Life is made of cells. It's the basic unit of structure and function. And also all cells

生命是由細胞組成的。它'是結構和功能的基本組織、部門。也是所有細胞

we have must come from preexisting cells. And so how does that work? It's through a

我們所擁有的一定是來自於現有的細胞。那麼這又是怎麼做到的呢？它是通過一個

process called cell division. This is going to occur in all cells, both prokaryotic like

稱為細胞分裂的過程。這在所有細胞中都會發生，無論是原核細胞還是像

bacteria and eukaryotic like you. And through cell division one cell can become two. Which

細菌和你這樣的真核生物。而通過細胞分裂，一個細胞可以變成兩個。哪種

can quickly become four and then eight and then sixteen. And so we get exponential growth

可以很快變成4個，然後是8個，然後是16個。所以我們得到了指數級的增長

in cells. And to give you an idea how quickly this goes, you started life as one fertilized

細胞中。為了讓你知道這一切有多快，你的生命是從一個受精開始的。

egg. Or one zygote. But those were quickly dividing over time. And it eventually created

卵子。或者是一個胚胎。但隨著時間的推移，這些都在迅速分裂。最終形成了

an adult that's going to have around 10 trillion cells inside your body. And they all came

一個成年人的體內會有大約10萬億個細胞。而他們都來了

from that original cell. Now to even increase that number quite a bit, just look in your

從最初的細胞。現在，為了增加這個數字，只要看看你的

gut and we're going to find that the bacteria living in your digestive tract are going to

腸道和我們'會發現，生活在你的消化道的細菌是要

outnumber the cells in your whole body ten to one. There are going to be 100 trillion

比你全身的細胞數量多十倍。將會有100萬億

bacteria just living in your gut. And they're going to be outnumbered about 10 to one by

細菌只是生活在你的腸道。而他們將是寡不敵眾 大約10到一個由

viruses living in your gut. So we're going to have quadrillion viruses living in your

病毒生活在你的腸道。所以，我們將有四萬億病毒 生活在你的腸道。

gut. Now viruses aren't technically cells, but everything else I've described here is

腸道。現在，病毒不是技術上的細胞，但其他一切我'這裡描述的是。

going to be reproducing or it's going to be created through a process called cell division.

將會進行繁殖，或者它將會通過一個叫做細胞分裂的過程被創造出來。

And there are really three types of cell division. In prokaryotic cells, or in bacteria, they're

而細胞分裂其實有三種類型。在原核細胞或細菌中，它們是：

simply going to divide through a process called binary fission. That's where one cell, one

只是要通過一個叫做二元裂變的過程來分裂。這就是一個細胞，一個

bacteria cell, is going to make two cells that are exact copies of the original cell.

細菌細胞，是要製造出兩個完全複製原細胞的細胞。

In eukaryotic cells we have something similar to this. We're going to have cell division

在真核細胞中，我們有類似的東西。我們要進行細胞分裂。

or we sometimes just refer to it as mitosis. Technically mitosis is going to be division

或者我們有時就把它稱為有絲分裂。從技術上講，有絲分裂就是要分裂

of the nuclei. And then we're going to have cytokinesis which is division of the rest

細胞核的。然後我們會有細胞分裂，這是其餘的分裂。

of the cell. But we generally just say mitosis is when one eukaryotic cell makes two cells

的細胞。但我們一般只是說有絲分裂是一個真核細胞製造兩個細胞的時候

that are exact copies of that cell. It's a lot like binary fission. And then the third

是該細胞的精確拷貝。這很像二元裂變。然後第三種

type of cell division is going to be meiosis. Meiosis is going to be when we create sex

細胞分裂的類型將是減數分裂。減數分裂將是我們創造性的時候。

cells. Or when we create gametes. Mitosis and binary fission insure that we have exact

細胞。或者當我們創造配子時。有絲分裂和二元裂變保證了我們有確切的。

duplicates of that original cell. Meiosis is totally different. Meiosis is going to

該原始細胞的副本。減數分裂則完全不同。減數分裂是要

make cells that are different. They're going to have half the genetic information and they're

使細胞是不同的。他們將有一半的遺傳信息和他們的。

going to give us variability. And so in us sex is important because it gives us variability

會給我們帶來變異性。所以對我們來說，性是很重要的，因為它給我們帶來了變異性

in the next generation. In bacteria mutation and there's some other ways that they can

