Mitochondria are the powerhouse of the cell.

線粒體是細胞的動力源。

I know, I know.

我知道，我知道。

But cliches become cliches for a reason.

但陳詞濫調成為陳詞濫調是有原因的。

It's usually because they're the easiest way to say something.

這通常是因為它們是最簡單的表達方式。

For better or for worse.

是好是壞

Oh no, that's another one!

哦，不，又是一個！

In this case, mitochondria really are the powerhouse of the cell.

在這種情況下，線粒體確實是細胞的動力源。

These little organelles inside of all of your trillions of cells are hard at work transferring energy from food and oxygen into the fuel you need to do everything from texting a friend to organizing your stuffed insect collection.

從給朋友發短信到整理你的昆蟲毛絨玩具，你所有數以萬億計的細胞內的這些小細胞器都在努力工作，將食物和氧氣中的能量轉移為你所需的燃料。

I mean, clearly you can't put the praying mantis next to the moth!

我的意思是，顯然不能把螳螂放在飛蛾旁邊！

Mitochondria are a key player in cellular respiration, the process that breaks down food and oxygen so that we can energize our cells.

線粒體是細胞呼吸的關鍵角色，細胞呼吸是分解食物和氧氣的過程，從而為細胞提供能量。

And we often take cellular respiration for granted.

我們常常認為細胞呼吸是理所當然的。

After all, it goes on behind the scenes, totally escaping our notice.

畢竟，這一切都在幕後進行，完全沒有引起我們的注意。

But it's an important process for all of us multicellular, oxygen-breathing organisms.

但對於我們這些多細胞、呼吸氧氣的生物來說，這是一個重要的過程。

Hi, I'm Dr. Sammy, your friendly neighborhood entomologist, and this is Crash Course Biology.

大家好，我是山米博士，你們身邊的昆蟲學家，這裡是生物速成班。

Breathe in that fresh theme music.

呼吸新鮮的主題音樂

INTRO Energy in our bodies is stored in the molecule ATP, or adenosine triphosphate.

導言 人體內的能量儲存在三磷酸腺苷（ATP）分子中。

ATP is like a rechargeable battery, we fill it with energy again and again.

ATP 就像一個可充電電池，我們一次又一次地為它注入能量。

And the energy is used to power important cellular processes, like making sure our bodies maintain homeostasis, or in other words, keeping our bodies regulated with the right balance of the stuff that we need.

這些能量被用來驅動重要的細胞過程，比如確保我們的身體保持平衡，或者換句話說，保持我們身體所需的各種物質的平衡。

This is what keeps us functioning relatively stably even as the conditions around us change, like when we sweat to get rid of extra heat energy, or shiver to generate more heat.

是以，即使周圍環境發生變化，我們也能保持相對穩定的運作，比如我們出汗以排出多餘的熱能，或顫抖以產生更多的熱量。

The average human needs to use over 100 pounds of ATP a day.

人類平均每天需要消耗 100 多磅的 ATP。

A hundred pounds, though?

一百英鎊？

That's a lot.

太多了

That's a huge amount.

這是一個巨大的數字。

That is my body weight, basically, in ATP.

這就是我的體重，基本上是 ATP。

Okay, no, no, I'm good.

好吧，不，不，我很好。

I'm good.

我很好

I'm fine.

我沒事

I just, you know, mind blown.

我只是，你知道的，心靈受到了震撼。

Now we gotta put it back together so I can do the show.

現在我們得把它重新組裝起來，這樣我就能做節目了。

But like money, ATP doesn't grow on trees.

但就像金錢一樣，ATP 也不是從樹上長出來的。

Our bodies need to be constantly making and breaking down ATP in a recycling process that amounts to a full-time job for our cells.

我們的身體需要不斷製造和分解 ATP，這一循環過程對細胞來說是一項全職工作。

That job?

那份工作？

Cellular respiration.

細胞呼吸

See, you, me, and all the bugs, birds, and fish between us are aerobic organisms, which basically means we need oxygen to live and grow.

你看，你、我以及我們中間的所有蟲子、鳥類和魚類都是需氧生物，這基本上意味著我們需要氧氣來生存和生長。

And with the help of that oxygen, our cells release energy from our food and store it in the form of ATP.

在氧氣的幫助下，我們的細胞從食物中釋放能量，並以 ATP 的形式儲存起來。

But there are also organisms, such as some bacteria, that can release and store energy without oxygen in a process called anaerobic respiration.

