シャドーイング練習: Mitosis: Splitting Up is Complicated - Crash Course Biology #12 - 動画で英語スピーキングを学ぶ

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Now check this out.

Ha, cool huh?

I bet you wish you could do this.

Have a clone, clean up around the apartment for you, go to class, maybe take your mom out to dinner on her birthday.

Well, you can't do that, and actually there are some really good reasons why you can't do that.

We're gonna talk about those in the next episode.

But you know what can clone themselves?

Your cells.

Like almost every single one of them, and in fact, they're doing it right now.

For any creature bigger than a single -celled organism, all of life stems from cells' ability to reproduce themselves

because that's what allows organisms to develop and grow and heal and keep from dying for as long as possible.

This particular kind of cell division is called mitosis and it's responsible for a whole lot of your body's key functions.

If you get it cut, your body needs to make new cells.

Mitosis.

Have too much to drink?

Damage your liver?

You gotta replace those cells.

Mitosis.

Tumor growing in your spine?

Unfortunately, again, mitosis.

While you go from a seven pound baby to a 70 pound child, it's not your cells that are increasing in mass,

you're just getting more of them over and over and over again.

That's mitosis.

This process is so central to your life that it will take place in your body, over your lifetime, about 10 quadrillion times.

That's 10 ,000 billion times.

Like all split ups, it's not easy.

It's gonna maybe be a little bit messy.

There's a lot of drama and it can take a surprisingly long amount of time

But trust me after we're done with it.

We'll all be better off

So you are made of trillions of cells just like giraffes

and redwood trees and remember that inside each cell there's a nucleus

that stores your DNA which contains all of the instructions on how to build you.

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.

One in each pair is from your mom, and the other one is from your dad.

Cells with all 46 chromosomes are called diploid cells because they have two sets each, and that's what we're focusing on today.

You also have haploid cells that have half as many chromosomes as 23.

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.

But for now, the main thing to remember about mitosis is

that it allows one cell with 46 chromosomes to split into two cells that are genetically identical,

each with 46 chromosomes, all in order to keep the party of life going.

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,

so you don't need to duplicate the whole cell.

All you need to do is duplicate the DNA, get it wrapped up, and then if you have two separate pockets of DNA,

that's all you need to have two new cells.

Mitosis takes place in a series of discrete stages called prophase, metaphase, anaphase, and telophase.

And you could just say that over and over again and let it sink into your head.

And part of what's, you know, really amazing about this whole process is that while we know what these stages are,

we don't always know the underlying mechanisms that make all of them happen.

And this is part of science.

Science isn't like all the stuff we know, it's how we're trying to figure all this stuff out.

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.

And this is one of them.

Alright, let's get our clone on.

So most of their lives, cells hang out in this limbo period called interphase, which means they're in between episodes of mitosis.

Mostly growing and working and doing all the stuff that makes them useful to us.

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.

That mess of DNA is called chromatin.

But as the mitosis process begins to gear up, lots of things start happening in the cell to get ready for the big division.

One of the more important things that happens is

that this little set of protein cylinders next to the nucleus called the centrosome duplicates itself.

We're gonna have to move a lot of stuff around in the nucleus, and that's gonna be regulated by these centrosomes.

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.

To brush up on how DNA replicates itself like this, check out this episode and then come on back.

Now the cell enters the first phase, or the prophase, when that mess of chromatin condenses

and coils up on itself to produce thick strands of DNA wrapped around proteins.

Those, my friends, are your chromosomes.

Instead of dust bunnies, the DNA is starting to look a little bit more like dreadlocks.

And the duplicates that have been made don't just float around freely.

They stay attached to the original, and together they look like little X's.

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.

Where they meet in the middle is called the centromere.

Just so you know, these X's are also called chromosomes, sometimes double chromosomes or double -stranded chromosomes,

and when the chromatids separate.. they're considered individual chromosomes too.

Now while the chromosomes are forming, the nuclear envelope gets out of the way by like, completely disintegrating.

And the centrosomes then peel away from the nucleus, start heading to the opposite ends of the cell.

As they go, they leave behind a wide trail of protein ropes called microtubules, running from one centrosome to the other.

You might recall from our anatomy of the animal cell, that microtubules help provide a kind of structure to the cell.

This is exactly what they're doing here.

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.

During the metaphase, the chromosomes attach to those ropey microtubules right in the middle at their centromeres.

The chromosomes then begin to be moved around, and this seems to be being done by molecules called motor proteins.

And while we don't know too much about how these motors work, we do know, for instance,

that there are two of them on each side of the centromere.

These are called centromere -associated protein E.

So these motor proteins attached to the microtubule ropes basically serve to spool up the tubule slack.

At the same time, another protein called dynion is pulling up the slack from other ends of the ropes near the cell membranes.

After being pulled in this direction and that, the chromosomes line up right down the middle of the cell.

And that brings us to the latest installment of Biolography.

So how do chromosomes line up like that?

We know that there are motor proteins involved, but like, how?

