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Narrator:Listen to part of a lecture in a Biology Class.
獨白:聽下面一段生物課上的講座。
Professor:As we learn more about the DNA in human cells and how it controls the growth and development of cells,
教授:我們已經了解人類細胞內的 DNA 如何控制細胞的生長和發展，
then maybe we can explain a very important observation, that when we try to grow most human cells in laboratory,
那就可以解釋一個非常重要的觀察研究，這個觀察表明當我們想要在實驗室培育大多數的人類細胞時，
they seem programmed to divide only a certain number of times before they die.
它們像被設計好的一樣在活性失去之前只分裂那么幾次。
Now this differs with the type of cell.
在這里，不同的細胞是不同的。
Some cells, like nerve cells, only divide seven to nine times in their total life.
一些細胞，比如神經細胞，只在有活性的過程中分裂七到九次。
Others, like skin cells, will divide many, many more times.
其他的，比如皮膚細胞，分裂的次數要遠遠高于它
But finally the cells stop renewing themselves and they die.
但最終，細胞們都會停止更新，然后失去活性。
And in the cells of the human body itself, in the cells of every organ, of almost every type of tissues in the body, the same thing will happen eventually.
而且在人類體內的細胞中，在所有器官、幾乎每種身體組織中，這樣的事也終究會發生。
OK, you know that all of persons' genetic information is contained on very long pieces of DNA called Chromosomes.
好了，你們知道，所有人的遺傳基因都存在于一個非常長的，叫做染色體的 DNA 中。
46 of them are in the human cells that's23 pairs of these Chromosomes are of very lengths and sizes.
在人體細胞中的46條，也就是 23 對染色體，每條都有特定的長度和大小。
Now if you look at this rough drawing of one of them, one Chromosome is about to divide into two.
如果你粗略看一下一張它的圖片，一個染色體正在分裂成兩個。
You see that it sort of looks like, well actually it's much more complex than this but it reminds us a couple of springs linked together to coil up pieces of DNA.
它的樣子有點讓我們聯想到，當然它比看上去要復雜的多，它看上去像一些彈簧連在一起，盤卷成了 DNA。
And if you stretch them out you will find they contain certain genes, certain sequences of DNA that help to determine how the cells of the body will develop.
當你把它們展開，你會發現它們涵蓋了一些基因，一些決定身體細胞如何生長的 DNA 序列。
When researchers look really carefully at the DNA in Chromosomes though, they were amazed, we all were, to find that only a fraction of it, maybe 20-30%, converts into meaningful genetic information.
當學者仔細看 DNA 中的染色體，很令人驚訝，我們也很驚訝，因為僅僅一個大概20%-30%的片段，就可以轉化成涵義豐富的基因信息。
It's incredible; at least it was to me. But if you took away all the DNA that codes for genes, you still have maybe 70% of the DNA left over. That's the so-called JUNK DNA.
這非常神奇，至少對于我是。但如果你取走所有為基因編碼的 DNA，還會剩下大概 70%的 DNA，這就是所謂的“垃圾 DNA”，
Though the word junk is used sort of townies cheek.
盡管垃圾這個詞用起來有點半開玩笑的意思。
The assumption is that even these DNA doesn't make up any of the genes it must serve some other purpose.
我們假設即使這些 DNA 不能產生基因，它肯定有點其他什么用途。
Anyway, if we examine these ends of these coils of DNA, we will find a sequence of DNA at each end of every human Chromosome, called a telomere.
不論如何，當我們檢查這些盤卷的 DNA 的尾部，我們發現每個人類染色體的尾部都有一個叫做端區的特定DNA 序列。
Now a telomere is a highly repetitious and genetically meaningless sequence of DNA, what we were calling JUNK DNA.
端區是一個高度重復，沒有遺傳意義的 DNA 序列，也就是我們說的垃圾 DNA。
But it does have any important purpose; it is sort of like the plastic tip on each end of shoelace.
但是它的確有一個重要的目的，它有點像鞋帶兩頭的塑料頭。
It means not help you tie your shoe but that little plastic tip keeps the rest of the shoelace, the shoe string from unraveling into weak and useless threads.
它可能不會幫助你系上鞋帶，但這兩個塑料頭幫助鞋帶的其他部分，線繩的部分，不至于脫線，變成脆弱沒用的線頭。
Well, the telomere at the end of Chromosomes seems to do about the same thing-protect the genes the genetically functional parts of the Chromosome from being damaged.
染色體兩頭的端區看上去做的是同樣的事，來保護基因，那些有基因功能的染色體部分不至于被毀壞。
Every time the Chromosome divides, every time one cell divides into two.
每次染色體分裂，一個分裂成兩個，染色體的尾部，也就是端區，就會發生斷裂。
Pieces of the ends of the Chromosome, the telomere, get broken off.
所以每經過一次分裂，端區就會變得更短。
So after each division, the telomere gets shorter and one of the things that may happen after a while is that pieces of the genes themselves get broken off the Chromosomes.
一段時間后，有可能發生的是，一些基因從染色體中被破除掉了，
So the Chromosome is now losing important genetically information and is no longer functional.
這樣染色體就失去了重要的基因信息，導致它失去了它的功能。
But as long as the telomeres are at certain length they keep this from happening.
但只要端區維持著一定的長度，它們保證這種事不會發生。
So it seems that, when the, by looking at the length of the telomeres on specific Chromosomes we can actually predict pretty much how long certain cells can successfully go on dividing.
所以這看上去通過觀察一些特定的染色體的端區，我們可以預測多長的染色體可以成功分裂。
Other some cells just seem to keep on dividing regardless which mean not be always a good thing if it gets out of control.
有一些染色體不論如何都會進行分裂，這并不是一件好事，因為它有可能而失去控制。
But when we analyze the cells chemically we find something very interesting, a chemical in them, and an enzyme called telomerase.
但當我們用化學方法分析這些細胞，我們發現了一個很有趣的事實。
As bits of the telomere break off from the end of Chromosome, this chemical, this telomerase can rebuild it, can help resemble the protected DNA, the telomere that the Chromosome is lost.
一種化學物質，一種叫做端粒酶的酶。當端粒從染色體中斷裂開，這種化學物質，這個端粒酶可以重建它，可以重新組裝這個具有保護功能的 DNA，也就是染色體失去的端粒。
Someday we may be able to take any cell and keep it alive functioning and reproducing itself essentially forever through the use of telomerase.
有一天，借助端粒酶，我們或許能夠取出任何一種細胞，使其永久性地擁有活性和復制自己。
And in the future we may have virtually immortal nerve cells and immortal skin cells of whatever because of these chemical, telomerase can keep the telomere on the ends of Chromosomes from getting any shorter.
或許在不久的將來，我們可能有真正意義上的長生不老的神經細胞、皮膚細胞等等，因為端粒酶可以構建端粒，使得染色體不會變得更短。