但也有一些生物，例如一些細菌，可以在沒有氧氣的情況下釋放和儲存能量，這個過程被稱為無氧呼吸。

And you have fermentation, a similar process that doesn't require oxygen, to thank for sourdough, kombucha, and kimchi.

發酵是一種不需要氧氣的類似過程，酸麵糰、昆布茶和泡菜都要歸功於發酵。

In any case, the cellular respiration process is sort of like a million tiny little fires burning inside of each of your cells.

無論如何，細胞呼吸過程就像是無數個小火苗在你的每個細胞內燃燒。

Glucose and oxygen are the fuel in this process, coming from the air that you breathe and the food that you eat, especially carbohydrates.

在這一過程中，葡萄糖和氧氣是燃料，它們來自呼吸的空氣和攝入的食物，尤其是碳水化合物。

And carbon dioxide and water are the end products.

二氧化碳和水是最終產物。

Unlike a campfire, where the carbohydrates and wood burn up quickly to give off energy as heat and light, the process of breaking down food by cellular respiration releases energy relatively slowly through many chemical reactions.

與篝火不同的是，篝火中的碳水化合物和木材會迅速燃燒，以光和熱的形式釋放能量，而細胞呼吸分解食物的過程則通過許多化學反應相對緩慢地釋放能量。

Cells do this in a controlled way so that the energy is harvested to assemble ATP molecules instead of, like, you know, an explosion.

細胞以一種可控的方式完成這一過程，這樣獲得的能量是用來組裝 ATP 分子，而不是像爆炸那樣。

Yeah, as cool as it sounds, a little fire in your belly would be counterproductive by evolutionary standards.

是啊，雖然聽起來很酷，但從進化的標準來看，肚子裡有點火會適得其反。

Cellular respiration combines a couple of metabolic pathways, or linked chemical reactions, that happen in cells to complete a process.

細胞呼吸結合了細胞內發生的幾種代謝途徑或相關化學反應，以完成一個過程。

You can think of it like a Rube Goldberg machine, where one chemical reaction triggers the next, and then that one starts the next one, and so on.

你可以把它想象成一臺魯布-戈德堡（Rube Goldberg）機器，一個化學反應引發下一個化學反應，然後這個化學反應又引發下一個化學反應，以此類推。

The whole process needs a jumpstart of ATP to get going.

整個過程需要 ATP 來啟動。

But eventually, at the end of cellular respiration, more ATP is produced than was needed at the start.

但最終，在細胞呼吸結束時，產生的 ATP 會多於開始時所需的 ATP。

It's true what they say, you gotta spend money to make money.

俗話說得好，要賺錢就得花錢。

So, okay, how does this remarkable system happening all the time within each of our cells actually work?

那麼，我們每個細胞中一直存在的這一非凡系統究竟是如何運作的呢？

Cellular respiration occurs in three main stages.

細胞呼吸主要分為三個階段。

It all starts with glycolysis, which breaks down the simple sugar glucose that we get from eating carbs.

這一切都始於糖酵解，它能分解我們從碳水化合物中獲得的單糖葡萄糖。

See, glucose doesn't help us much in this form.

看，葡萄糖在這種形式下對我們幫助不大。

It's not the right energy currency for the cell.

對細胞來說，這不是合適的能量貨幣。

The cell's energy you exchange it.

細胞的能量由你來交換。

Shout out to Catherine Fontana, one of the former students from my science communication class, for this analogy.

這個比喻要感謝凱瑟琳-方塔納（Catherine Fontana），她是我以前科學傳播課的學生之一。

Glycolysis is the first part of that system of currency exchange, and it happens in a cell's cytoplasm, the jello-like goo that fills it up.

糖酵解是貨幣交換系統的第一部分，它發生在細胞的細胞質中，也就是充滿細胞的果凍狀粘液中。

See, ten different enzymes, you can think of them like little bank tellers, catalyze or speed up ten chemical reactions to break down the glucose.

看，十種不同的酶，你可以把它們想象成小銀行出納員，催化或加速十個化學反應來分解葡萄糖。

Each one makes a small change to the currency, and hands it off to the next teller, with the last of them yielding a 3-carbon chemical called pyruvate, an important transition molecule that becomes the key reactant in further processes like the citric acid cycle or anaerobic respiration.

每個人都會給貨幣找一點零錢，然後把它交給下一個出納員，最後一個出納員得到一種叫做丙酮酸的 3 碳化學物質，這是一種重要的過渡分子，在檸檬酸循環或無氧呼吸等進一步的過程中成為關鍵的反應物。

Glycolysis results in the net production of two molecules of our target currency ATP, and it also relies on a molecule called NAD+, which you can think of as a carrier molecule.

