What happens when your DNA is damaged? - Monica Menesini

2,534,287 views ・ 2015-09-21

TED-Ed


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翻译人员: Deying Hu 校对人员: Gabriella Hu
00:06
The DNA in just one of your cells
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在你的一个细胞里的DNA
00:08
gets damaged tens of thousands of times per day.
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每天都受到上万次的破坏。
00:12
Multiply that by your body's hundred trillion or so cells,
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乘以你身体中数以百万亿的细胞,
00:16
and you've got a quintillion DNA errors everyday.
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每天你将得到百万的三次方的DNA错误。
00:21
And because DNA provides the blueprint
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并且因为DNA为你身体所需的蛋白质
00:23
for the proteins your cells need to function,
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提供蓝图,
00:26
damage causes serious problems, such as cancer.
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(DNA的)破坏会造成严重的后果,比如患上癌症。
00:30
The errors come in different forms.
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有很多种不同的错误。
00:32
Sometimes nucleotides, DNA's building blocks, get damaged,
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有的时候核苷酸,DNA的基础组成部分,受到了破坏;
00:37
other times nucleotides get matched up incorrectly,
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有时核苷酸配对错误,
00:41
causing mutations,
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造成了突变,
00:43
and nicks in one or both strands can interfere with DNA replication,
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一条或者两条DNA链中片段缺失会影响DNA链的折叠,
00:48
or even cause sections of DNA to get mixed up.
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甚至会引起DNA片段配对混乱
00:52
Fortunately, your cells have ways of fixing most of these problems
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幸运地是,你的细胞在绝大多数情况下
00:56
most of the time.
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有改正这些问题的能力。
00:58
These repair pathways all rely on specialized enzymes.
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这些修护的方法都依赖于特定的酶,
01:01
Different ones respond to different types of damage.
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不同的酶对应于不同种种的破坏。
01:05
One common error is base mismatches.
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一种常见的情况是碱基错配。
01:07
Each nucleotide contains a base,
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每一个核苷酸含有一个碱基,
01:10
and during DNA replication,
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在DNA复制阶段,
01:12
the enzyme DNA polymerase is supposed to bring in the right partner
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DNA聚合酶是用来确保正确的配对的,
01:16
to pair with every base on each template strand.
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以保证模板链上的碱基配对成功。
01:20
Adenine with thymine, and guanine with cytosine.
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腺嘌呤配胸腺嘧啶,鸟嘌呤配胞嘧啶。
01:24
But about once every hundred thousand additions,
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但是每增加十万次的配对,
01:27
it makes a mistake.
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就会产生一个错误。
01:28
The enzyme catches most of these right away,
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聚合酶能够及时找到大部分的错误,
01:31
and cuts off a few nucleotides and replaces them with the correct ones.
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并且减掉一小段核苷酸然后用正确的片段去替代。
01:35
And just in case it missed a few,
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为了以防万一它错漏了一些,
01:37
a second set of proteins comes behind it to check.
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又会有一组蛋白链返回检查。
01:41
If they find a mismatch,
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如果它们确实找到了错配的,
01:42
they cut out the incorrect nucleotide and replace it.
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它们会切断那段错误片段并用正确的片段替代他们,
01:46
This is called mismatch repair.
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这就是错配修复。
01:48
Together, these two systems reduce the number of base mismatch errors
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这两种检测系统将碱基错配的数目
01:52
to about one in one billion.
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减少到十亿分之一。
01:55
But DNA can get damaged after replication, too.
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但是DNA在复制之后也可能遭到破坏。
01:59
Lots of different molecules can cause chemical changes to nucleotides.
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很多不同的分子可能使核苷酸产生化学变化。
02:02
Some of these come from environmental exposure,
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一些变化是来自环境暴露,
02:06
like certain compounds in tobacco smoke.
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比如烟草烟雾中的特定化合物。
02:09
But others are molecules that are found in cells naturally,
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但是其他的是细胞中自带的分子,
02:12
like hydrogen peroxide.
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比如过氧化氢。
02:14
Certain chemical changes are so common
