Chromosomes, chromatids and chromatin (video)

Video transcript

Before I dive into the mechanics of how cells divide, I think it could be useful to talk a little bite about a lot of the vocabulary that surrounds DNA. There ‘s a lot of words and some of them kind of voice like each early, but they can be very confusing. So the beginning few I ‘d like to talk about is barely about how DNA either generates more deoxyribonucleic acid, makes copies of itself, or how it basically makes proteins, and we ‘ve talked about this in the DNA video. So let ‘s say I have a little — I ‘m just going to draw a small section of DNA. I have an A, a G, a T, let ‘s say I have two T ‘s and then I have two C ‘s. Just some small section. It keeps going. And, of naturally, it’s a double coil. It has its equate bases. Let me do that in this color. So A corresponds to T, G with C, it forms hydrogen bonds with C, T with A, T with A, C with G, C with G. And then, of course, it merely keeps going on in that commission. So there ‘s a copulate of different processes that this deoxyribonucleic acid has to do. One is when you ‘re good dealing with your torso cells and you need to make more versions of your clamber cells, your deoxyribonucleic acid has to copy itself, and this process is called replication. You ‘re replicating the deoxyribonucleic acid. So let me do rejoinder. So how can this deoxyribonucleic acid replicate itself ? And this is one of the beautiful things about how DNA is structured. Replication. So I ‘m doing a gross oversimplification, but the idea is these two strands separate, and it does n’t happen on its own. It ‘s facilitated by a bunch of proteins and enzymes, but I ‘ll talk about the details of the microbiology in a future video recording. So these guys separate from each other. Let me put it up here. They separate from each other. Let me take the early guy. Too big. That guy looks something like that. They separate from each other, and then once they ‘ve separated from each other, what could happen ? Let me delete some of that thrust over hera. Delete that stuff right there. So you have this double helix. They were all connected. They ‘re base pairs. immediately, they separate from each early. now once they separate, what can each of these do ? They can now become the template for each other. If this guy is sitting by himself, now all of a sudden, a thymine base might come and join proper here, so these nucleotides will start lining up. So you ‘ll have a thymine and a cytosine, and then an adenine, adenine, guanine, guanine, and it ‘ll keep happening. And then on this other share, this other greens fibril that was once attached to this blue strand, the same matter will happen. You have an adenine, a guanine, thymine, thymine, cytosine, cytosine. So what fair happened ? By separating and then precisely attracting their complementary color bases, we merely duplicated this atom, right ? We ‘ll do the microbiology of it in the future, but this is precisely to get the estimate. This is how the DNA makes copies of itself. And specially when we talk about mitosis and meiosis, I might say, oh, this is the stage where the reproduction has occurred. now, the other thing that you ‘ll hear a lot, and I talked about this in the DNA video, is transcription. In the DNA television, I did n’t focus much on how does DNA duplicate itself, but one of the beautiful things about this double coil design is it very is that easy to duplicate itself. You just split the two strips, the two helices, and then they basically become a template for the other one, and then you have a duplicate. now, transcription is what needs to occur for this DNA finally to turn into proteins, but recording is the intermediate step. It ‘s the step where you go from deoxyribonucleic acid to mRNA. And then that messenger rna leaves the nucleus of the cell and goes out to the ribosomes, and I’ll spill about that in a second. So we can do the lapp thing. so this guy, once again during transcription, will besides split apart. So that was one separate there and then the other split is justly there. And actually, possibly it makes more common sense precisely to do one-half of it, so let me delete that. Let ‘s say that we ‘re barely going to transcribe the greens side right here. Let me erase all this thrust correct — nope, ill-timed coloring material. Let me erase this gorge right here. now, what happens is rather of having deoxyribonucleic acidic nucleotides pair up with this deoxyribonucleic acid strand, you have ribonucleic acid, or RNA pair up with this. And I ‘ll do RNA in magneta. So the RNA will pair up with it. And thus thymine on the DNA side will pair up with adenine. Guanine, now, when we talk about RNA, alternatively of thymine, we have uracil, uracil, cytosine, cytosine, and it barely keeps going. This is messenger rna. now, this separates. That messenger rna separates, and it leaves the nucleus. It leaves the nucleus, and then you have translation. That is going from the messenger rna to — you remember in the DNA video recording, I had the little transfer rna. The transfer RNA were kind of the trucks that drove up the amino acids to the messenger rna, and this all occurs inside these parts of the cell called the ribosome. But the translation is basically going from the messenger rna to the proteins, and we saw how that happened. You have this guy — let me make a transcript here. Let me actually copy the whole thing. This ridicule separates, leaves the nucleus, and then you had