The genes you don't get from your parents (but can't live without) - Devin Shuman

2,089,731 views ・ 2021-10-05

TED-Ed


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譯者: Lilian Chiu 審譯者: Amanda Zhu
00:07
Inside our cells, each of us has a second set of genes
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我們每個人的細胞中, 都還有第二組基因,
00:11
completely separate from the 23 pairs of chromosomes
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不包括在我們從父母遺傳 得到的二十三對染色體之內。
00:14
we inherit from our parents.
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00:16
And this isn’t just the case for humans—
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且不只有人類是如此,
00:18
it’s true of every animal, plant, and fungus,
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所有的動物、植物、真菌類,
00:22
and nearly every multicellular organism on Earth.
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以及地球上幾乎 所有的多細胞有機體也一樣。
00:26
This second genome belongs to our mitochondria,
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這第二組基因位在粒線體內,
00:30
an organelle inside our cells.
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粒線體是細胞中的一種胞器。
00:32
They’re not fully a part of us, but they’re not separate either—
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它們不完全是我們的一部分, 也不完全不是。
00:35
so why are they so different from anything else in our bodies?
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它們為什麼會如此不同於 我們體內的所有其他東西?
00:39
Approximately 1.5 billion years ago,
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科學家認為,
00:42
scientists think a single-celled organism engulfed the mitochondria’s ancestor,
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大約十五億年前,一種單細胞有機體
吞噬了粒線體的祖先,
00:48
creating the predecessor of all multicellular organisms.
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創造出了所有多細胞有機體的前身。
00:52
Mitochondria play an essential role:
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粒線體扮演了重要的角色:
00:54
they convert energy from the food we eat and oxygen we breathe
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我們吃的食物和吸的氧氣中的能量
00:58
into a form of energy our cells can use, which is a molecule called ATP.
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就要靠它們轉換成 細胞可以運用的能量形式,
即一種叫做三磷酸腺苷 ——即 ATP——的分子。
01:04
Without this energy, our cells start to die.
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沒有這種能量,細胞就會開始死亡。
01:07
Humans have over 200 types of cells,
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人類的細胞類型超過兩百種,
01:10
and all except mature red blood cells have mitochondria.
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除了成熟的紅血球細胞之外,
全部都有粒細體。
01:15
That’s because a red blood cell’s job is to transport oxygen,
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原因是紅血球細胞的 工作是在運送氧,
01:19
which mitochondria would use up before it could reach its destination.
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如果有粒細體在, 就會在抵達目的地前就把氧用光。
01:23
So all mitochondria use oxygen and metabolites to create energy
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所以,所有的粒線體
都會用氧和代謝產物來創造能量,
01:28
and have their own DNA,
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且擁有它們自己的 DNA,
01:31
but mitochondrial DNA varies more across species than other DNA.
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但粒線體 DNA 在不同物種間的差異性
比其他 DNA 更高。
01:36
In mammals, mitochondria usually have 37 genes.
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哺乳類動物的粒線體 通常有三十七個基因。
01:40
In some plants, like cucumbers, mitochondria have up to 65 genes,
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至於一些植物,如黃瓜,
其粒線體有高達六十五個基因,
01:46
and some fungal mitochondria have only 1.
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有些真菌類的粒線體則只有一個基因。
01:49
A few microbes that live in oxygen-poor environments
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少數幾種生活在稀氧環境中的微生物
01:53
seem to be on the way to losing their mitochondria entirely,
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幾乎快完全失去粒線體,
01:56
and one group, oxymonad monocercomonoides, already has.
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而有一類屬於類單鞭滴蟲屬的微生物,
已經沒有粒線體了。
02:02
This variety exists because mitochondria are still evolving,
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會有這樣的多樣性,
是因為粒線體仍然在演化,
02:06
both in tandem with the organisms that contain them,
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包括與它們所屬的有機體一起演化,
02:09
and separately, on their own timeline.
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以及依它們自己的時間表單獨演化。
02:11
To understand how that’s possible,
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要了解怎麼可能會如此,
02:13
it helps to take a closer look at what the mitochondria inside us are doing,
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可以先細究粒線體 在我們體內做些什麼,
02:18
starting from the moment we’re conceived.
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從懷孕的那一刻開始談起。
02:21
In almost all species, mitochondrial DNA is passed down from only one parent.
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幾乎所有物種的粒線體 DNA
都是由父母其中之一所傳下來。
02:27
