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

Translator: Magnus Chan Reviewer: Thomas Tam

Inside our cells, each of us has a second set of genes

喺我哋每個人嘅細胞內都有第二組基因

completely separate from the 23 pairs of chromosomes

跟父母遺傳嘅 23 對染色體唔同

we inherit from our parents.

And this isn’t just the case for humans—

呢啲唔淨止係人類

it’s true of every animal, plant, and fungus,

動物、植物、真菌同幾乎喺地球上

and nearly every multicellular organism on Earth.

所有嘅多細胞生物都係一樣有

This second genome belongs to our mitochondria,

第二組基因係屬於我哋嘅線粒體

an organelle inside our cells.

喺細胞內嘅細胞器

They’re not fully a part of us, but they’re not separate either—

佢哋唔係完全我哋嘅一部分 但亦都無分開過

so why are they so different from anything else in our bodies?

為乜佢跟我哋體內其他嘢區別咁大呢？

Approximately 1.5 billion years ago,

大概喺 1.5 億年前

scientists think a single-celled organism engulfed the mitochondria’s ancestor,

科學家認為有個單細胞 把啲線粒體嘅祖先吞咗入去

creating the predecessor of all multicellular organisms.

創造咗所有多細胞生物嘅前身

Mitochondria play an essential role:

線粒體嘅角色唔可以抺殺

they convert energy from the food we eat and oxygen we breathe

佢哋將人嘅食物同氧氣所產生嘅能量

into a form of energy our cells can use, which is a molecule called ATP.

轉換成我哋細胞能夠使用嘅能量 一種名為 ATP 嘅分子

Without this energy, our cells start to die.

無呢種能量我哋嘅細胞就會開始死

Humans have over 200 types of cells,

人類有超過 200 種不同嘅細胞

and all except mature red blood cells have mitochondria.

除咗成熟嘅紅細胞之外，全部都有線粒體

That’s because a red blood cell’s job is to transport oxygen,

理由係紅細胞嘅工作係傳送氧氣

which mitochondria would use up before it could reach its destination.

否則紅細胞嘅氧氣 喺未到達目的地就畀線粒體用完

So all mitochondria use oxygen and metabolites to create energy

總結一下，所有線粒體 係用氧氣同代謝物去產生能量

and have their own DNA,

同埋有自己嘅基因

but mitochondrial DNA varies more across species than other DNA.

但嗰啲喺不同物種嘅線粒體基因 比起其他嘅基因分別更大

In mammals, mitochondria usually have 37 genes.

喺哺乳類動物，線粒體通常有 37 個基因。

In some plants, like cucumbers, mitochondria have up to 65 genes,

有啲植物比如青瓜 線粒體有高達 65 個基因

and some fungal mitochondria have only 1.

然而有啲真菌只有 1 個基因

A few microbes that live in oxygen-poor environments

有幾種生活喺缺氧環境嘅微生物

seem to be on the way to losing their mitochondria entirely,

似乎正喺度喪失所有線粒體

and one group, oxymonad monocercomonoides, already has.

同時有個組別，氧化單胞菌 已經完全喪失線粒體

This variety exists because mitochondria are still evolving,

呢種多樣性之所以存在 係因為綫粒體仍在進化緊

both in tandem with the organisms that contain them,

既與含有綫粒體嘅生物一起進化

and separately, on their own timeline.

又單獨地按照自己嘅時間綫

To understand how that’s possible,

要了解係點樣可能

it helps to take a closer look at what the mitochondria inside us are doing,

仔細睇下喺我哋體內線粒體喺度做啲乜嘢

starting from the moment we’re conceived.

可由我哋懷孕嗰刻講起

In almost all species, mitochondrial DNA is passed down from only one parent.

喺幾乎所有嘅物種 線粒體基因只係從父母其中一人傳落嚟

In humans and most animals, that parent is the mother.

喺人類同大部分嘅動物 就只係母親

Sperm contain approximately 50 to 75 mitochondria in the tail,

喺精子尾巴中 大概有 50 到 75 個線粒體

to help them swim.

幫助精子游動

These dissolve with the tail after conception.

佢哋喺受精之後 會跟尾巴一同溶解

Meanwhile, an egg contains thousands of mitochondria,

與此同時，一隻卵子有數千個線粒體

each containing multiple copies of the mitochondrial DNA.

每個卵子都包含好多份佢哋嘅基因複製系列

This translates to over 150,000 copies of mitochondrial DNA

等於有超過 150,000 線粒體基因嘅複製本

that we inherit from our mothers,

係從母親遺傳落嚟嘅

each of which is independent and could vary slightly from the others.

而每個複製本都係獨立嘅 跟其他有少許分別

As a fertilized egg grows and divides,

受咗精嘅卵子喺度生長同分裂

those thousands of mitochondria are divvied up into the cells

嗰數千個線粒體 會分開進入胚胎中不同嘅細胞

of the developing embryo.

By the time we have differentiated tissues and organs,

當我哋身體分化出唔同嘅組織同器官

variations in the mitochondrial DNA are scattered at random throughout our bodies.

變異嘅線粒體基因會隨機分佈喺身體各處

To make matters even more complex,

令到整件事更加複雜啲

mitochondria have a separate replication process from our cells.

線粒體有自己嘅複製過程 跟我哋嘅細胞唔同

So as our cells replicate by dividing, mitochondria end up in new cells,

因此喺我哋細胞複製嘅時候 線粒體會去咗不同嘅新細胞

and all the while they’re fusing and dividing themselves,

與此同時，線粒體自己 亦跟著自己嘅時間線喺度合成同埋分裂

on their own timeline.

As mitochondria combine and separate,

當線粒體合成同分裂嘅時候

they sequester faulty DNA or mitochondria that aren’t working properly for removal.

會分隔出有缺陷嘅基因 同唔正常運作嘅線粒體

All this means that the random selection of your mother’s mitochondrial DNA

一切都意味住，喺你出生時 繼承母親隨機選擇嘅線粒體基因

you inherit at birth

can change throughout your life and throughout your body.

會喺你一生度結合整個身體產生變化

So mitochondria are dynamic and, to a degree, independent,

所以線粒體係動態嘅 而且某程度上係獨立嘅

but they’re also shaped by their environments: us.

但佢哋亦受到周邊環境 即係我哋身體嘅影響

We think that long ago,

好久以前

some of their genes were transferred to their host’s genomes.

一啲線粒體嘅基因 被轉移到宿主嘅基因組度

So today, although mitochondria have their own genome

現在雖然線粒體有自己嘅基因組

and replicate separately from the cells that contain them,

係跟包含佢哋嘅細胞，分開嚟自我複製

they can't do this without instruction from our DNA.

但佢哋喺無基因嘅指令下 唔能夠自己進行複製

And though mitochondrial DNA is inherited from one parent,

雖然線粒體基因係從母親遺傳落嚟

the genes involved in building and regulating the mitochondria

但參與建造同埋調控線粒體嘅基因

come from both.

係從父母遺傳

Mitochondria continue to defy tidy classification.

線粒體係繼續抗拒整整齊齊咁分類

Their story is still unfolding inside of each of our cells,

佢哋嘅故事係，繼續喺我哋每個細胞裏邊

simultaneously separate and inseparable from our own.

分離作業，又與細胞密不可分

Learning more about them can both give us tools

更了解線粒體會給我哋工具

to protect human health in the future, and teach us more about our history.

去保護人類未來嘅健康 同教育我哋自己嘅歷史