You can think of your cells as the kitchen in a busy restaurant.
你可以把你的细胞想象成繁忙的餐馆厨房。
Sometimes your body orders chicken. Other times, it orders steak.
有时候你的身体想点一份鸡肉。有时候它又会想点一份牛排。
Your cells have to be able to crank out whatever the body needs and quickly.
你的细胞得有能力制造出身体需要的一切，而且要快。
When an order comes in, the chef looks to the cookbook, your DNA, for the recipe.
当点单出现后，主厨开始翻阅菜谱，你的DNA，来查找配方。
She then transcribes that message onto a piece of paper called RNA and brings it back to her countertop, the ribosome.
她然后将这个信息抄录到一张叫做RNA的纸上，并将RNA带到她的工作台上--核糖体。
There, she can translate the recipe into a meal, or for your cells, a protein,
在那里，她可以用菜谱做成美味的一道菜，对细胞来说就是一种蛋白质，
by following the directions that she's copied down.
这一切只要按照抄录的菜谱就可以了。
But RNA does more for the cell than just act as a messenger between a cook and her cookbook.
但细胞中的RNA不仅仅是厨师和他的笔记之间的一个信号传递者。
It can move in reverse and create DNA,
它可以反向生成DNA，
it can direct amino acids to their targets, or it can take part in RNA interference, or RNAi.
它可以指导氨基酸到达其它目标位置，它也可以在RNA干扰，也就是RNAi中发挥作用。
But wait! Why would RNA want to interfere with itself?
等等！为什么RNA想干扰它自己呢？
Well, sometimes a cell doesn't want to turn all of the messenger RNA it creates into protein,
有时候细胞并不想将所有的信使RNA都翻译成蛋白质；
or it may need to destroy RNA injected into the cell by an attacking virus.
有时候它需要把被病毒入侵的细胞的RNA消灭掉来摧毁掉病毒。
Say, for example, in our cellular kitchen, that someone wanted to cancel their order or decided they wanted chips instead of fries.
比如，在我们的细胞厨房中，有人想取消订单，或者决定用炸薯条替代油炸小鱼。
That's where RNAi comes in.
这时候RNAi就发挥作用了。
Thankfully, your cells have the perfect knives for just this kind of job.
幸好你的细胞有合适的刀具能胜任这样的工作。
When the cell finds or produces long, double-stranded RNA molecules,
当细胞发现或产生了长双链RNA分子，
it chops these molecules up with a protein actually named dicer.
它将这些分子用称作切酶的蛋白质切成小段。
Now, these short snippets of RNA are floating around in the cell,
现在这些小段RNA在细胞中漂浮着，
and they're picked up by something called RISC, the RNA Silencing Complex.
并被称作“RNA诱导沉默复合体”（简称RISC）发现。
It's composed of a few different proteins, the most important being slicer.
它由几个不同的蛋白组成，最重要的就是切酶。

This is another aptly named protein, and we'll get to why in just a second.
这个蛋白的名字也很合适，我们很快就会知道为什么。
RISC strips these small chunks of double-stranded RNA in half,
RISC把这些小块的双链RNA拆成两份，
using the single strand to target matching mRNA, looking for pieces that fit together like two halves of a sandwich.
用单链来匹配目标mRNA，寻找着合适的另一半，就像三明治的两半。
When it finds the matching piece of mRNA, RISC's slicer protein slices it up.
当它找到匹配的mRNA，RISC的切割蛋白把它切掉。
The cell then realizes there are odd, strangely sized pieces of RNA floating around and destroys them,
然后细胞会发现这些奇特古怪的RNA片段四处飘荡，
preventing the mRNA from being turned into protein.
然后摧毁它们以阻止mRNA翻译成蛋白质。
So, you have double-stranded RNA, you dice it up, it targets mRNA, and then that gets sliced up, too.
所以当以有双链RNA时，你会把它切开，它匹配mRNA，然后那一段也会被切掉。
Voila! You've prevented expression and saved yourself some unhappy diners.
瞧！你阻止了错误的表达，避免自己吃一顿难吃的饭。
So, how did anybody ever figure this out?
那么这个是怎么被发现的呢？
Well, the process was first discovered in petunias
这个过程首先被发现在南美矮牵牛花中，
when botanists trying to create deep purple blooms introduced a pigment-producing gene into the flowers.
当植物学家试着创造深紫色花朵时，他们引入了一段色素基因进入细胞。
But instead of darker flowers, they found flowers with white patches and no pigment at all.
但他们没看到颜色更深的花朵，却只看到了白色，全然没有色素出现。
Instead of using the RNA produced by the new gene to create more pigment,
花朵并没有使用新基因产生的RNA来生成色素，
the flowers were actually using it to knock down the pigment-producing pathway,
实际上这些花在用产生的RNA来敲除色素生成通路，
destroying RNA from the plant's original genes with RNAi, and leaving them with pigment-free white flowers.
用RNAi摧毁了来自植物自己基因的RNA，最终这些花都是无色素的白花。
Scientists saw a similar phenomena in tiny worms called C. elegans,
科学家还在一种小型蠕虫--线虫的体内发现了类似的情况，
and once they figured out what was happening, they realized they could use RNAi to their advantage.
当他们弄明白发生了什么以后，他们意识到可以用RNAi来帮助他们。
Want to see what happens when a certain gene is knocked out of a worm or a fly?
想看看特定基因被敲除以后的蠕虫或者苍蝇长什么样吗？
Introduce an RNAi construct for that gene, and bam! No more protein expression.
构建一段针对相关基因的RNAi，砰！再也不会表达相关蛋白了。
You can even get creative and target that effect to certain systems,
再创造性一点，你可以针对特定系统敲除基因，
knocking down genes in just the brain, or just the liver, or just the heart.
可以在大脑中，在肝脏中或者在心脏中。
Figuring out what happens when you knock down a gene in a certain system can be an important step in figuring out what that gene does.
弄清敲除某个系统的特定基因的效应，是了解这段基因功能的重要的一步。
But RNAi isn't just for understanding how things happen.
然而RNAi不仅可用来理解事情的发生。
It can also be a powerful, therapeutic tool and could be a way for us to manipulate what is happening within own cells.
它也可以成为一个强大的治疗工具，也可以成为我们控制细胞内部的一种方法。
Researchers have been experimenting with using it to their advantage in medicine,
研究者们已经开始试着用它来改进药物，
including targeting RNA and tumor cells in the hopes of turning off cancer-causing genes.
包括瞄准特定RNA和肿瘤细胞，希望能关闭致癌基因。
In theory, our cellular kitchens could serve up an order of cells, hold the cancer.
理论上，我们的细胞厨房可以处理细胞的订单，并阻止癌症。