In humans and most animals, that parent is the mother.
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就人類和大部分動物而言,是母親。
02:31
Sperm contain approximately 50 to 75 mitochondria in the tail,
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精子尾部含有大約 五十到七十五個粒線體,
02:35
to help them swim.
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用以協助它們游泳。
02:37
These dissolve with the tail after conception.
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受孕之後,這些粒線體 就會和尾部一起溶解。
02:40
Meanwhile, an egg contains thousands of mitochondria,
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一個卵子則含有數千個粒線體,
02:43
each containing multiple copies of the mitochondrial DNA.
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每個都含有多個粒線體 DNA。
02:47
This translates to over 150,000 copies of mitochondrial DNA
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算起來就有超過十五萬個粒線體 DNA
02:52
that we inherit from our mothers,
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都是來自我們的母親,
02:54
each of which is independent and could vary slightly from the others.
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每個粒線體都是獨立的, 且可能互相都有些微不同。
02:58
As a fertilized egg grows and divides,
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隨著受精卵成長和分裂,
03:01
those thousands of mitochondria are divvied up into the cells
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那數千個粒線體會分裂並分配到 發展中胚胎的各細胞當中,
03:04
of the developing embryo.
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03:06
By the time we have differentiated tissues and organs,
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當細胞已分化出組織和器官之後,
03:09
variations in the mitochondrial DNA are scattered at random throughout our bodies.
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粒線體 DNA 的差異
就會隨機散佈到我們全身各處。
03:15
To make matters even more complex,
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更複雜的是,
03:18
mitochondria have a separate replication process from our cells.
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粒線體和細胞的複製過程是分開的。
03:22
So as our cells replicate by dividing, mitochondria end up in new cells,
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所以,當細胞透過分裂來複製時,
粒線體就會進入到新的細胞中,
03:27
and all the while they’re fusing and dividing themselves,
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而在此過程中,粒線體 也一直依循著自己的時間表
03:30
on their own timeline.
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進行融合和分裂。
03:32
As mitochondria combine and separate,
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隨著粒線體結合和分離,
03:35
they sequester faulty DNA or mitochondria that aren’t working properly for removal.
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它們會把有缺陷、無法妥當運作的 DNA 或粒線體隔離並除去。
03:41
All this means that the random selection of your mother’s mitochondrial DNA
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也就是說,你在出生時 從母親身上隨機選擇
03:45
you inherit at birth
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而繼承的粒線體 DNA,
03:47
can change throughout your life and throughout your body.
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在你一生中、在你體內各處 都有可能會改變。
03:52
So mitochondria are dynamic and, to a degree, independent,
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所以粒線體會不斷變化, 某種程度上也是獨立的,
03:56
but they’re also shaped by their environments: us.
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但它們的環境,即我們, 也會改變它們。
03:59
We think that long ago,
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我們認為,很久以前,
04:01
some of their genes were transferred to their host’s genomes.
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它們的一些基因 被轉移給其宿主的基因組。
04:04
So today, although mitochondria have their own genome
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所以現今雖然粒線體 有它們自己的基因組,
04:08
and replicate separately from the cells that contain them,
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且複製過程和它們 所屬的細胞是分開的,
04:11
they can't do this without instruction from our DNA.
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沒有我們 DNA 的指示, 它們也無法複製。
04:15
And though mitochondrial DNA is inherited from one parent,
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且雖然粒線體 DNA 來自父母其中之一,
04:18
the genes involved in building and regulating the mitochondria
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用來建造和管理粒線體的基因
04:22
come from both.
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則是來自雙親。
04:23
Mitochondria continue to defy tidy classification.
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粒線體始終無法井然有序地分類。
04:27
Their story is still unfolding inside of each of our cells,
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存在於我們每個細胞裡的粒線體 仍有許多待解的謎團,
04:31
simultaneously separate and inseparable from our own.
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它們的故事和我們對人體的了解 是既分離又無法分離的。
04:35
Learning more about them can both give us tools
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進一步了解它們,一方面 能讓我們保護未來人類的健康,
04:37
to protect human health in the future, and teach us more about our history.
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二方面也能讓我們 更認識我們演化的歷史。
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