Nature's smallest factory: The Calvin cycle - Cathy Symington

譯者: Regina Chu 審譯者: Marssi Draw

You're facing a giant bowl

你對著滿滿一大碗的

of energy packed Carbon Crunchies.

活力碳素早餐脆片

One spoonful. Two. Three.

一匙、二匙、三匙

Soon, you're powered up by the energy surge

很快你就會因為你吃的餐點

that comes from your meal.

能量飆升，充滿活力

But how did that energy get into your bowl?

但是能量如何進到你的碗內？

Energy exists in the form of sugars

能量以糖的形式存在

made by the plant your cereal came from,

糖又從製成早餐榖片的植物而來

like wheat or corn.

如小麥或玉米

As you can see, carbon is the chemical backbone,

如你所見，碳是化學骨架

and plants get their fix of it

而植物從我們呼吸的空氣中

in the form of carbon dioxide, CO2,

以二氧化碳 CO2 的形式

from the air that we all breath.

取得碳

But how does a plant's energy factory,

但位於葉綠體基質中的

housed in the stroma of the chloroplast,

植物能量工廠

turn a one carbon gas, like CO2,

如何將單碳氣體如二氧化碳

into a six carbon solid, like glucose?

轉變成六碳固體如葡萄糖？

If you're thinking photosynthesis, you're right.

如果你想到光合作用，你就對了

But photosynthesis is divided into two steps.

但光合作用又分成兩個步驟

The first, which stores energy from the sun

第一步，把光能

in the form of adenosine triphosphate, or ATP.

以三磷酸腺苷 ATP 形式儲存起來

And the second, the Calvin cycle, that captures carbon

第二步，卡爾文循環捕捉碳

and turns it into sugar.

並將之轉成糖

This second phase represents one of nature's

這第二階段代表了大自然

most sustainable production lines.

最永續的生產線

And so with that, welcome to world's most miniscule factory.

因此，歡迎蒞臨世界最袖珍的工廠

The starting materials?

起始材料？

A mix of CO2 molecules from the air,

空氣中的二氧化碳分子

and preassembled molecules called

混合預先裝配好的分子

ribulose biphosphate, or RuBP,

稱為核酮糖-1,5-二磷酸，簡稱 RuBP

each containing five carbons.

每一個分子都含五個碳

The initiator? An industrious enzyme named rubisco

催化劑？一種勤奮的酵素 rubisco （二磷酸核酮糖羧化酶）

that welds one carbon atom from a CO2 molecule

它將二氧化碳分子中的一個碳原子

with the RuBP chain

接到 RuBP 鏈上

to build an initial six carbon sequence.

產生最初為六碳的序列

That rapidly splits into two shorter chains

然後急速地分裂成兩個較短的鏈

containing three carbons each

各含三個碳

and called phosphoglycerates, or PGAs, for short.

稱為3-磷酸甘油酸 或簡稱為 PGA

Enter ATP, and another chemical called

ATP 及另一種化合物進入，稱做

nicotinamide adenine dinucleotide phosphate,

菸草醯胺腺嘌呤二核苷酸磷酸鹽

or just NADPH.

或就叫 NADPH

ATP, working like a lubricant, delivers energy,

ATP 的功用就像潤滑劑，輸送能量

while NADPH affixes one hydrogen to each of the PGA chains,

而 NADPH 在每個 PGA 鏈上加一個氫

changing them into molecules called

將 PGA 轉變成另一種稱為

glyceraldehyde 3 phosphates, or G3Ps.

甘油醛3-磷酸的分子，簡稱 G3P

Glucose needs six carbons to form,

形成葡萄糖需要六個碳

made from two molecules of G3P,

以兩個 G3P 分子製成

which incidentally have six carbons between them.

而這種結合剛好有六個碳

So, sugar has just been manufactured, right?

所以，糖就這麼製成了，是嗎？

Not quite.

還沒有

The Calvin cycle works like a sustainable production line,

卡爾文循環就像一條永續生產線

meaning that those original RuBPs

也就是說那些原有的 RuBP

that kicked things off at the start,

在循環開始時啟動反應的物質

need to be recreated by reusing materials

需要以重複利用

within the cycle now.