在下一代。在細菌突變和有一些其他的方式，他們可以。

share information is more important. So let's start by talking about bacteria. They reproduce

分享資訊更重要。所以，讓我們'從細菌開始說起。它們的繁殖

through a process called binary fission. In this we're going to have this adult cell,

通過一個叫做二元裂變的過程。在這個我們'要有這個成體細胞。

so we're going to have this parent cell. It's going to be made up of, you can see here,

所以我們將有這個父細胞。它將會由，你可以看到這裡。

ribosomes. It's going to have a plasmid here which is a little bit of extra DNA. But it's

核糖體。它將有一個質粒在這裡 這是一個有點額外的DNA。但它

genome or all of its DNA is going to be wrapped up into one loop. And so what do we want to

基因組或其所有的DNA將被包裹成一個循環。所以我們要做的是

do in binary fission? We want to take one cell and we want to make two cells that are

做二元裂變？我們想用一個細胞來製造兩個細胞，這兩個細胞是...

identical to that. And so the process is pretty simple. What the bacteria cell starts doing

與此相同。所以這個過程非常簡單。細菌細胞開始做什麼

is duplicating all of its DNA. So the first thing it will do is DNA polymerase goes around

正在複製所有的DNA。所以它要做的第一件事就是DNA聚合酶繞著它跑

the whole loop and it's going to make an exact copy of all the DNA in the bacteria. One thing

整個循環，它'的要做一個精確的副本 所有的DNA在細菌。有一件事

not shown in here is that we're also going to duplicate our plasmids. And we're also

在這裡沒有顯示的是，我們'也要複製我們的質粒。而且我們'也

going to have, you know, ribosomes increasing as we increase the number of DNA as well.

將有，你知道，核糖體增加 當我們增加DNA的數量，以及。

What happens next is it's going to be pulled to the side of that cell. And really what's

接下來發生的事情就是它'會被拉到那個小區的旁邊。而真正的...

going to happen is the DNA will actually attach to the cell wall. And then eventually that

將會發生的是DNA將實際附著在細胞壁上。然後最終

cell wall is going to split in half and we're going to have two bacteria cells. How are

細胞壁將分裂成兩半，我們'將有兩個細菌細胞。如何是

they different? They're not really different. They're exactly the same. The DNA in this

他們不同？他們並沒有真正的不同。他們是完全一樣的。這裡面的DNA

cell and the DNA in this cell is going to be exactly the same. And when we divide in

細胞和這個細胞中的DNA是完全一樣的。而當我們分裂的時候

half, we're going to divide in half those ribosomes and the plasmids as well. And so

一半，我們'要抽成一半那些核糖體和質粒也是如此。我們要把這些核糖體和質粒也抽成兩半

again, bacteria don't do mitosis. They don't have sex. They simply reproduce through binary

再次，細菌不'不做有絲分裂。他們不'沒有性別。它們只是通過二元繁殖

fission. And this happens incredibly quickly. So in a typical e. coli they can copy themselves,

裂變。而且這種情況發生得非常快所以在一個典型的大腸桿菌中，它們可以複製自己。

make two copies of one cell, in 20 minutes. Which is just crazy how fast that occurs.

在20分鐘內將一個細胞複製兩份。這就是瘋狂的發生速度。

But again we don't go through binary fission because we're eukaryotic cells. And before

但我們又不經過二元裂變，因為我們'是真核細胞。而之前

we talk about mitosis and meiosis, we should make sure you know the difference between

我們談論有絲分裂和減數分裂，我們應該確保你知道兩者之間的區別。

what a gamete is and then a somatic cell. And so eukaryotic cells are going to be everything

什麼是配子，然後是體細胞。所以真核細胞將成為所有的東西

from the chimpanzee to the bees to the flowers to the mushroom to the yeast, they all have

從黑猩猩到蜜蜂到花兒到蘑菇到酵母，它們都有...

a nuclei. And so there are two types of cells that we find inside eukaryotic organisms.

一個細胞核。所以我們在真核生物體內發現了兩種類型的細胞。

First are going to be the somatic cells. Somatic cells are going to be the body cells in your

首先是會是體細胞。體細胞將是你的身體細胞。

body. And then we're going to have the gametes which are going to be the sex cells. So in

身體。然後我們'將有配子 這將是性細胞。所以在

humans the only cells inside our body that are going to be gametes are going to be sperm

人類體內唯一能成為配子的細胞就是精子。

in males and then the eggs or the ovum that are found inside females. How are they different?

