『新东方在线托福听力』为托福考生准备了ETS托福TPO/Official 12 Lec 1听力练习：What does the professor mainly discuss?原文题目答案解析，TPO/Official 12 Lec 1听力原文范文音频翻译。

托福TPO/Official 12 Lec 1听力原文What does the professor mainly discuss?【新东方在线】

旁白：听一段关于生物的讲座。

Narrator: Listen to part of a lecture in a Biology Class.

教授：我们学了人类细胞内的DNA如何控制细胞的生长和发展，那么就可以解释一个非常重要的观察研究了，这个观察表明当我们想要在实验室培育大多数的人类细胞时，它们像被设计好的一样在活性失去之前只分裂那么几次。

Professor: As we learn more about the DNA in human cells and how it controls the growth and development of cells, then maybe we can explain a very important observation, that when we try to grow most human cells in a laboratory, they seem programmed to divide only a certain number of times before they die.

在这里，不同的细胞是不同的。

一些细胞，比如神经细胞，只在有活性的过程中分裂七到九次。

Some cells, like nerve cells, only divide seven to nine times in their total life.

其它的，比如皮肤细胞，分裂的次数大大高于它。

Others, like skin cells, will divide many, many more times.

但最终，细胞们都会停止更新，然后失去活性。

But finally the cells stop renewing themselves and they die.

而且在人类体内的细胞中，在所有器官、几乎每种身体组织中，这样的事也终究会发生。

And in the cells of the human body itself, in the cells of every organ, of almost every type of tissue in the body, the same thing will happen eventually.

好，你们知道，所有人的遗传基因都存在于一个非常长的，叫做染色体的DNA中，人类每个细胞中共有46条DNA。

OK, you know that all of persons' genetic information is contained on very long pieces of DNA called Chromosomes, 46 of them in the human cells.

也就是23对染色体，在人体细胞中，每个有特定的长度和大小。

That's 23 pairs of these Chromosomes of various length and sizes.

如果你粗略看一下一张它的图片，一个染色体正在分裂成两个。

Now if you look at this rough drawing of one of them, one Chromosome about to divide into two.

它的样子有点让我们联想到，当然它比看上去要复杂的多，它看上去像一些弹簧连在一起，盘卷成了DNA。

You'll see that it sort of looks like, well actually, it's much more complex than this, but it reminds us of a couple of springs linked together to coiled up pieces of DNA.

当你把它们展开，你会发现它们涵盖了一些基因，一些决定身体细胞如何生长的DNA序列。

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.

当学者仔细看DNA中的染色体，他们都惊叹了，我们都很惊叹，因为仅仅一个大概20-30%的片段，就可以转化成涵义丰富的基因信息。

When researchers looked 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.

但如果你取走所有为基因编码的DNA，还会剩下大概70%的DNA。

But if you took away all the DNA that codes for genes, you still have maybe 70% of the DNA left over.

尽管垃圾这个词用起来有点半开玩笑的意思。

Though the word junk is used sort of tongue in cheek.

我们假设即使这些DNA不能产生基因，它肯定有点其它什么用途。

The assumption is that even if these DNA doesn't make up any of the genes, it must serve some other purpose.

不论如何，当我们检查这些盘卷的DNA的尾部，我们发现每个人类染色体的尾部都有一个特定的DNA序列，它叫做端区。

Anyway, if we examine this ends of these coils of DNA, we will find a sequence of DNA at each end of every human Chromosome, called a telomere.

端区是一个高度重复，没有遗传意义的DNA序列，也就是我们说的垃圾DNA。

Now a telomere is a highly repetitious and genetically meaningless sequence of DNA, what we were calling JUNK DNA.

但是它的确有一个重要的目的，它有点像鞋带两头的塑料头。

But it does have an important purpose: it is sort of like the plastic tip on each end of shoelace.

它可能不会帮助你系上鞋带，但这两个塑料头帮助鞋带的其它部分，线绳的部分，不至于脱线，变成脆弱没用的线头。

It may 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.

染色体两头的端区（也叫端粒）看上去做的是同样的事，来保护基因，那些有基因功能的染色体部分不至于被毁坏。

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.

每次染色体分裂，一个分裂成两个，染色体的尾部，也就是端区，就会发生断裂。

Every time the Chromosome divides, every time one cell divides into two, pieces of the ends of the Chromosome, the telomeres, get broken off.

所以每经过一次分裂，端区就会变得更短，一段时间后，有可能发生的是，一些基因从染色体中被破除掉了。

So after each division, the telomeres get shorter and one of the things that may happen after a while is that pieces of the genes themselves get broken off the Chromosomes.

这样染色体就失去了重要的基因信息，导致它失去了它的功能。

So the Chromosome is now losing important genetic information and is no longer functional.

但只要端区维持着一定的长度，它们保证这种事不会发生。

But as long as the telomeres are at certain length, they keep this from happening.

所以这看上去……通过观察一些特定的染色体的端区，我们可以预测多长的染色体可以成功分裂。

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.

有一些染色体不论如何都会进行分裂，这并不是一件好事，因为它有可能（由于过度分裂）而失去控制。

Now, there are some cells that just seem to keep on dividing regardless, which may not be always a good thing if it gets out of control.

但当我们用化学方法分析这些细胞，我们发现了一个很有趣的事，一个化学物质，一种叫做端粒酶的酶。

But when we analyze the cells chemically, we find something very interesting, a chemical in them, and an enzyme called telomerase.

当端粒从染色体中断裂开，这种化学物质，这个端粒酶可以重建它，可以重新组装这个具有保护功能的DNA，也就是染色体失去的端粒。

As bits of the telomere break off from the end of Chromosome, this chemical, this telomerase can rebuild it, can help reassemble the protective DNA, the telomere that the Chromosome is lost.

有一天，借助端粒酶，我们或许能够取出任何一种细胞，使其永久性地拥有活性和复制自己。

Someday we may be able to take any cell and keep it alive functioning and reproducing itself essentially forever through the use of telomerase.

在将来，我们可能有真正意义上的长生不老的神经细胞、皮肤细胞等等，因为端粒酶可以构建端粒，使得染色体不会变得更短。

And in the future, we may have virtually immortal nerve cells and immortal skin cells of whatever because these chemical, telomeres can keep the telomere on the ends of Chromosomes from getting any shorter.

The professor discusses research about the percentage of a chromosome’s DNA that contains genetic information. How did she feel about this research?

What does the professor say about the DNA in a telomere?

Why does the professor mention shoelaces?

What does the professor imply about the length of the telomeres on a cell's chromosomes?

According to the professor, how is the chemical telomerase related to the telomere?

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