA is wrapped around his stone proteins to form these nucleus homes and these nuclear zone sub units, these nuclear is, um, units here, uh, when the cells in a non dividing state it's going to be in a loosely coiled state called chroma eaten. And so over here, in the non dividing state, the DNA is in a crow Metin form, and the crow misinform because it's so loosely coiled. You can really think of a ball of yarn that is really loosely coiled and so notice that we have this loosely coiled ball of yarn here or bunch of yard. But notice that over here on the right hand side, what we have is the dividing cell and notice that the dividing so the DNA is going to condense. And so we have condensing DNA here, and the DNA condenses into highly condensed or tightly packed chromosomes. And so, really, this term chromosomes, you could think of a ball of yarn that is really, really tightly coiled, nicely wrapped around, unlike the ball of yarn that's over here. And so the term chroma 10 and chromosomes are both preferring to DNA wrapped around protein. And the difference is really that Crow Metin is going to be, um, or loose form of the DNA found in non dividing cells, whereas chromosomes are going to be mawr tightly coiled DNA that air found in dividing cells. And so this is going to be very, very important, this condensing of the DNA into chromosomes. It's going to be very important for moving the DNA around within a cell that is dividing, and so we'll get to talk a lot more about chromosomes and the dividing cell as we move forward in our course here. But for now, this here concludes our introduction to the organization of the DNA in the cell, 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.

2

Problem

Problem

A collection of DNA and associated proteins in a cell defines the term:
a) Sister Chromatids.
b) Centromere.
c) Chromatin.
d) Chromosome.

A

Sister Chromatids.

B

Centromere.

C

Chromatin.

D

Chromosome.

3

Problem

Problem

Choose the option that correctly lists the following genetic material in a dividing cell from smallest to largest.

A

DNA, Chromatin, Nucleosomes, Chromosomes.

B

Chromatin, Nucleosomes, Chromosomes, DNA.

C

DNA, Nucleosomes, Chromatin, Chromosomes.

D

Chromosomes, Chromatin, Nucleosomes, DNA.

4

concept

DNA Replication

5m

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in this video, we're going to briefly discuss how DNA replication produces replicated chromosomes. And so later in our course we're going to talk a lot more details and go way more in depth about this process of DNA replication. But in this video we're only going to lightly introduce DNA replication just enough to help you understand how it produces replicated chromosomes. And so first we need to recall from way back in some of our previous lesson videos that before a cell can actually divide. It's critical that the DNA must be replicated. Now this term replicated has a few synonyms that can be commonly used by your professors or in your textbook. And so the term replicated is synonymous with the term synthesized and or duplicated. And so DNA replication, DNA synthesis and DNA duplication all mean the same thing. And so we can say that this process of DNA replication is a process that produces an exact copy of all of the D. N. A. Inside of a cell. And so again this is critical for a cell to do before it actually divides. Because when a single cell divides into two separate cells, each of those cells needs a copy of the D. N. A. And that can only happen if DNA replication happens first. Now this process of DNA replication is going to convert unrepresented chromosomes or chromosomes that have not yet been replicated into replicated chromosomes or chromosomes that have gone through DNA replication. And so these replicated chromosomes that have gone through DNA replication are going to have two identical sister. Chroma tides. Now, the term sister here is really just used to imply that these chroma tides are identical to one another in terms of their D. N. A sequence. And the term chroma tied can really just be defined as half of a replicated chromosome. And the chroma tides are going to be joined to one another or one Chroma tide can be joined to another. Chroma tied at a region called the centrum ear. And so the central mere can really just be thought of as the waist position of the chromosome. And so we'll be able to see where the central here is in our image down below. And so if we take a look at our image, notice on the left hand side over here, what we're showing you is a single unrepresented chromosome. And so notice that this single un replicated chromosome kind of looks like a straight line uh here in this image and we can also think of a single unrepresented chromosome as just one chroma tied. Again, one chroma tide can be thought of as half of a replicated chromosome now notice this gray arrow here represents the process of DNA replication which is going to make an exact copy of this chromosome. And so after DNA replication, notice on the right hand side, what we have is a single replicated chromosome and so again, this replicated chromosome has gone through the process of DNA replication. And so what you'll notice is that our unrepresented chromosome again is right here highlighted. And with this replicated chromosome we still have that same unrepresented chromosome is pressed. However, you'll notice that the unrepresented chromosome has been replicated. So over here, what we have is another identical copy of the pink highlighted region. And so what we call these regions, Okay, we call this and this. We call them chroma tips. And so uh these two here we can say they are too identical chroma types. Or in other words, they are sister chroma tides. And what you'll notice is that this uh sister cremated and this sister chromatic are attached to each other at this one position right here that we call the centrum ear. And so again, the centrum ear is almost like the waist position of a chromosome where The two sister chromosomes will be joined. And so this is a critical information because we can we can tell if a chromosome has gone through DNA replication because if the chromosome uh somewhat looks like an X. As you see over here, then we know that it's gone through DNA replication. But if the chromosome does not look like an X and it looks more like a straight line, then we can say that it is an unrepresented chromosome that has not yet gone through DNA replication. And so that can be very helpful information to note as we move forward and talk more about cell division. But for now this year concludes our brief lesson on how DNA replication produces these replicated chromosomes, and we'll be able to get some practice as we move forward, so I'll see you all in our next video.

5

Problem

Problem

The structures labeled Y in the image below are called:

A

Centromeres.

B

Centrioles.

C

Sister chromatids.

D

Spindles.

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