在雄性體內的卵子或卵子，然後在雌性體內發現。它們有什麼不同？

Remember somatic cells are the body cells that are going to be diploid in humans. They're

記住體細胞是人類要二倍體的體細胞。他們'是

going to have two copies of every gene. And therefore two copies of every chromosome.

將有兩個副本 每個基因。是以每條染色體都有兩個拷貝。

Gametes are only going to have one. So sperm and egg each provide you with half the DNA

配子是隻會有一個的。所以精子和卵子各為你提供一半的DNA。

that you get. So how do we duplicate a typical cell? Well first we should say when do we

你得到的。那麼我們如何複製一個典型的細胞呢？好吧，首先我們應該說，當我們

do that? Well remember when you go from a zygote to an adult, we're doubling the cells

做到這一點？ - 好吧，記得當你從胚胎到成人，記得當你從一個胚胎變成一個成年人的時候 我們的細胞就會翻倍

over and over and over again. And then we're constantly replacing the cells in our body.

一遍又一遍。然後我們'不斷地更換體內的細胞。

So as cells become worn out or damaged or removed we have to replace those with other

所以，當細胞磨損、損壞或被移除時，我們必須用其他的細胞來替代這些細胞。

cells. And we do that through mitosis. Again what is mitosis? It's technically the division

細胞。我們通過有絲分裂來實現。同樣什麼是有絲分裂？它的技術上的分裂

of the nuclei, but then we're going to have division of the rest of the cell which is

細胞核，但隨後我們'將有分裂 細胞的其餘部分，這是。

called cytokinesis. So what do we start with? And we're going to make this real simple,

稱為細胞運動學。那麼我們從什麼開始呢？而我們'將使這個真正的簡單。

this is a simple cell. It's a diploid cell. It's 2n=2. That means they have two chromosomes.

這是一個簡單的細胞。這是一個簡單的細胞。 這是一個二倍體細胞。它是2n=2。這意味著他們有兩條染色體。

These two chromosomes are going to be homologous. That means that they're the same length. The

這兩條染色體將是同源的。這意味著他們'是相同的長度。這

reason why they're different colors is you get on from one parent and one from another.

為什麼他們'不同的顏色的原因是你從一個父母和一個從另一個得到上。

And so in mitosis, let's look first before we talk about the specifics of what we're

所以在有絲分裂中，我們先來看看，然後再來談談我們的具體內容。

going to get out of mitosis. We're going to start with one cell looks like this. And we're

要走出有絲分裂。我們要開始與一個細胞看起來像這樣。我們要從一個像這樣的細胞開始

going to end up with two cells that look exactly like that first cell. So in mitosis we want

最終會有兩個和第一個細胞一模一樣的細胞。所以在有絲分裂過程中，我們要

to duplicate the cell. And so let's watch that. What's the first thing that happens

來複制細胞。所以，讓我們'觀看。首先發生的事情是什麼？

is we have to duplicate all of the DNA. And this occurs during interphase. What's going

是我們必須複製所有的DNA。而這發生在間期。什麼？

to happen is this chromosome right here is going to copy all of its DNA. And now we're

這條染色體將複製所有的DNA。現在我們

going to have what are called sister chromatids. And so we have a chromosome on this side.

會有所謂的姐妹染色體。所以，我們有一個染色體 在這一側。

A chromosome on this side. And they're exactly the same. So they're an exact duplicate of

這邊的一條染色體。而且它們是完全一樣的。所以他們是一個完全重複的。

that original chromosome. And you can see that we're going to have that on the other

原始染色體。你可以看到，我們'將有 在另一個。

homologous chromosome as well. What happens next? They're going to meet in the middle.

同源染色體也是如此。接下來會發生什麼？他們'會在中間相遇。

They're going to line up. These lines represent a spindle which is going to attach to either

他們'要排成一條線。這些線條代表了一個主軸，它將連接到任何一個地方。

side. Each of those sister chromatids and then they're going to be pulled apart. They're

一邊。每一個姐妹染色體，然後他們'將被拉開。姐妹染色體

going to be pulled apart. And eventually, so this would be the mitosis when we divide

會被拉開。最終，所以這將是有絲分裂，當我們分裂的時候，

the nuclei. And then the whole cell is going to split in half. We're going to divide that

細胞核。然後整個細胞將被一分為二。我們要把它抽成兩半

cytoplasm and that's called cytokinesis. And so what do we end up with? We end up with

