thousands of chemical reactions are taking place.

數以千計的化學反應正在發生。

These reactions are

這些反應是

performed by enzymes. An enzyme is a

由酶進行。酶是一種

protein that catalyzes a chemical reaction.

催化化學反應的蛋白質。

It initiates the reaction,

它引發反應，

speeds up the reactions progress, and

加快反應進程，並且

makes sure the outcome is always the same.

確保結果始終如一。

These enzymes often work together to

這些酶經常一起工作

form longer pathways, such as the

形成更長的途徑，如

Citric Acid Cycle, which is a series of

檸檬酸循環，這是一系列的

chemical reactions used by cells to generate

細胞產生的化學反應

energy from carbohydrates.

碳水化合物的能量。

The essential tasks of life such as metabolism,

生命的基本任務，如新陳代謝，

protein synthesis, and cell renewal and growth

蛋白質合成，細胞更新和生長

are all regulated by enzymes.

都受酶調節。

The life-sustaining power of enzymes lies in the fact

酶的維持生命力在於事實

that they catalyze reactions in

他們催化反應

mild conditions of pH, temperature,

溫和的pH值，溫度，

and atmospheric pressure.

和大氣壓力。

The rates of catalyzed reactions are millions to

催化反應的速率是數百萬到

trillions times faster than those of the

比那些快幾萬億倍

same reactions uncatalyzed.

相同的反應未催化。

To speed up a reaction in the absence of enzymes,

為了在沒有酶的情況下加速反應，

additional energy would need to be

需要額外的能量

provided as heat, which is jostles the

作為熱量提供，這是爭奪

substrates and occasionally provides

基板並偶爾提供

enough energy to trigger a reaction.

足夠的能量來引發反應。

In the course of most reactions,

在大多數反應過程中，

an unstable and highly energetic

不穩定，精力充沛

transition state is formed as the

過渡狀態形成為

substrates are transformed into products.

基板轉化為產品。

An enzyme acts as a template for

酶充當模板

the reaction, binding to its substrate and

反應，與其底物結合

holding it in the proper position to

把它放在適當的位置

form the product. An enzyme also

形成產品。一種酶也

surrounds the substrate with reactive groups

用反應基團包圍基底

that stabilize the transition state, making

這樣可以穩定過渡狀態

it easier for the reaction to occur.

反應更容易發生。

To understand how enzymes work, let's take a

為了理解酶的工作原理，讓我們來看看

closer look at a reaction in the

仔細看看中的一個反應

Citric Acid Cycle that is catalyzed by the

由檸檬酸催化的檸檬酸循環

enzyme aconitase. Aconitase binds to

酶烏頭酸酶。烏頭酶結合

its substrate citrate and removes a

它的基質檸檬酸鹽並去除a

hydroxyl group and a hydrogen atom to

羥基和氫原子

form intermediate cis-aconitate.

形成中間順式 - 順式。

It then adds the hydrogen in the hydroxyl back

然後它在羥基中加入氫

in slightly different positions to form

形成略有不同的立場

the product isocitrate.

產品是異檸檬酸。

In the active site, some amino acids are

在活性部位，有些氨基酸是

perfectly positioned to recognize the

完全定位以識別

substrate and hold it in the optimal

基板並將其保持在最佳狀態

position for the reaction to begin.

反應開始的位置。

Some amino acids are involved in

一些氨基酸參與

recognizing and holding the substrate.

識別並保持基板。

Other amino acids are directly involved in catalysis.

其他氨基酸直接參與催化。

00:02:41,040 --> 00:02:43,140 Histidine 101 acts as an acid by donating its proton.

00:02:41,040 --> 00:02:43,140 組氨酸101通過捐贈質子作為酸。

Thanks to the chemical environment of Serine 642,

感謝Serine 642的化學環境，

it can act as a base by accepting the

它可以通過接受它作為基礎

proton from the substrate.

來自基質的質子。

The active site of aconitase also contains

烏頭酸酶的活性部位也含有

an iron-sulfur cluster that stabilizes the

一個穩定鐵的硫鐵簇

substrate electrostatically and helps to

基板靜電並有助於

position it relative to the catalytic residues.

將其相對於催化殘留物定位。

The first step in the reaction is dehydration.

反應的第一步是脫水。

In this step, histidine acts as an acid

在這一步中，組氨酸起酸的作用

and protonates the hydroxyl

並使羥基質子化

on the substrate allowing it to

在基板上允許它

leave as a water molecule.

離開作為水分子。

Serine then acts as a base by extracting

然後絲氨酸通過提取作為基礎

a hydrogen atom from the opposite side

來自對面的氫原子

of the substrate forming the intermediate cis-aconitate.

形成中間順式烏頭酸酯的底物。

Cis-aconitate then flips

Cis-aconitate然後翻轉

upside down, and the complementary

顛倒，互補

hydration reaction is performed.

進行水合反應。

In this step, histidine grabs a hydrogen atom

在該步驟中，組氨酸捕獲氫原子

from a passing water molecule,

從一個通過的水分子，

placing the resulting hydroxyl group

放置所得的羥基

back onto the substrate. Serine then returns its

回到基板上。絲氨酸然後返回它

hydrogen atom and the final product

氫原子和最終產物

isocitrate is released.

isocitrate被釋放。

Notice that the enzyme itself was not changed by the reaction.

注意，酶本身沒有被反應改變。

It extracted the hydroxyl group

它提取了羥基

and a hydrogen atom and then put them back,

和一個氫原子，然後把它們放回去，

starting and ending in the same state.

以相同的狀態開始和結束。

This is the hallmark of a catalyst,

這是催化劑的標誌，

when it finishes a reaction, it is ready

當它完成反應時，就準備好了

for the next, so it can perform thousands

對於下一個，所以它可以執行數千

of reactions in a row.

連續的反應。

Notice also that the shape of an active site is often flexible.

另請注意，活動站點的形狀通常是靈活的。

Many enzymes surround their

許多酶圍繞著它們

substrates, closing around them to form

基板，圍繞它們形成

the perfect environment for a reaction.

完美的反應環境。

Enzymes are fundamental to life on Earth,

酶是地球上生命的基礎，

working every second of every day to

每天工作到每天

maintain life processes in every cell,

保持每個細胞的生命過程，

and in every living creature on the planet.

在這個星球上的每一個生物中。