those little transfer rna trucks that basically drive up. So possibly I have some transfer rna. Let ‘s see, adenine, adenine, guanine, and guanine. This is transfer rna. That ‘s a codon. A codon has three base pairs, and attached to it, it has some amino acerb. And then you have some other piece of transfer rna. Let ‘s say it ‘s a uracil, cytosine, adenine. And attached to that, it has a different amino acid. then the amino acids attach to each early, and then they form this long chain of amino acids, which is a protein, and the proteins form these wyrd and complicate shapes. so fair to kind of make certain you understand, then if we start with DNA, and we ‘re basically making copies of deoxyribonucleic acid, this is replica. You ‘re replicating the deoxyribonucleic acid. now, if you ‘re starting with DNA and you are creating messenger rna from the DNA template, this is arrangement. You are transcribing the data from one form to another : transcription. now, when the messenger rna leaves the lens nucleus of the cell, and I ‘ve talked — well, let me just draw a cellular telephone fair to hit the point home, if this is a unharmed cellular telephone, and we ‘ll do the social organization of a cell in the future. If that ‘s the whole cell, the nucleus is the center. That ‘s where all the DNA is sitting in there, and all of the rejoinder and the transcription occurs in here, but then the messenger rna leaves the cell, and then inside the ribosomes, which we ‘ll talk about more in the future, you have translation occur and the proteins get formed. so messenger rna to protein is translation. You ‘re translating from the familial code, so to speak, to the protein code. So this is translation. So these are fair good words to make certain you get clear and make sure you ‘re using the right son when you ‘re talking about the different processes. nowadays, the early part of the vocabulary of DNA, which, when I first gear learned it, I found enormously confuse, are the words chromosome. I ‘ll write them down hera because you can already appreciate how confusing they are : chromosome, chromatin and chromatid. So a chromosome, we already talked about. You can have DNA. You can have a fibril of DNA. That ‘s a double helix. This chain, if I were to zoom in, is actually two unlike helices, and, of run, they have their base pairs joined up. I ‘ll fair draw some base pairs joined up like that. so I want to be clear, when I draw this little green pipeline here, it ‘s actually a double coil. now, that double helix gets wrapped around proteins that are called histones. So let ‘s say it gets wrapped like there, and it gets wrapped around like that, and it gets wrapped around like that, and you have here these things called histones, which are these proteins. now, this structure, when you talk about the deoxyribonucleic acid in combination with the proteins that kind of give it structure and then these proteins are actually wrapped around more and more, and finally, depending on what stagecoach we are in the cell ‘s animation, you have different structures. But when you talk about the nucleic acidic, which is the deoxyribonucleic acid, and you combine that with the proteins, you ‘re talking about the chromatin. So this is deoxyribonucleic acid plus — you can view it as morphologic proteins that give the DNA its supreme headquarters allied powers europe. And the mind, chromatin was first used — because when people look at a cell, every clock time I ‘ve drawn these cell nucleuses so far, I ‘ve drawn these very well defined — I ‘ll use the discussion. So let ‘s say this is a cell ‘s nucleus. I ‘ve been drawing identical well-defined structures hera. So that ‘s one, and then this could be another one, maybe it ‘s shorter, and then it has its homologous chromosome. So I ‘ve been drawing these chromosomes, right ? And each of these chromosomes I did in the last video are basically these farseeing structures of DNA, long chains of DNA kind of wrap tightly around each other. So when I drew it like that, if we zoomed in, you ‘d see one fibril and it ‘s actually good wrapped around itself like this. And then its homologous chromosome — and remember, in the variation television, I talked about the homologous chromosome that basically codes for the same genes but has a different interpretation. If the blue came from the dad, the red came from the ma, but it ‘s coding for basically the same genes. therefore when we talk about this one chain, let ‘s say this one chain that I got from my dad of deoxyribonucleic acid in this structure, we refer to that as a chromosome. now, if we refer generally — and I want to be acquit hera. DNA lone takes this form at sealed stages of its life when it ‘s actually replicating itself — not when it ‘s replicating. Before the cell can divide, DNA takes this very well-defined human body. Most of the cell ‘s life, when the deoxyribonucleic acid is actually doing its exercise, when it ‘s actually creating proteins or proteins are being basically transcribed and translated from the deoxyribonucleic acid, the deoxyribonucleic acid isn’t all bundled up like this. Because if it was bundled up like, it would be very hard for the replication and the transcription machinery to get onto the deoxyribonucleic acid and make the proteins and do whatever else. Normally, DNA — let me draw that like lens nucleus. normally, you ca n’t evening see it with a normal light microscope. It ‘s so slender that the DNA strand is good wholly separated around the