細胞質和'叫細胞分裂。所以，我們最終與什麼？我們的結局是

two cells that are both diploid. Our original cell was diploid as well. So let's take a

兩個細胞，都是二倍體。我們原來的細胞也是二倍體。所以，讓我們以

look at what this really looks like. We're looking right here at cells that are undergoing

看看這到底是什麼樣子。我們現在看到的是正在進行中的細胞。

mitosis. And so they're growing on a growth medium. And if we just play the video, this

有絲分裂。所以他們'生長在一個生長介質上。如果我們只是播放視頻，這

is time lapsed. And so it's speeding it up quite a bit. But what will happen if we look

是時間的推移。所以它'的速度相當快。但是，如果我們看看會發生什麼

at like this cell right down here, is that you can see it kind of come together in the

在像這樣的細胞就在這裡， 是，你可以看到它的那種走到一起的。

nuclei's dividing up the genetic information. And then the rest of the cell is going to

細胞核正在分割遺傳信息。細胞的其餘部分將是

divide. What do we end up with when we're done with that? We have two identical cells.

分裂。當我們做完這一切後，我們最終會得到什麼？我們有兩個相同的細胞。

And those are going to grow. And then they're eventually going to divide the nuclei and

而這些都會成長。然後他們最終會分裂出細胞核和

they're going to grow. And they're going to grow. And they're going to grow. And cells,

他們'要成長。而他們'要成長。他們會成長。 而他們'要成長。和細胞。

unless they're cancer cells, are going to keep growing on here until they fill up this

除非他們'是癌細胞，要保持增長在這裡，直到他們填補了這個

whole medium. But we need to talk about meiosis, which is the third type of cell division.

整個介質。但我們需要談談減數分裂，這是細胞分裂的第三種類型。

What happens in meiosis. Meiosis is when you take one cell and we're going to make four

減數分裂中發生了什麼。減數分裂是當你把一個細胞和我們'要做四個。

cells out of it. Now let's look how this is a little different than in mitosis. In mitosis

細胞出來的。現在讓我們來看看這與有絲分裂中的情況有什麼不同。在有絲分裂中

remember we took one cell and we made two cells. In meiosis we're actually going to

記得我們把一個細胞和我們做了兩個細胞。在減數分裂中，我們實際上要

have another division. But there's something even different that we didn't see in mitosis.

有另一個分部。但有'的東西甚至不同，我們在有絲分裂中沒有看到。

Remember in mitosis we want to make sure that each of the cells that we make are identical

記住，在有絲分裂中，我們要確保我們製造的每一個細胞都是相同的。

to that original cell. You can see here that the four cells that we create at the end are

到那個原始單元格。在這裡你可以看到，我們在最後創建的四個單元格是

going to be totally different than that original cell. And they're going to have half the genetic

將是完全不同的 比原來的細胞。他們將有一半的基因。

information. Remember I said the sperm and the egg have half the information that's found

資訊。記得我說過精子和卵子有一半的資訊，'的發現。

in the original cell. And so what's going happen? Well let's watch how this begins.

在原來的細胞中。那麼會發生什麼呢？好吧，讓我們來看看這是如何開始的。

The first thing that happens is you're going to duplicate each of these chromosomes. And

第一件事就是你'要複製這些染色體的每一條。而

so we're going to make copies of the chromosomes. But then something odd happens. What happens

所以我們'要對染色體進行復制。但後來發生了一些奇怪的事情。發生了什麼？

that's odd, we're going to take a little bit, in the case we're going to take a little bit

這是奇怪的，我們將採取一點點，在這種情況下，我們將採取一點點。

of this white chromosome here. And it's going to cross over with this red chromosome right.

這個白色染色體的這裡。和它'的要交叉 與這個紅色的染色體權利。

So we're actually swapping chromosomes. And so that process is called crossing over but

所以我們實際上是在交換染色體。所以這個過程被稱為越界，但

what you're really doing is your crossing over or your making a new chromosome. It's

你真正做的是你的交叉或你做一個新的染色體。它是

a combination of the chromosome you got from your mom and your dad. It's a chromosome that's

你從你的媽媽和你的爸爸得到的染色體的組合。它是一個染色體，它的

never been built before. So those will eventually line up in the middle. And then they're going

從來沒有建過。所以，這些最終會排在中間。然後他們'要

to divide. And then they're going to divide again. And so they'll divide in half. So this

分裂。然後他們'要再次分裂。所以他們'會一分為二。所以這

is meiosis one and then they'll divide in half again. And that is called meiosis two.