What are they doing?

Well, remember when I said earlier that there were a lot of things that we don't totally understand about mitosis?

It's sort of weird that we don't, because we can literally watch mitosis happening under microscopes.

But chromosome alignment is a good example of a small detail that has only very recently been figured out.

And it was a revelation like 130 years in the making.

Mitosis was first observed by a German biologist by the name of Walter Fleming, who in 1878 was studying the tissue of salamander,

gills, and fins when he saw cells' nuclei split in two and migrate away from each other to form two new cells.

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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このレッスンの語彙とスピーキングのポイント

このスピーキングレッスンは、動画「Mitosis: Splitting Up is Complicated - Crash Course Biology」を教材にしています。繰り返し出てくる語は次のとおりです：cell, chromosome, mitosis, Dna, protein。この動画には、シャドーイング用の文が146文、単語が2110語あります。音声の長さは10:38です。話す速さは速く、1分あたり約199語です。音のつながりや弱く発音される音が多くなります。単語の83%は英語の頻出3,000語に含まれます。残りは練習の前に確認しておきましょう。

この動画の重要語彙

動画に出てくる覚えておきたい単語15語を、発音と意味つきで紹介します。

単語	発音	意味
nucleus 名詞	/ˈnuː.kli.əs/	核, 核心
clone 名詞	/kloʊn/	クローン
rope 名詞	/ɹoʊp/	ロープ, 綱
identical 形容詞	/ɪˈdɛntɪkl̩/	同一の, そっくりの
duplicate 動詞	/ˈd(j)uː.plɪˌkeɪt/	複写する, 複製する
genetic 形容詞	/d͡ʒəˈnɛt.ɪk/	遺伝的
twin 名詞	/twɪn/	双子
messy 形容詞	/ˈmɛsi/	乱雑な, きたない
membrane 名詞	/ˈmɛm.bɹeɪn/	膜
attach 動詞	/əˈtæt͡ʃ/	付ける, 添付する
discovery 名詞	/dɪˈskʌv.ɹi/	発見
dust 名詞	/dʌst/	埃, ほこり
scientist 名詞	/ˈsaɪəntəst/	科学者
wrap 動詞	/ɹæp/	包む, 包装する
instruction 名詞	/ɪnˈstɹʌkʃən/	指示

動画に出てくる句動詞

単語	発音	意味
check out 動詞		試験する, 検査する
clean up 動詞		掃除する
leave behind 動詞		置き忘れる
pull up 動詞	/ˌpʊl ˈʌp/	引き上げる

繰り返し練習したい文

動画に出てくる短く完結した文です。日常会話でそのまま使えます。

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?

この動画の文法

話し手がよく使っている文型を、動画の実際の表現とともに紹介します。

文型	動画での表現
受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる	is called · are made · is organized
現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している	we've mentioned · have been made · we've gone
関係詞節 who / which + 節 — 人や物について情報を加える	interphase, which means · genetics, which was · people who are

注意したい発音

話し手はthey're, don't, we'reなど、短縮形や弱形を35回使っています。聞こえたとおりの短い形で発音しましょう。

「th」の音: thick /θɪk/, thread /ˈθɹɛd/
「sh」と「zh」の音: instruction /ɪnˈstɹʌkʃən/, contribution /ˌkɑntɹɪˈbjuʃən/, tissue /ˈtɪʃ.(j)u/, brush /bɹʌʃ/, shout /ʃaʊt/
長い単語（アクセントの位置に注意）: organism /ˈɔɹ.ɡəˌnɪz.əm/, contribution /ˌkɑntɹɪˈbjuʃən/, mechanism /ˈmɛk.ə.nɪ.zəm/, surprisingly /səˈpɹaɪzɪŋli/, revelation /ˌɹɛv.əˈleɪ.ʃən/

日本語話者が苦手な音：

/r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: replicate /ˈɹɛplɪkeɪt/, trail /tɹeɪl/, recall /ɹɪˈkɔl/, relax /ɹɪˈlæks/, surprisingly /səˈpɹaɪzɪŋli/
/v/ — /b/ にならないように、上の歯を下唇に当てる: discovery /dɪˈskʌv.ɹi/, observe /əbˈzɜːv/, revelation /ˌɹɛv.əˈleɪ.ʃən/, envelope /ˈɛnvə(ˌ)loʊp/, evenly /ˈiːvənli/
/f/ — 「フ」ではなく、上の歯と下唇で出す: lifetime /ˈlaɪf.taɪm/, freely /ˈfɹili/, float /fləʊt/, fin /fɪn/, anaphase /ˈænəˌfeɪz/

この動画での練習方法

まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
自分の声を録音して元の音声と比べます。nucleus, clone, ropeなどの単語に特に注意しましょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。

シャドーイングのやり方: ステップ別の完全ガイドを読む →

シャドーイング練習: Mitosis: Splitting Up is Complicated - Crash Course Biology #12 - 動画で英語スピーキングを学ぶ

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