cell. I ‘m drawing it here so you can try to — possibly the early one is like this, right ? And then you have that shorter strand that ‘s like this. And so you ca n’t even see it. It ‘s not in this well-defined structure. This is the way it normally is. And they have the other brusque ground that ‘s like that. So you would equitable see this kind of big mess of a combination of DNA and proteins, and this is what people basically refer to as chromatin. So the words can be very ambiguous and very confusing, but the general usage is when you ‘re talking about the chiseled one chain of deoxyribonucleic acid in this kind of well-defined social organization, that is a chromosome. Chromatin can either refer to kind of the structure of the chromosome, the combination of the deoxyribonucleic acid and the proteins that give the structure, or it can refer to this whole mess of multiple chromosomes of which you have all of this deoxyribonucleic acid from multiple chromosomes and all the proteins all jumbled together. so I just want to make that clear. now, then the following word is, well, what is this chromatid thing ? What is this chromatid thing ? actually, good in case I did n’t, I do n’t remember if I labeled these. These proteins that give structure to the chromatin or that make up the chromatin or that yield social organization to the chromosome, they’re called histones. And there are multiple types that give structure at different levels, and we’ll do that in more detail. So what ‘s a chromatid ? When deoxyribonucleic acid replicates — so let ‘s say that was my deoxyribonucleic acid before, justly ? When it ‘s equitable in its normal state, I have one version from my dad, one interpretation from my ma. now, let ‘s say it replicates. So my version from my dad, at first base it ‘s like this. It ‘s a boastfully strand of DNA. It creates another version of itself that is identical, if the machinery worked properly, and so that identical piece will look like this. And they actually are initially attached to each other. They ‘re attached to each other at a point called the centromere. now, tied though I have two strands here, they ‘re now attached. When I have these two strands that contain the claim — thus I have this fibril right here, and then I have — well, let me actually draw it a different way. I could draw it multiple different ways. I could say this is one maroon hera and then I have another strand here. nowadays, I have two copies. They ‘re coding for the demand same DNA. They ‘re identical. I hush call this a chromosome. This wholly matter is still called a chromosome, but now each individual copy is called a chromatid. So that ‘s one chromatid and this is another chromatid. sometimes they ‘ll call them sister chromatids. possibly they should call them twin chromatids because they have the like genetic information. so this chromosome has two chromatids. immediately, before the replication occurred or the deoxyribonucleic acid duplicated itself, you could say that this chromosome right here, this chromosome like a beget, has one chromatid. You could call it a chromatid, although that tends to not be the convention. people start talking about chromatids once you have two of them in a chromosome. And we ‘ll learn in mitosis and litotes, these two chromatids separate, and once they separate, that same strand of deoxyribonucleic acid that you once called a chromatid, you now call them individually chromosomes. So that ‘s one of them, and then you have another one that possibly gets separated in this guidance. Let me circle that one with the green. therefore this one might move away like that, and the one that I circled in the orange might move away like this. now, once they separate and they ‘re no long connected by the centromere, now what we in the first place called as one chromosome with two chromatids, you will now refer to as two separate chromosomes. Or you could say immediately you have two separate chromosomes, each made up of one chromatid. So hopefully, that clears up a little bite some of this slang around DNA. I always found it quite confusing. But it ‘ll be a utilitarian joyride when we start going into mitosis and meiosis, and I start saying, oh, the chromosomes become chromatids. And you ‘ll say, like, wait, how did one chromosome become two chromosomes ? And how did a chromatid become a chromosome ? And it all barely revolves around the vocabulary. I would have picked different vocabulary than calling this a chromosome and calling each of these individually chromosomes, but that’s the manner we have decided to name them. actually, just in event you’re curious, you ‘re probably think, where does this bible chromo come ? I do n’t know if you know erstwhile Kodak film was called chromo discolor. And chromo basically relates to color. I think it comes from the greek word actually for color. It got that parole because when people beginning started looking in the core of a cell, they would apply dye, and these things that we call chromosomes would take up the dye so that we could see it well with a light microscope. And some comes from human body for body, so you could kind of view it as colored body, so that ‘s why they call it a chromsome. So chromatin besides will take up — well, I wo n’t go into all of that ampere well. But hopefully, that clears a little bit this solid chromatid, chromosome, chromatin debate, and we ‘re well furnished now to study mitosis and meiosis.

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