糖酵解的結果是淨產生兩分子目標貨幣 ATP，它還依賴於一種叫做 NAD+ 的分子，你可以將其視為載體分子。

Here at the First National Bank of the Cell, we've got these fancy proton and electron coins that can be exchanged later for even more ATP.

在細胞第一國家銀行，我們有這些精美的質子和電子硬幣，可以在以後兌換更多的 ATP。

For safekeeping, right now we'll just attach them to this molecule of NAD+.

為了安全起見，現在我們只把它們連接到這個 NAD+ 分子上。

At the end of stage 1, it hauls off two electrons and one proton to form NADH, which is used in the final step of cellular respiration.

在第一階段結束時，它會帶走兩個電子和一個質子，形成 NADH，用於細胞呼吸的最後一步。

But let's not put the cart before the horse.

但我們不能本末倒置。

Once glycolysis has finished, we begin the prep work for stage 2, which will be the citric acid cycle.

糖酵解完成後，我們開始第二階段的準備工作，即檸檬酸循環。

Our pyruvate reactant moves from the cell's cytoplasm into the mitochondria.

丙酮酸反應物從細胞質進入線粒體。

Here, an enzyme continues to process the pyruvate, mining it for even more energy.

在這裡，一種酶會繼續處理丙酮酸，挖掘出更多的能量。

It oxidizes the molecule, basically plucking another pair of electron coins from it to be used later on.

它使分子氧化，基本上就是從分子中獲取了另一對電子硬幣，以便日後使用。

This step is where some of the carbon dioxide that's produced by cellular respiration gets made.

細胞呼吸產生的部分二氧化碳就是在這個步驟中生成的。

A CO2 molecule, which we exhale, splits off of the pyruvate and leaves behind a product with just two carbons.

我們呼出的二氧化碳分子會從丙酮酸中分離出來，留下只有兩個碳原子的產物。

And this new two-carbon product kickstarts the next metabolic pathway involved in respiration, the citric acid cycle, also called the Krebs cycle.

這種新的兩碳產物啟動了呼吸作用的下一個代謝途徑--檸檬酸循環，也稱為克雷布斯循環。

Now, when this two-carbon molecule bonds with this four-carbon molecule, oxaloacetate, they make a product with six carbons.

現在，當這個兩碳分子與這個四碳分子（草酰乙酸）結合時，它們會生成一個六碳的產物。

It's a complicated, multi-step process.

這是一個複雜的、多步驟的過程。

But long story short, a couple enzymes come along and remove two of those carbons to make two more carbon dioxide molecules, which again, we exhale.

不過，長話短說，有幾種酶會將其中的兩個碳移除，再生成兩個二氧化碳分子，然後我們再次將其呼出。

I mean, we're just giving the stuff away at this point.

我是說，我們現在只是在送東西。

Alongside the carbon dioxide, the citric acid cycle also produces one more ATP, three more molecules of NADH, and another transport molecule for electrons and protons called FADH2.

除二氧化碳外，檸檬酸循環還能產生一個 ATP、三個 NADH 分子以及另一個名為 FADH2 的電子和質子傳輸分子。

The citric acid cycle is, well, a cycle.

檸檬酸循環就是一個循環。

So in the end, we're back to a chemical with four carbons, this exact same four-carbon molecule that we started with.

最後，我們又回到了一個有四個碳的化學物質，這個和我們開始時一模一樣的四碳分子。

Then the four-carbon molecule bonds with the next incoming two-carbon molecule, and the cycle continues.

然後，四碳分子與下一個進入的二碳分子結合，循環往復。

It happens twice for every glucose molecule that kickstarts cellular respiration.

每個啟動細胞呼吸的葡萄糖分子都會發生兩次這種情況。

Which brings us to the final step in cellular respiration, stage three, oxidative phosphorylation.

這就是細胞呼吸的最後一步，第三階段，氧化磷酸化。

This also occurs in the where the bulk of ATP gets made.

這也發生在製造大部分 ATP 的地方。

If the first two stages of this process were like visiting the bank, oxidative phosphorylation is like going to the mint where the money is printed.

如果說這個過程的前兩個階段就像是去銀行，那麼氧化磷酸化就像是去印鈔票的造幣廠。

See, mitochondria have a really neat structure that makes all of this possible.

你看，線粒體有一個非常整齊的結構，使這一切成為可能。

There's an outer membrane containing large pores that can let chemicals in and out, and there's a second membrane folded up inside of it.

