托福听力词汇以及相关背景知识的积累，是一个相当漫长的过程，需要考生在平时的生活中多总结，多记忆。小编为大家整理了托福听力生物学背景知识：端粒，希望对各位同学的托福听力备考有所帮助：

Introduction：

Telomere

端粒(Telomere)是真核生物染色体末端的一种特殊结构,实质上是一重复序列,作用是保持染色体的完整性。细胞分裂一次,由于 DNA 复制时的方向必须从 5'方向到 3'方向,DNA 每次复制端粒就缩短一点,所以端粒其长度反映细胞复制史及复制潜能,被称作细胞寿命的“有丝分裂钟”。当细胞分裂一次,每条染色体的端粒就会逐次变短一些,构成端粒的一部分基因约 50~200 个核苷酸会因多次细胞分裂而不能达到完全复制(丢失),以至细胞终止其功能不再分裂。因此,严重缩短的端粒是细胞老化的信号。在某些需要无限复制循环的细胞中,端粒的长度在每次细胞分裂后被能合成端粒的特殊性 DNA 聚合酶-端粒酶所保留。

Background information：

A chromosome is packaged and organizedchromatin, a complex of macromolecules found in cells, consisting of DNA,protein and RNA. The main information-carrying macromolecule is a single pieceof coiled double-stranded DNA, containing many genes, regulatory

elements and other non-coding DNA. TheDNA-bound macromolecules are proteins, which serve to package the DNA andcontrol its functions. Chromosomes vary widely between different organisms.Some species also contain plasmids or other extra chromosomal DNA.

A telomere is a region of repetitivenucleotide sequences at each end of a chromatid, which protects the end of thechromosome from deterioration or from fusion with neighbouring chromosomes.

During chromo some replication, the enzymesthat duplicate DNA cannot continue their duplication all the way to the end ofa chromosome, so in each duplication the end of the chromosome is shortened(this is because the synthesis of Okazaki fragments requires RNA primersattaching ahead on the lagging strand). The telomeres are disposable buffers atthe ends of chromo somes which are truncated during cell division; theirpresence protects the genes before them on the chromosome from being truncatedinstead.

Over time, due to each cell division, the telomereends become shorter.They are replenished by an enzyme, telomerase reversetranase.

Knowledge points：

1. 染色体是成套的,有组织的染色质,在细胞中的复杂的子,由 DNA,蛋白质, RNA组成。

2. 端粒是在染色体末端的重复的核苷酸序列。它保护染色体的末端和它周围的染色体变坏或者融化。

3. 染色体复制的过程中,复制 DNA 的生化酶不能够继续复制,因此每经过一次复制, 染色体的末端就会变短。端粒是在染色体末端可供使用的缓冲器,每次细胞分裂就会变短。端粒保护基因被截断。

Vocabulary prediction：

Chromosome 染色体

Telomere 端粒

Telomerase 端粒酶

Sequence 序列

Test Point – TPO12L1

The assumption is that even these DNAdoesn’t make up any of the genes it must serve some other purpose. Anyway, ifwe examine these ends of these coils of DNA, we will find a sequence of DNA ateach end of every human Chromosome, called a telomere. Now a telomere is ahighly repetitious and genetically meaningless sequence of DNA, what we werecalling JUNK DNA. But it does have any important purpose; it is sort of likethe plastic tip on each end of shoelace. It means not help you tie your shoebut that little plastic tip keeps the rest of the shoelace, the shoe stringfrom unraveling into weak and useless threads. Well, the telomere at the end ofChromosomes seems to do about the same thing--- protect the genes thegenetically functional parts of the Chromosome from being damaged. Every timethe Chromosome divides, every time one cell divides into two. Pieces of theends of the Chromosome, the telomere, get broken off. So after each division,the telomere gets shorter and one of the things that may happen after a whileis that pieces of the genes themselves get broken off the Chromosomes. So theChromosome is now losing important genetically information and is no longerfunctional. But as long as the telomeres are at certain length they keep thisfrom happening. So it seems that, when the, by looking at the length of thetelomeres on specific Chromosomes we can actually predict pretty much how longcertain cells can successfully go on dividing. Other some cells just seem tokeep on dividing regardless which mean not be always a good thing if it getsout of control.

Knowledge points

1.如果我们检查 DNA 的末端,我们会在每个染色体的末端发现一个 DNA 序列。

2.端粒(在染色体端位上的着丝点)是一个高度重复的和无意义遗传的 DNA 序列。我们叫做 JUNK DNA. 但是它确实有重要的功能,它就像是鞋带前面的塑料头。它的作用不是系鞋子,但是这个小的塑料头维持整根鞋带,没有它鞋带就变成了无用的线。

3.端粒的作用和塑料头一样,保护染色体上遗传因子。每次染色体分裂的时候,一个细胞会分成两个。染色体末端的碎片,端粒,也会破裂。因此每次分裂之后,端粒会变短,并且遗传因子的碎片也会从染色体上剥离。因此染色体会失去它重要的遗传作用。但是只有端粒有一定的长度,就不会有这种情况发生。因此通过观察特定染色体上端粒的长度,我们可以预测某些细胞可以分裂多长。其他细胞一直分裂下去,并不是一件好事,因为会失去控制。