Part I
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.
Now this differs with the type of cell. Some cells, like nerve cells, only divide seven to nine times in their total life. Others, like skin cells, will divide many, many more times. But finally the cells stop renewing themselves and they die. 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.
随着我们越来越多地了解人类细胞中的DNA以及它是如何控制细胞的生长和发育的，我们或许就可以解释一个非常重要的观察结果，即当我们尝试在实验室中培养人类的大多数细胞时，那些细胞在死亡之前，似乎注定只能分裂一定的次数。
1. DNA
DNA is an acid in the chromosomes in the centre of the cells of living things. DNA determines the particular structure and functions of every cell and is responsible for characteristics being passed on from parents to their children. DNA is an abbreviation for (缩略=) 'deoxyribonucleic acid'. 脱氧核糖核酸（动植物的细胞中带有基因信息的化学物质）
2. cell |sel|
noun. the smallest unit of living matter that can exist on its own. All plants and animals are made up of cells 细胞
E.g.: Those cells divide and give many other different types of cells.
那些细胞分裂，产生出许多不同种类的细胞。
3. programme|ˈprəʊgræm|
verb. if a living creature is programmed to behave in a particular way, they are likely to behave in that way because of social or biological factors that they cannot control 按特定的方式行事
E.g.: We are all genetically programmed to develop certain illnesses.
基因决定了我们都会患上某些疾病。
4. renew|rɪˈnju:|
verb. you can say that something is renewed when it grows again or is replaced after it has been destroyed or lost 使（受到损毁或丢失后)重获新生
E.g.:Cells are being constantly renewed.
细胞不断再生。
5. organ|ˈɔ:rgən|
noun. a part of the body that has a particular purpose, such as the heart or the brain; part of a plant with a particular purpose （人体或动植物的）器官
E.g.: the sexual/reproductive organs
性 / 生殖器官
6. tissue |ˈtɪsju:|
noun. a collection of cells that form the different parts of humans, animals and plants （人、动植物细胞的）组织
E.g.: As we age we lose muscle tissue.
肌肉组织会随着我们日趋衰老而萎缩。
Part II
OK, you know that all of persons' genetic information is contained on very long pieces of DNA called Chromosomes, 46 of them in a human cell, that's 23 pairs of these Chromosomes of various length and sizes. Now if you look at this rough drawing of one of them, one Chromosome's about to divide into two. 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 coil up pieces of 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. 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.
如果你把它们拉开拉直，你会发现它们含有某些基因，某些DNA序列，是用来决定人体细胞将如何发育的。
1. chromosome |ˈkroʊməsoʊm|
noun. one of the very small structures like threads in the nuclei (= central parts) of animal and plant cells, that carry the genes 染色体
E.g.: Each cell of our bodies contains 46 chromosomes.
我们人体的每个细胞都包含46个染色体。
2. spring |sprɪŋ|
noun. a twisted piece of metal that can be pushed, pressed or pulled but which always returns to its original shape or position afterwards 弹簧；发条
E.g.: Unfortunately, as a standard mattress wears, the springs soften and so do not support your spine.
遗憾的是，当一张标准床垫用旧后，弹簧就会变软而无法支撑你的脊椎。
3. coil |kɔɪl|
verb. to wind into a series of circles; to make sth do this （使）缠绕，盘绕
E.g.: The snake coiled up, ready to strike.
那条蛇盘绕起来准备攻击。
4. stretch|kɔɪl|
verb. to pull sth so that it is smooth and tight 拉紧；拉直；绷紧
E.g.: Stretch the fabric tightly over the frame.
把布在架子上绷紧。
5. sequence |ˈsi:kwəns|
noun. the order that events, actions, etc. happen in or should happen in 顺序；次序
E.g.: The tasks had to be performed in a particular sequence.
这些任务必须按一定次序去执行。
6. fraction |ˈfrækʃn|
noun. a small part or amount of sth 小部分；少量；一点儿
E.g.: Only a small fraction of a bank's total deposits will be withdrawn at any one time.
任何时候，一家银行的总存款只有少量会被提取。
7. convert |kənˈvɜ:t|
verb. if one thing is converted or converts into another, it is changed into a different form (使)改变;更改;(使)转变
E.g.: The signal will be converted into digital code.
信号会被转变为数字代码。
Part III
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. Though the word "junk" is used sort of tongue-in-cheek. The assumption is that even if these DNA doesn't make up any of the genes, it must serve some other purpose. 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.
Now a telomere is a highly repetitious and genetically meaningless sequence of DNA, what we were calling JUNK DNA. But it does have an important purpose: it is sort of like the plastic tip on each end of shoelace. 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.
那个假设就是，即使这些DNA不构成任何基因，它也很可能有其它的作用和目的。
1. code|koʊd|
verb. to code something means to give it a code or to mark it with its code 把…编码(或编号)
E.g.: He devised a way of coding every statement uniquely.
