Name: 【TED-Ed】當你的DNA受損時會發生什麼？- Monica Menesini (【TED-Ed】What happens when your DNA is damaged? - Monica Menesini)
Uploaded: 2021-01-14T05:47:33.000Z
Duration: 4 min 59 s

gets damaged tens of thousands  of times per day.

Multiply that by your body's hundred trillion or so cells,

and you've got a quintillion  DNA errors everyday.

也就是說一天內你會有一百萬的三次方處分子損壞。

And because DNA provides the blueprint for the proteins  your cells need to function,

而正因DNA提供了你細胞所需要製造的蛋白質的藍圖，

damage causes serious problems, such as cancer.

這些損壞會帶來嚴重後果，比如：癌症。

Sometimes nucleotides,  DNA's building blocks, get damaged,

有時是核苷酸(組成DNA的基本單元)受損，

other times nucleotides get matched up incorrectly,causing mutations,

有時是核苷酸的配對錯誤導致的衰變，

and nicks in one or both strands can interfere with DNA replication,

而不論是單邊或雙邊的缺口都可能影響DNA的複製，

or even cause sections of DNA to get mixed up.

Fortunately, your cells have ways of fixing most of these problems most of the time.

但別擔心，通常，你的細胞都有辦法解決大部分的問題。

These repair pathways  all rely on specialized enzymes.

這些修復途徑都需依賴特殊的酵素。

Different ones respond  to different types of damage.

不同的酵素負責解決不同的損壞問題。

最常見的一種損壞就是鹼基錯配。

每個核苷酸分子都含有一個鹼基，

the enzyme DNA polymerase is supposed to bring in the right partner

to pair with every base on each template strand.

Adenine with thymine, and guanine with cytosine.

腺嘌呤配胸腺嘧啶，鳥嘌呤配胞嘧啶。

But about once every hundred thousand additions,

The enzyme catches  most of these right away,

and cuts off a few nucleotides and replaces them with the correct ones.

並將一些核苷酸去除並換上正確的。

a second set of proteins  comes behind it to check.

they cut out the incorrect nucleotide and replace it.

便將錯誤的核苷酸去除並換上正確的。

Together, these two systems reduce the number of base mismatch errors to about one in one billion.

在兩組系統的合作下，鹼基錯配的數量，每一億個裡會大約下降至一個。

But DNA can get damaged after replication, too.

Lots of different molecules can cause chemical changes to nucleotides.

許多不同的分子都會造成核苷酸的化學變化。

Some of these come  from environmental exposure,

比如某些菸草內含有的化合物。

But others are molecules that are found in cells naturally,like hydrogen peroxide.

但其他原因都是自然來自於細胞內的物質，比如過氧化氫。

Certain chemical changes are so common that they have specific enzymes assigned to reverse the damage.

有些化學變化非常普遍，因此有特定酵素被指派去修復它們的損壞。

But the cell also has more general repair pathways.

但細胞還有更多不同的修復途徑。

it can usually be fixed by a process called base excision repair.

通常可以由稱為「鹼基切除修復」的程序修復。

and other enzymes come in to trim around the site and replace the nucleotides.

其他酵素則在該處進行修剪，並換上正確得核苷酸。

UV light can cause damage  that's a little harder to fix.

紫外線造成的損壞，修復起來比較困難一點。

Sometimes, it causes two adjacent nucleotides to stick together,

有時，它會造成兩個鄰近的核苷酸黏在一起，

Damage like this requires  a more complex process

如此的損壞需要更複雜的修復過程，

A team of proteins removes a long strand of 24 or so nucleotides,

一組蛋白質會將含有約24個核苷酸的其中一長股去除，

Very high frequency radiation, like gamma rays and x-rays,

諸如gamma射線或X射線這類高頻率的射線，

They can actually sever one or both strands of the DNA backbone.

他們可能會切斷一股甚至雙股的DNA主幹。

Double strand breaks are the most dangerous.

就算只有一處也可能造成細胞死亡。

The two most common pathways for repairing double strand breaks

兩種最常見修復雙股斷裂的途徑

are called homologous recombination and non-homologous end joining.

稱為「同源性重組」和「同源性末端接合」。

Homologous recombination uses an undamaged section of similar DNA as a template.

「同源性重組」利用一段相似，而且未受損的DNA為範本。

Enzymes interlace the damaged and undamgaed strands,

酵素促使受損與未受損的兩股相互交織，

get them to exchange sequences of nucleotides,

並且使它們得以交換核苷酸的排序，

to end up with two complete double-stranded segments.

最終產生兩段完整的雙股區段。

Non-homologous end joining, on the other hand, doesn't rely on a template.

相反地，「同源性末端接合」，不需要依賴任何範本。

Instead, a series of proteins trims off a few nucleotides

而是一系列的蛋白質取出某些核苷酸，

and then fuses the broken ends  back together.

It can cause genes to get mixed up, or moved around.

But it's useful when sister DNA isn't available.

但缺乏一組相似的DNA時，也是很有用的。

Of course, changes to DNA  aren't always bad.

當然，DNA的轉換也不全是負面的。

Beneficial mutations  can allow a species to evolve.

But most of the time,  we want DNA to stay the same.

但大多數時候，我們希望DNA保持原貌。

Defects in DNA repair are associated with premature aging and many kinds of cancer.

DNA修復的疏失與早性老化和數種癌症有關。

So if you're looking for  a fountain of youth,

其實它早已存在你細胞的運作中，

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【TED-Ed】當你的DNA受損時會發生什麼？- Monica Menesini (【TED-Ed】What happens when your DNA is damaged? - Monica Menesini)

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