有一層外膜，內含可讓化學物質進出的大孔，還有一層膜摺疊在它的內部。

Stuck into the inner membrane, we find the huge protein complexes of the electron transport chain, which have two jobs.

在內膜中，我們發現了電子傳遞鏈的巨大蛋白質複合體，它們有兩項工作。

One is to accept the electrons from the transport molecules when they make a stop at the very inside of both membranes.

其一是當運輸分子在兩層膜的最裡面停留時，接受它們的電子。

After they're dropped off, the electrons travel through the electron transport chain, where each acceptor in the pathway forms a more stable molecule than the one before it when it takes electrons.

電子脫落後，通過電子傳遞鏈，途徑中的每個受體在接受電子時都會形成比前一個更穩定的分子。

So each step releases energy.

是以，每一步都會釋放能量。

The chemical energy gets turned into mechanical energy that lets the protein complexes of the electron transport chain do their second job, proton pumping.

化學能轉化為機械能，讓電子傳遞鏈的蛋白質複合體完成第二項工作--質子泵。

Those protons that got dropped off in the matrix have somewhere that they're needed, the intermembrane space, which is what it sounds like, the space between the inner and outer mitochondrial membranes.

那些掉落在基質中的質子有了用武之地，那就是膜間隙，聽起來就是線粒體內膜和外膜之間的空間。

And the energy that's released as the electrons move through the electron transport chain is what sends them there.

電子在電子傳遞鏈中移動時釋放的能量就是將它們送到那裡的動力。

So the protons get actively transported as a result of the energy released from the process before.

是以，質子在之前的過程中釋放出的能量會使質子得到主動運輸。

Proton pumping then puts a bunch of the concentration.

然後，質子泵會將大量的能量集中起來。

This creates a proton gradient where the amount of protons is way higher between the membranes than in the matrix.

這就形成了質子梯度，膜之間的質子量遠遠高於基質中的質子量。

Think of it like a dam.

把它想象成水壩。

One side of the dam is filled with a lot more water than the other.

大壩一側的水比另一側多很多。

And if we open a channel, the water from the full side comes rushing in with some serious force.

如果我們打開一條通道，水就會以巨大的力量從另一側湧入。

And this can be used to generate electricity by moving hydroelectric generators.

這可以通過移動水力發電機來發電。

It's the same for the concentrated protons in the intermembrane space.

膜間隙中的濃縮質子也是如此。

The protons have a path back into the matrix through a channel in the form of an enzyme called ATP synthase.

質子可以通過一種名為 ATP 合酶的酶的形式返回基質。

Resembling a flower, the ATP synthase stalk is planted within the inner mitochondrial membrane.

ATP 合成酶柄就像一朵花，種植在線粒體內膜上。

Protons enter a channel on the intermembrane space side and pass back into the matrix moving from high concentration to low concentration in an attempt to even the proton gradient out.

質子進入膜間隙一側的通道，然後返回基質，從高濃度向低濃度移動，以平衡質子梯度。

The proton movement pushes ATP synthase like a merry-go-round, providing the power that literally spins the ATP synthase like the water rushing through a dam powers a hydroelectric generator to create electricity.

質子運動像旋轉木馬一樣推動 ATP 合成酶，為 ATP 合成酶的旋轉提供動力，就像水流通過大壩為水力發電機發電提供動力一樣。

The rotation causes movement up the whole stalk of ATP synthase.

旋轉導致 ATP 合酶的整個柄向上移動。

In this final stage of cellular respiration, the movement of protons powers the ATP synthase, which instead of making electricity, makes a ton of ATP, around 30 molecules for each glucose molecule that we start with.

在細胞呼吸的最後階段，質子的運動為 ATP 合酶提供動力，它不是發電，而是製造大量的 ATP，每一個葡萄糖分子大約能製造 30 個分子。

So all together, one glucose molecule has an exchange rate of about 30 ATP.

是以，總的來說，一個葡萄糖分子的交換率約為 30 ATP。

And all of those remaining electrons when they're passed through the electron transport chain?

而所有這些剩餘的電子在通過電子傳遞鏈時呢？

Well, they ultimately get passed on to two bonded oxygen atoms, and to balance the negative charges that the bonded oxygen atoms accept as electrons, they have to grab some protons too, forming our old friend water.

那麼，它們最終會傳遞給兩個結合在一起的氧原子，為了平衡結合在一起的氧原子所接受的電子負電荷，它們還必須抓住一些質子，形成我們的老朋友水。

So I know that's a lot of information.