他设计了一种把每句话进行独特编码的方法。
2. tongue-in-cheek
adj. not intended seriously; done or said as a joke 言不由衷的；随便说说的；开玩笑的
E.g.: Don't take her so seriously, that was just a tongue-in-cheek remark.
不要对此太认真, 她只是半开玩笑地说这话的。
3. telomere |'teləˌmɪr|
noun. telomeres act as caps to keep the sticky ends of chromosomes from randomly clumping together 端粒是真核生物染色体末端的DNA重复序列，作用是保持染色体的完整性和控制细胞分裂周期。由于DNA复制的机制，每次染色体复制后，延迟股上的染色体末端必无法被复制。因此，真核生物在染色体末端演化出端粒以作为可被重复遗弃的片段。一旦端粒消耗殆尽，细胞将会立即启动凋亡机制。因此，端粒被推测和细胞衰老有明显的关系）。
4.repetitious |ˌrepəˈtɪʃəs|
adj. involving sth that is often repeated 重复的；一再的；反反复复的
E.g.: a long and repetitious speech
冗长重复的讲话
5. tip |tɪp|
noun. a small part that fits on or over the end of sth （装在顶端的）小部件
E.g.: a walking stick with a rubber tip
带橡皮头的手杖
6. shoelace |ˈʃu:leɪs|
noun. a long thin piece of material like string that goes through the holes on a shoe and is used to fasten it 鞋带
E.g.: Your shoelace is undone.
你的鞋带松开了。
7. unravel |ʌnˈrævl|
verb. if you unravel threads that are twisted, woven or knitted, or if they unravel , they become separated （把缠或织在一起的线）解开，拆散，松开
E.g.: I unravelled the string and wound it into a ball.
我把绳子解开并绕成一个球。
8. thread |θred|
noun. a thin string of cotton, wool, silk, etc. used for sewing or making cloth （棉、毛、丝等的）线
E.g.: the delicate threads of a spider's web
蜘蛛网的纤丝
Part IV
Well, the telomeres 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. Every time the Chromosome divides, every time one cell divides into two, pieces of the ends of the Chromosome, the telomeres, get broken off. 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.
So the Chromosome is now losing important genetic information and is no longer functional. But as long as the telomeres are at certain length, they keep this from happening. 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.
因此每次分裂之后，端粒都会变短，而且一段时间之后基因片段本身也可能会从染色体上脱落。
1. functional|ˈfʌŋkʃənl|
adj. functional equipment works or operates in the way that it is supposed to 在工作的;在起作用的;运转正常的
E.g.: We have fully functional smoke alarms on all staircases
我们在各层楼梯都安装有完全可用的烟雾警报器。
2. break off
to become separated from sth as a result of force 断开；折断
E.g.: The back section of the plane had broken off.
飞机尾部脱落了。
3. division |dɪˈvɪʒn|
noun. the process or result of dividing into separate parts; the process or result of dividing sth or sharing it out 分开；分隔；分配；（分出来的）部分
E.g.: cell division
细胞分裂
Part V
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. But when we analyze the cells chemically, we find something very interesting, a chemical in them, and an enzyme called telomerase. 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 has lost.
Someday we may be able to take any cell and keep it alive, functioning and reproducing itself essentially forever through the use of telomerase. And in the future, we may have virtuallyimmortal nerve cells and immortal skin cells or whatever, because this chemical, telomerase can keep the telomeres on the ends of Chromosomes from getting any shorter.
在未来，我们可能会拥有几乎永生的神经细胞，永生的皮肤细胞等等，因为这种化学物质，端粒酶可以防止染色体末端的端粒变短。
1. regardless|rɪˈgɑ:dləs|
adv. paying no attention, even if the situation is bad or there are difficulties 不管怎样;无论如何;不顾一切地
E.g.: The weather was terrible but we carried on regardless.
天气非常恶劣，但我们并不理会，照常进行。
2. enzyme |ˈenzaɪm|
noun. a substance, produced by all living things, which helps a chemical change happen or happen more quickly, without being changed itself 酶
E.g.: This enzyme would make the filtration of beer easier.
这种酶会使啤酒更容易过滤。
3. reassemble |ˌri:əˈsembl|
verb. to fit the parts of sth together again after it has been taken apart 重组；重新整合；重新装配
E.g.: We will now try to reassemble pieces of the wreckage.
我们现在会尽量把残骸重新组合起来。
4. virtually |ˈvɜ:tʃuəli|
adv. almost or very nearly, so that any slight difference is not important 几乎；差不多；事实上；实际上
E.g.: Virtually all students will be exempt from the tax.
差不多所有的学生都可免此税项。
5. immortal |ɪˈmɔ:rtl|
adj. that lives or lasts for ever 不死的;长生的
E.g.: The pharaohs were considered gods and therefore immortal.
法老们被视为神灵，且长生不死。