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某些化学变化实在是太常见了,
02:17
that they have specific enzymes assigned to reverse the damage.
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以至于它们有着特定的酶来扭转破坏。
02:21
But the cell also has more general repair pathways.
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但是细胞同样有普通的维护方式。
02:24
If just one base is damaged,
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如果只有一个碱基遭到了破坏,
02:27
it can usually be fixed by a process called base excision repair.
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它通常能够被一种称为碱基切除修复的方式维护。
02:32
One enzyme snips out the damaged base,
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一种酶剪掉受损的碱基,
02:34
and other enzymes come in to trim around the site and replace the nucleotides.
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其他的酶来修整破坏点并更换核苷酸。
02:40
UV light can cause damage that's a little harder to fix.
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紫外线造成的破坏会稍微难修复一点。
02:45
Sometimes, it causes two adjacent nucleotides to stick together,
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有时,它会造成两个相邻的核苷酸粘在一起,
02:49
distorting the DNA's double helix shape.
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使DNA双螺旋模型变形。
02:52
Damage like this requires a more complex process
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像这样的破坏需要更加复杂的修护过程,
02:55
called nucleotide excision repair.
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称为核苷酸切除修复。
02:58
A team of proteins removes a long strand of 24 or so nucleotides,
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一组蛋白质会去除一长串大约24个左右的核苷酸,
03:04
and replaces them with fresh ones.
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并且用新的核苷酸代替它们。
03:06
Very high frequency radiation, like gamma rays and x-rays,
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频率十分高的射线,比如伽马射线和X-射线,
03:10
cause a different kind of damage.
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引起另一种不同的破坏。
03:13
They can actually sever one or both strands of the DNA backbone.
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它们可以分离DNA骨架中的单链或双链。
03:18
Double strand breaks are the most dangerous.
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双链断裂是最危险的。
03:21
Even one can cause cell death.
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即使是单链断裂也可能引起细胞死亡。
03:24
The two most common pathways for repairing double strand breaks
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两种最常见的修复双链断裂破坏的方式,
03:27
are called homologous recombination and non-homologous end joining.
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被称为同源重组和非同源末端连接。
03:33
Homologous recombination uses an undamaged section of similar DNA as a template.
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同源重组利用一段未被破坏的相似DNA作为模板。
03:39
Enzymes interlace the damaged and undamgaed strands,
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酶使破坏链和未破坏链交错,
03:43
get them to exchange sequences of nucleotides,
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让他们交换核苷酸片段,
03:46
and finally fill in the missing gaps
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最终补充缺隙,
03:49
to end up with two complete double-stranded segments.
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得到两个完整的双链段。
03:53
Non-homologous end joining, on the other hand,
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另一方面,非同源末端连接,
03:55
doesn't rely on a template.
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不需要依赖于模板。
03:58
Instead, a series of proteins trims off a few nucleotides
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相反地,一系列的蛋白质剪切掉一些核苷酸,
04:02
and then fuses the broken ends back together.
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然后使断裂的端部融合在一起。
04:06
This process isn't as accurate.
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这个过程并不那么得精确。
04:08
It can cause genes to get mixed up, or moved around.
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它可能会造成基因错乱或者左右错动。
04:12
But it's useful when sister DNA isn't available.
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但是当姐妹染色体不可获取时它很有作用。
04:16
Of course, changes to DNA aren't always bad.
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当然,DNA的变化不总是有害的。
04:20
Beneficial mutations can allow a species to evolve.
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有益的突变能使种族进化。
04:23
But most of the time, we want DNA to stay the same.
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但是大多数情况下,我们希望DNA保持一致。
04:27
Defects in DNA repair are associated with premature aging
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DNA修复中的错误,
04:31
and many kinds of cancer.
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与过早衰老和许多种的癌症有关。
04:34
So if you're looking for a fountain of youth,
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所以如果你在寻找“青春之泉”,
04:36
it's already operating in your cells,
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它已经在你的细胞中了,
04:39
billions and billions of times a day.
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每日数十亿倍地不停运行着。
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