所以我知道信息量很大。

Let's take a moment to Glycolysis takes glucose from the food you eat and produces pyruvate, along with a little ATP and NADH, starting the process of currency exchange.

讓我們花一點時間來了解一下糖酵解，它從食物中提取葡萄糖，產生丙酮酸以及少量的 ATP 和 NADH，開始貨幣交換過程。

The pyruvate moves into the mitochondria where it gets oxidized, shortening it to a two-carbon chemical.

丙酮酸進入線粒體，在那裡被氧化，縮短為雙碳化學物質。

That chemical enters the citric acid cycle, where enzymes further break it down, producing the carbon dioxide that we exhale, plus a little more ATP and NADH.

這種化學物質進入檸檬酸循環，在這裡酶進一步將其分解，產生我們呼出的二氧化碳，以及更多的 ATP 和 NADH。

And while all of that is happening, the electrons and protons in the form of hydrogen atoms that are being removed during each step are hitching a ride into the mitochondria through the transport molecules NADH and FADH2.

而在這一切發生的同時，在每個步驟中被移除的氫原子形式的電子和質子正通過運輸分子 NADH 和 FADH2 搭便車進入線粒體。

The electrons provide the energy to move protons, creating a gradient that is constantly searching for an equilibrium.

電子為質子的移動提供能量，從而形成一個不斷尋求平衡的梯度。

All the while, the leftover electrons hitch their wagons to oxygen and create water.

同時，剩餘的電子與氧氣結合，生成水。

As the protons move into the mitochondrial matrix, their movement powers the ATP synthase, which in turn creates a bunch of molecules of ATP.

當質子進入線粒體基質時，它們的運動為 ATP 合酶提供動力，而 ATP 合酶又會產生大量的 ATP 分子。

And that ATP being generated inside the mitochondria then powers all of our other cellular processes.

線粒體內產生的 ATP 將為我們所有其他的細胞過程提供能量。

And what's even wilder is that all of that is happening not only constantly, but really, really quickly.

更令人驚奇的是，這一切不僅在不斷髮生，而且發生得非常非常快。

Sure, it's slow compared to the reactions in a fire or an explosion, but it's really fast by human standards.

當然，與火災或爆炸中的反應相比，它是緩慢的，但以人類的標準來看，它確實很快。

What took me a whole episode to explain happens in the blink of an eye.

我花了一整集的時間來解釋的事情，轉眼間就發生了。

Around 10 million ATP molecules can be generated per second in a single cell.

單個細胞每秒可生成約 1 千萬個 ATP 分子。

Speaking of explosions, my mind was just blown.

說到爆炸，我的腦子裡一片空白。

The process of cellular respiration is like many cellular processes, a complex one.

細胞呼吸過程與許多細胞過程一樣，是一個複雜的過程。

But it's also an incredibly important one.

但這也是一個非常重要的問題。

It generates the ATP molecules that we use to run these complicated machines we call bodies.

它產生的 ATP 分子用於運行我們稱之為身體的複雜機器。

And to do that, cliches aside, we need the mitochondria, the powerhouse of the cell.

要做到這一點，拋開陳詞濫調不談，我們需要線粒體這個細胞的動力源。

Without those little organelles inside all of our cells, we would be in a bad way.

如果沒有細胞內的這些小細胞器，我們就會陷入困境。

So thanks, mitochondria, for keeping us grooving.

所以，謝謝你，線粒體，讓我們繼續狂歡。

Next time, we're going to dive into what is arguably the most important chemical reaction on Earth.

下一次，我們將深入探討地球上最重要的化學反應。

I'm talking about photosynthesis.

我說的是光合作用。

But we'll cross that bridge when we get there.

不過，我們到時再過橋吧。

I'll see you then.

到時候見

Deuces!

Deuces！

This series was produced in collaboration with HHMI BioInteractive.

本系列由 HHMI BioInteractive 合作製作。

If you're an educator, visit biointeractive.org slash crash course for classroom resources and professional development related to the topics covered in this course.

如果您是教育工作者，請訪問 biointeractive.org slash crash course，獲取與本課程所涉及主題相關的課堂資源和專業發展。

Thanks for watching this episode of Crash Course Biology, which was filmed at our studio in Indianapolis, Indiana, and was made with the help of all of these nice people.

感謝您收看本期《生物學速成班》，本期節目是在我們位於印第安納州印第安納波利斯的工作室拍攝的，是在這些好心人的幫助下製作完成的。

If you want to help keep Crash Course free for everyone, forever, you can join our community on Patreon.

如果您想幫助《速成課程》永遠免費，可以加入我們的 Patreon 社區。