是減數分裂一，然後他們'會再次分裂成兩半。這就是所謂的減數第二次分裂。

So what do we create when we're done. We're going to create daughter cells. But each of

那麼，當我們'完成後，我們要創建什麼。我們'要創造子細胞。但每個

those daughter cells are going to be different. Each of these would create a new sperm or

這些子細胞將是不同的。每一個子細胞都會創造出一個新的精子，或者說是一個新的子細胞。

a new egg. Now it's going to be much more complicated in us, in humans, remember, we're

一個新的雞蛋。現在，這將是更復雜的我們，在人類，記住，我們'。

not going to start with 2n=4. With 4 total chromosomes here. We're going to start with

不打算從2n=4開始。與4總染色體在這裡。我們要從

2n=46. And so we're going to start with 46 chromosomes. So it's going to be really really

2n=46.所以我們要從46條染色體開始。所以，這將是真的真的真的

different when we get to the end. And so we can create literally billions and billions

不同的時候，我們得到的最後。所以我們可以創造出數以億計的東西

of different types of cells through meiosis. And so that's going to give us variation.

的不同類型的細胞通過減數分裂。所以，這'將給我們的變化。

So to summarize. What do we have? We have three types of cell division. We've got binary

所以要總結一下。我們有什麼？我們有三種類型的細胞分裂。我們有二元分裂

fission. That's going to be found just in bacteria where you take one bacteria, first

裂變。這'要在細菌中就能發現，你把一個細菌，先是。

copy the DNA and then the rest of the cell is going to divide through cytokinesis. Each

複製DNA，然後細胞的其他部分通過細胞分裂。每個

of these daughter cells is going to be identical to that first cell. If you're looking at eukaryotic

這些子細胞的要和第一個細胞相同。如果你看的是真核細胞

cells, we've got mitosis. What happens in mitosis? We start with a diploid cell. So

細胞，我們已經得到了有絲分裂。有絲分裂會發生什麼？我們開始與二倍體細胞。所以...

here are the reds and the greens are each going to come from different parents. So we

這裡的紅色和綠色都是來自不同的父母。所以我們

have four chromosomes. They're going to duplicate first during S phase of interphase. They'll

有四條染色體。它們會在間期的S階段首先複製。他們將

line up in the middle. And they'll be pulled to the side. Now if we look here, these two

排在中間。而他們'會被拉到一邊。現在如果我們看這裡，這兩個

cells that are produced in mitosis are identical to that original cell. And that's what mitosis

在有絲分裂中產生的細胞與該原始細胞是相同的。而這正是有絲分裂

does. It makes exact copies. If we start with meiosis, meiosis is going to start with an

是的它能做出精確的拷貝。如果我們從減數分裂開始，減數分裂將從一個新的開始。

original cell that looks very similar. But instead of lining up like this where we separate

原始單元格，看起來非常相似。但我們不是像這樣排成一排，在這裡，我們分開了

the sister chromatids, they're going to line up with the homologous chromosomes wrapping

姐妹染色體，它們將與包裹著同源染色體的同源染色體排在一起

around each other and swapping bits of that chromosome. They'll divide in half. And then

互相圍繞，交換該染色體的位。它們會一分為二。然後

they're going to divide in half again. And what we're going to create is gametes. Those

他們將再次分裂成兩半。而我們要創造的是配子。那些...

are going to be sperm and egg that have half the genetic information in a new combination

將是精子和卵子，有一半的遺傳信息的新組合。

of that genetic information. So again, this will be fertilized by a different sperm and

的遺傳信息。所以，這將再次受精 由不同的精子和。

we get back to a zygote. Where do we go from the zygote? We go right back here to mitosis

我們又回到了胚胎。我們從胚胎到哪裡去？我們回到這裡的有絲分裂

where we can copy that cell over and over and over and over again. And so that's cell

在那裡，我們可以複製該單元格一遍又一遍，一遍又一遍。所以這就是單元格

division. It's found in all cells on our planet. It shows how one cell can go to all the cells

分裂。它'在我們地球上的所有細胞中都能找到。它顯示了一個細胞如何去所有的細胞。

that we have to day. A good question might be where did that original cell come from?

我們有一天。一個很好的問題可能是，那個原始細胞從哪裡來？

But that's for another podcast. And I hope that was helpful.

但這'是另一個播客。我希望這是有幫助的。