Organization of DNA in the Cell - Video Tutorials & Practice Problems
On a tight schedule?
Get a 10 bullets summary of the topic
1
concept
Organization of DNA in the Cell
Video duration:
6m
Play a video:
Video transcript
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 DNA. 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 what you'll notice is 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 keyword. Now the genetic material is referring to molecules that determine the inherited traits of an organism, and usually when scientists use the term genetic material, they're referring to the DNA of the organism. Now within a cell, the DNA is going to associate with proteins that are called histones. And these histone proteins are going to form units that are called nucleosomes. And so the nucleosomes themselves can be can be defined as units of 8 histone 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. A double stranded helix of nucleotides as we see. Now within a cell, it turns out that the DNA is going to be organized into, these units called nucleosomes. And the nucleosomes form when DNA is wrapped around, these histone proteins. And so notice these little purple circles that you see throughout are histones, these histone proteins. And the histone proteins will organize into, these units of 8 histone proteins. And the 8 histone proteins form the core of the nucleosome, and DNA will wrap itself around the the histone protein, almost like taking, a core of a pencil or a pen if that was the histone core, and taking a, a yarn and wrapping the yarn around the histone protein. That's basically what the nucleosome consists of. Histone proteins at the core with DNA wrapped around it. Now, it turns out that within the cell, these nucleosomes, 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, the nucleosomes are going to be organized into what's known as chromatin. And so chromatin represents loosely packed or coiled nucleosomes and non dividing cells. But when the cell is about to divide in a dividing cell, the nucleosomes 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 chromatin refers to loosely packed or coiled nucleosomes in a non dividing cell. And chromosomes is referring to tightly packed or highly condensed nucleosomes in a dividing cell. 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 histone proteins to form these nucleosomes. And these nucleosome subunits, these nucleosome units here, when the cell is in a non dividing state, it's going to be in a loosely coiled state called chromatin. And so over here in the non dividing state, the DNA is in a chromatin form. And the chromatin form, 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 yarn. But notice that over here on the right hand side, what we have is the dividing cell. And notice that the dividing cell, 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 can 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 referring to DNA wrapped around protein. And the difference is really that chromatin is going to be a more loose form of the DNA, found in non dividing cells. Whereas chromosomes are going to be more tightly coiled, DNA that are found in dividing cells. And so this is going to be very, very important. This condensing of the DNA into chromosomes is 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
Video duration:
5m
Play a video:
Video transcript
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 DNA 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 2 separate cells each of those cells needs a copy of the DNA and that can only happen if DNA replication happens first. Now this process of DNA replication is going to convert unreplicated 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 2 identical sister chromatids. Now the term sister here is really just used to imply that these chromatids are identical to one another in terms of their DNA sequence. And the term chromatid can really just be defined as half of a replicated chromosome and the chromatids are going to be joined to one another or one chromatid can be joined to another chromatid at a region called the centromere. And so the centromere can really just be thought of as the waist position of the chromosome. And so we'll be able to see where the centromere 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 unreplicated chromosome and so, notice that this single unreplicated chromosome kind of looks like a straight line, here in this image. And we can also think of a single unreplicated chromosome as just one chromatid. Again, one chromatid 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 unreplicated chromosome again is right here highlighted and with this replicated chromosome we still have that same unreplicated chromosome as present. However, you'll notice that the unreplicated 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 chromatids and so, these 2 here we can say they are 2 identical chromatids or in other words, they are sister chromatids. And what you'll notice is that this sister chromatid and this sister chromatid are attached to each other at this one position right here that we call the centromere. And so again the centromere is, almost like the waist position of a chromosome where the 2 sister chromatids will be joined. And so, this is critical information because we can we can tell if a chromosome has gone through DNA replication because if the chromosome, 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 unreplicated 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 here 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: