Prática de Shadowing: Mitosis: Splitting Up is Complicated - Crash Course Biology #12 - Aprenda a falar inglês com vídeo
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146 frases
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Now check this out.
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Ha, cool huh?
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I bet you wish you could do this.
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Have a clone, clean up around the apartment for you, go to class, maybe take your mom out to dinner on her birthday.
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Well, you can't do that, and actually there are some really good reasons why you can't do that.
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We're gonna talk about those in the next episode.
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But you know what can clone themselves?
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Your cells.
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Like almost every single one of them, and in fact, they're doing it right now.
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For any creature bigger than a single -celled organism, all of life stems from cells' ability to reproduce themselves
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because that's what allows organisms to develop and grow and heal and keep from dying for as long as possible.
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This particular kind of cell division is called mitosis and it's responsible for a whole lot of your body's key functions.
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If you get it cut, your body needs to make new cells.
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Mitosis.
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Have too much to drink?
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Damage your liver?
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You gotta replace those cells.
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Mitosis.
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Tumor growing in your spine?
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Unfortunately, again, mitosis.
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While you go from a seven pound baby to a 70 pound child, it's not your cells that are increasing in mass,
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you're just getting more of them over and over and over again.
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That's mitosis.
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This process is so central to your life that it will take place in your body, over your lifetime, about 10 quadrillion times.
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That's 10 ,000 billion times.
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Like all split ups, it's not easy.
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It's gonna maybe be a little bit messy.
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There's a lot of drama and it can take a surprisingly long amount of time
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But trust me after we're done with it.
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We'll all be better off
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So you are made of trillions of cells just like giraffes
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and redwood trees and remember that inside each cell there's a nucleus
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that stores your DNA which contains all of the instructions on how to build you.
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That DNA is organized into chromosomes, and as we've mentioned before, in your body cells, or somatic cells, you have 46 chromosomes grouped into 23 pairs.
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One in each pair is from your mom, and the other one is from your dad.
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Cells with all 46 chromosomes are called diploid cells because they have two sets each, and that's what we're focusing on today.
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You also have haploid cells that have half as many chromosomes as 23.
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And those are your sex cells, they're produced in an equally fantastic process called meiosis, which we'll be talking about in the next episode.
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But for now, the main thing to remember about mitosis is
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that it allows one cell with 46 chromosomes to split into two cells that are genetically identical,
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each with 46 chromosomes, all in order to keep the party of life going.
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Now the nucleus in your cell controls everything that goes on in the cell, it has all the instructions necessary for making the cell survive,
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so you don't need to duplicate the whole cell.
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All you need to do is duplicate the DNA, get it wrapped up, and then if you have two separate pockets of DNA,
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that's all you need to have two new cells.
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Mitosis takes place in a series of discrete stages called prophase, metaphase, anaphase, and telophase.
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And you could just say that over and over again and let it sink into your head.
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And part of what's, you know, really amazing about this whole process is that while we know what these stages are,
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we don't always know the underlying mechanisms that make all of them happen.
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And this is part of science.
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Science isn't like all the stuff we know, it's how we're trying to figure all this stuff out.
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Consider it job security, if you ever want to be a biologist, there is a lot of stuff that future biologists have to still figure out.
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And this is one of them.
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Alright, let's get our clone on.
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So most of their lives, cells hang out in this limbo period called interphase, which means they're in between episodes of mitosis.
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Mostly growing and working and doing all the stuff that makes them useful to us.
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During interphase, the long strings of DNA are loosely coiled and messy, like that dust bunny of dog fur and laundry lint under your bed.
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That mess of DNA is called chromatin.
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But as the mitosis process begins to gear up, lots of things start happening in the cell to get ready for the big division.
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One of the more important things that happens is
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that this little set of protein cylinders next to the nucleus called the centrosome duplicates itself.
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We're gonna have to move a lot of stuff around in the nucleus, and that's gonna be regulated by these centrosomes.
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The other thing that happens is that all of the DNA begins to replicate itself too, giving the cell two copies of every strand of DNA.
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To brush up on how DNA replicates itself like this, check out this episode and then come on back.
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Now the cell enters the first phase, or the prophase, when that mess of chromatin condenses
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and coils up on itself to produce thick strands of DNA wrapped around proteins.
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Those, my friends, are your chromosomes.
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Instead of dust bunnies, the DNA is starting to look a little bit more like dreadlocks.
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And the duplicates that have been made don't just float around freely.
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They stay attached to the original, and together they look like little X's.
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These are called the chromatids, and one copy is the left legging arm of the X, and the other copy is the right legging arm.
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Where they meet in the middle is called the centromere.
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Just so you know, these X's are also called chromosomes, sometimes double chromosomes or double -stranded chromosomes,
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and when the chromatids separate.. they're considered individual chromosomes too.
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Now while the chromosomes are forming, the nuclear envelope gets out of the way by like, completely disintegrating.
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And the centrosomes then peel away from the nucleus, start heading to the opposite ends of the cell.
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As they go, they leave behind a wide trail of protein ropes called microtubules, running from one centrosome to the other.
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You might recall from our anatomy of the animal cell, that microtubules help provide a kind of structure to the cell.
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This is exactly what they're doing here.
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Now we reach the metaphase, which literally means after phase, and it's the longest phase of mitosis that can take up to 20 minutes.
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During the metaphase, the chromosomes attach to those ropey microtubules right in the middle at their centromeres.
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The chromosomes then begin to be moved around, and this seems to be being done by molecules called motor proteins.
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And while we don't know too much about how these motors work, we do know, for instance,
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that there are two of them on each side of the centromere.
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These are called centromere -associated protein E.
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So these motor proteins attached to the microtubule ropes basically serve to spool up the tubule slack.
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At the same time, another protein called dynion is pulling up the slack from other ends of the ropes near the cell membranes.
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After being pulled in this direction and that, the chromosomes line up right down the middle of the cell.
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And that brings us to the latest installment of Biolography.
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So how do chromosomes line up like that?
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We know that there are motor proteins involved, but like, how?
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What are they doing?
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Well, remember when I said earlier that there were a lot of things that we don't totally understand about mitosis?
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It's sort of weird that we don't, because we can literally watch mitosis happening under microscopes.
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But chromosome alignment is a good example of a small detail that has only very recently been figured out.
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And it was a revelation like 130 years in the making.
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Mitosis was first observed by a German biologist by the name of Walter Fleming, who in 1878 was studying the tissue of salamander,
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gills, and fins when he saw cells' nuclei split in two and migrate away from each other to form two new cells.
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He called this process mitosis, after the Greek word for thread because of the messy jumble of chromatin,
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a term he also coined that he saw in the nuclei.
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But Fleming didn't pick up on the implications of this discovery for genetics, which was still a young discipline.
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And over the next century, generations of scientists started piecing together the mitosis puzzle by determining the role of microtubules, say, or identifying motor proteins.
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Now the most recent contribution to this research was made by a postdoctoral student named Tomomi Kiyomitsu at MIT.
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He watched the same process that Fleming watched
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and figured out how at least one of the motor proteins helped snap the chromosomes into line.
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He was studying a motor protein called dynion, which sits on the inside of the membrane.
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Think of the microtubules as tug -of -war ropes, with the chromosomes as the flag in the middle.
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What Kiyomitsu discovered was that the Dainian plays tug -of -war with itself.
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Dainian grabs onto one end of the microtubules and pulls the tubules and chromosomes toward one end of the cell.
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When the ends of the microtubules come too close to the cell membrane,
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they release a chemical signal that punts the Dainian to the other side of the cell.
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There, it grabs onto the other end of the microtubules and starts pulling until until smack, it gets punted back again.
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All of this ensures that the chromosomes will line up exactly in the middle, so that they will be split evenly.
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That discovery was published in February of 2012, a couple of weeks before I sat down in this chair,
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and 134 years after mitosis was first observed.
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If you want to join the ranks of scientists who are answering the many questions left about mitosis
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and lots of other things about our lives, maybe someday I'll do a biolography about you.
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Now so far we've gone through the interphase, where the centrosomes in DNA replicate themselves and get ready for the split.
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The prophase, where the chromosomes form and the centrosomes start to spread apart.
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And the metaphase, where the chromosomes align in the middle of the cell.
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And now it's time to separate the chromosomes from their copies.
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This time, motor proteins start pulling so hard on the ropes
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that the X -shaped chromosomes split back into their individual single chromosomes.
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Once they're detached from each other, they're dragged toward either end of the cell.
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Since the prefix ana means back, that may help you remember the name of this phase called anaphase.
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After this, it's just a matter of using all that genetic material to rebuild,
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so that the copied genetic material has all of the accoutrements of home.
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In the last phase, telophase, each of the new cell structures are reconstructed.
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First, the nuclear membrane reforms, the nucleoli form within them, and the chromosomes relax back into chromatin.
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Then a little crease forms between the two new cells, which marks the beginning of the final split.
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That division between the two new cells is called cleavage, and all that's left is to make a clean break.
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This is done by cytokinesis, literally cell movement, by which the two new nuclei move apart from each other, and the cells separate.
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We now have two new cells, each with a full set of 46 chromosomes.
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These clones are called the daughter cells of the original cell,
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and like identical twins, they are genetic copies of each other and also of their parents.
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But of course, that's obviously not the case for you, even if you are an identical twin.
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Shout out identical twins!
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See me in the comments.
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While you kind of are a clone of your sibling, you are not a clone of your parents.
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Instead, half of your DNA in each of your cells is from your mom and half is from your dad.
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To understand why that is, we have to understand how eggs and sperm are formed, and that is meiosis.
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And that's what we're going to be talking about next week on Crash Course.
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Until then, you can just watch this video over and over again,
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or you can just watch the bits that you want to rewatch using our table of contents,
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which is also available in the description for people who are using iPhones and can't click annotations.
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If you have any questions, you can reach us on Facebook or on Twitter, or of course, in the comments below.
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Vocabulário e dicas de fala para esta lição
Esta aula de conversação usa o vídeo “Mitosis: Splitting Up is Complicated - Crash Course Biology”. As palavras que mais se repetem: cell, chromosome, mitosis, Dna, protein. Este vídeo tem 146 frases e 2110 palavras para praticar shadowing. A fala dura 10:38. O falante fala rápido, cerca de 199 palavras por minuto, então espere sons ligados e reduzidos. 83% das palavras estão entre as 3.000 mais comuns do inglês; vale a pena estudar o restante antes de começar.
Vocabulário principal deste vídeo
15 palavras do vídeo que vale a pena aprender, com pronúncia e significado:
| Palavra | Pronúncia | Significado |
|---|---|---|
| nucleus substantivo | /ˈnuː.kli.əs/ | núcleo |
| clone substantivo | /kloʊn/ | clone |
| rope substantivo | /ɹoʊp/ | corda |
| identical adjetivo | /ɪˈdɛntɪkl̩/ | idêntico |
| duplicate verbo | /ˈd(j)uː.plɪˌkeɪt/ | duplicar |
| genetic adjetivo | /d͡ʒəˈnɛt.ɪk/ | genético |
| twin substantivo | /twɪn/ | gémeo, gémea |
| messy adjetivo | /ˈmɛsi/ | desorganizado, bagunçado |
| membrane substantivo | /ˈmɛm.bɹeɪn/ | membrana |
| attach verbo | /əˈtæt͡ʃ/ | anexar |
| strand substantivo | /ˈstɹænd/ | cordel |
| replicate verbo | /ˈɹɛplɪkeɪt/ | replicar |
| discovery substantivo | /dɪˈskʌv.ɹi/ | descoberta |
| dust substantivo | /dʌst/ | pó, poeira |
| scientist substantivo | /ˈsaɪəntəst/ | cientista |
Phrasal verbs que você vai ouvir
| Palavra | Pronúncia | Significado |
|---|---|---|
| figure out verbo | descobrir, deduzir | |
| check out verbo | verificar, sacar só | |
| clean up verbo | dar uma limpeza, limpar | |
| pull up verbo | /ˌpʊl ˈʌp/ | puxar para cima |
| wrap up verbo | embrulhar, empacotar |
Frases que vale a pena repetir
Frases curtas e completas do vídeo que você pode usar na conversa do dia a dia:
- We're gonna talk about those in the next episode.