此循環中的物質來再生

But each RuBP needs five carbons

但是每一個 RuBP 都要五個碳

and manufacturing glucose takes a whole six.

而製造葡萄糖要六個碳

Something doesn't add up.

這怎麼湊得起來呢？

The answer lies in one phenomenal fact.

答案就在一項驚人事實裡

While we've been focusing on this single production line,

就在我們專心在這條單向生產線時

five others have been happening at the same time.

另外五條生產線也同時開工

With six conveyor belts moving in unison,

總共六條輸送帶聯袂作用

there isn't just one carbon that gets soldered

所以並不是僅加一個碳

to one RuBP chain,

到一個 RuBP 鏈上

but six carbons soldered to six RuBPs.

而是接了六個碳到六個 RuBP 上

That creates 12 G3P chains instead of just two,

這樣就產生了 12 個 G3P 鏈 而不是僅僅 2 個

meaning that all together, 36 carbons exist:

意思是加起來共有 36 個碳存在

the precise number needed to manufacture sugar,

正是製造（一個）糖 及重建（六個） RuBP

and rebuild those RuBPs.

所需要的數字

Of the 12 G3Ps pooled together,

在這匯集在一起的 12 個G3P 中

two are siphoned off to form

有兩個被抽掉用來形成

that energy rich six carbon glucose chain.

充滿能量的六碳葡萄糖鏈

The one fueling you via your breakfast. Success!

透過你的早餐幫你加油。成功！

But back on the manufacturing line,

但回到生產線

the byproducts of this sugar production

這條糖生產線的副產品

are swiftly assembled to recreate those six RuBPs.

瞬間組裝以再製六個 RuBP

That requires 30 carbons,

那需要 30 個碳

the exact number contained by the remaining 10 G3PS.

正是餘下的 10 個 G3P 所含的數字

Now a molecular mix and match occurs.

現在要開始分子混搭

Two of the G3Ps are welded together

兩個 G3P 要結合在一起

forming a six carbon sequence.

形成一個六碳序列

By adding a third G3P, a nine carbon chain is built.

再加上第三個 G3P 後 就製成了一條九碳鏈

The first RuBP, made up of five carbons,

由五個碳組成的第一個 RuBP

is cast from this,

就從這條九碳鏈中脫離

leaving four carbons behind.

留下四個碳

But there's no wastage here.

但物要盡其用

Those are soldered to a fourth G3P molecule,

這四個碳要加到第四個 G3P 分子上

making a seven carbon chain.

成為一條七碳鏈

Added to a fifth G3P molecule,

把其加到第五個 G3P 分子上

a ten carbon chain is created,

一條十碳鏈就產生了

enough now to craft two more RuBPs.

足夠再製作兩個 RuBP

With three full RuBPs recreated

十個 G3P 裡只要五個就能再製

from five of the ten G3Ps,

三個完整的 RuBP

simply duplicating this process

只要再重複這個製程

will renew the six RuBP chains

就能重生六個 RuBP 鏈

needed to restart the cycle again.

供給重新啟動整個循環所需

So the Calvin cycle generates the precise number

所以卡爾文循環生成

of elements and processes

確切數量的原件和流程

required to keep this biochemical production line

能讓這個生化生產線

turning endlessly.

無休止運轉

And it's just one of the 100s of cycles

而這僅是存在於自然界中

present in nature.

上百個循環之一

Why so many?

為什麼要這麼多循環？

Because if biological production processes were linear,

因為如果生物生產流程是線性的

they wouldn't be nearly as efficient or successful

就不會這麼有效率及成功的

at using energy to manufacture the materials

使用能量來製造

that nature relies upon, like sugar.

自然界仰賴的物質，如糖

Cycles create vital feedback loops

各式循環產生重要的維生回饋圈

that repeatedly reuse and rebuild ingredients

回饋圈儘可能

crafting as much as possible

從地球的可用資源中精密製造

out of the planet's available resources.

能不斷重覆利用及重建的材料

Such as that sugar,

就像糖一樣

built using raw sunlight and carbon

靠著使用原始的陽光及碳

converted in plant factories

將其在植物工廠內轉變

to become the energy that powers you

成為供給你動力的能量

and keeps the cycles revolving in your own life.

並讓你生命中的各式循環繼續運轉