- Tumor growing in your spine?
- Alright, let's get our clone on.
- We know that there are motor proteins involved, but like, how?
Gramática neste vídeo
As estruturas que o falante mais usa, com as palavras exatas do vídeo:
| Estrutura | No vídeo |
|---|---|
| Voz passiva be + particípio passado — o foco está no que acontece, não em quem faz | is called · are made · is organized |
| Present perfect have/has + particípio passado — uma ação passada que ainda importa agora | we've mentioned · have been made · we've gone |
| Orações relativas who / which + oração — informação extra sobre uma pessoa ou coisa | interphase, which means · genetics, which was · people who are |
Pronúncia para ficar de olho
O falante usa 35 contrações e formas reduzidas, como they're, don't, we're. Diga-as na forma curta, do jeito que você ouve.
- Os sons de “th”: thick /θɪk/, thread /ˈθɹɛd/
- Os sons de “sh” e “zh”: instruction /ɪnˈstɹʌkʃən/, contribution /ˌkɑntɹɪˈbjuʃən/, tissue /ˈtɪʃ.(j)u/, brush /bɹʌʃ/, shout /ʃaʊt/
- Palavras longas — acerte a sílaba tônica: organism /ˈɔɹ.ɡəˌnɪz.əm/, contribution /ˌkɑntɹɪˈbjuʃən/, mechanism /ˈmɛk.ə.nɪ.zəm/, surprisingly /səˈpɹaɪzɪŋli/, revelation /ˌɹɛv.əˈleɪ.ʃən/
Sons difíceis para falantes de português:
- Consoante final — sem acrescentar um “i” depois: rope /ɹoʊp/, duplicate /ˈd(j)uː.plɪˌkeɪt/, genetic /d͡ʒəˈnɛt.ɪk/, strand /ˈstɹænd/, replicate /ˈɹɛplɪkeɪt/
- /l/ final — a língua toca o céu da boca, não vira “u”: coil /kɔɪl/, trail /tɹeɪl/, recall /ɹɪˈkɔl/, heal /ˈhiːl/, puzzle /ˈpʌzəl/
- /h/ — um sopro suave, diferente do “r”: heal /ˈhiːl/, haploid /ˈhæplɔɪd/
Como praticar com este vídeo
- Ouça o vídeo inteiro uma vez sem falar e anote as palavras que você não conhece.
- Comece na velocidade 0,75×, faça shadowing frase por frase e volte à velocidade normal quando ficar fácil.
- Grave a sua voz e compare com o original, prestando atenção a palavras como nucleus, clone, rope.
O que é a Técnica de Shadowing?
Shadowing é uma técnica de aprendizado de idiomas com base científica, originalmente desenvolvida para o treinamento de intérpretes profissionais. O método é simples, mas poderoso: você ouve áudio em inglês nativo e repete imediatamente em voz alta — como uma sombra seguindo o falante com 1-2 segundos de atraso. Pesquisas mostram melhora significativa na precisão da pronúncia, entonação, ritmo, sons conectados, compreensão auditiva e fluência na fala.