大学生物专业英语3

1、2022-4-61Lesson threeCellular reproduction: mitosis and meiosis2022-4-62objectivevUnderstand the concept of mitosis and meiosis.vControl the process of mitosis and meiosis.vDescripe the meaning of meiosis.2022-4-631. The nucleus and chromosomes2022-4-64vrepository n.贮藏室贮藏室, 智囊团智囊团, 知识库知识库, 仓库仓库vchro

2、mosome n.生物生物染色体染色体vhistone n.生化生化组蛋白组蛋白vnucleosome n.生化生化核小体核小体vchromatin n.核染质核染质, 染色质染色质vpictorial adj.图示的图示的 n.画报画报vkaryotype n.生物生物 染色体组型染色体组型vhomologous pair 同源染色体对同源染色体对vautosome n.正染色体正染色体, 常染色体常染色体vdiploid adj.双重的双重的, n.二倍体二倍体vhaploid n.生物生物单倍体单倍体 adj.单一的单一的2022-4-65vThe cell nucleus is the

3、 main repository of genetic information. v细胞核是贮藏遗传信息的主要场所。细胞核是贮藏遗传信息的主要场所。vWithin the nucleus are the chromosomestightly coiled strands of DNA and clusters of associated proteins.v细胞核里的是染色体紧密盘绕成螺旋的细胞核里的是染色体紧密盘绕成螺旋的DNA链和链和相关的成簇蛋白质。相关的成簇蛋白质。2022-4-66v Long stretches of the continuous DNA molecule wind

4、 around these clusters of proteins, or histones, forming beadlike complexes known as nucleosomes. v长链长链DNA分子缠绕着成簇的蛋白质，分子缠绕着成簇的蛋白质，或组蛋白，形成珠链状的核小体。或组蛋白，形成珠链状的核小体。2022-4-67nucleosome 核小体， 核粒The basic unit of chromatin structure in eukaryotic cells. A nucleosome consists of eight histone molecules of fo

5、ur different types, together with about 140 base pairs of DNA coiled around it.2022-4-68vMore coiling and supercoiling produces a dense chromosome structure. v进一步的螺旋和超螺旋形成致密的染色体组进一步的螺旋和超螺旋形成致密的染色体组结构。结构。vEach long strand of DNA combine with histones and nonhistone proteins to make up the substance c

6、hromatin.v每个长链每个长链DNA与组蛋白和非组蛋白一起构成与组蛋白和非组蛋白一起构成染色质物质。染色质物质。 2022-4-69vA pictorial display of an organisms chromosomes in the coiled, condensed state is known as a karyotype.v生物体中的致密的超螺旋状态的染色体的表型称为核生物体中的致密的超螺旋状态的染色体的表型称为核型型.vKaryotype reveal that in most cells all but sex chromosomes are present as t

7、wo copies, referred to as homologous pairs. v表型显示：在大多数细胞里，除了性染色体外，其它表型显示：在大多数细胞里，除了性染色体外，其它的染色体都是成对出现的，称之为同源染色体对。的染色体都是成对出现的，称之为同源染色体对。2022-4-610homologous pair 同源染色体对Chromosomes that pair during meiosis. Each homologous is a duplicate of one of the chromosomes contributed at syngamy(融合生融合生殖，有性生殖殖，有

8、性生殖)by the mother or father. Homologous chromosomes contain the same linear sequence of genes and as a consequence each gene is present in duplicate.2022-4-611vNon-sex chromosomes are called autosomes. v非性染色体称常染色体。非性染色体称常染色体。vOrganisms whose cells contain two sets of parental chromosomes are called

9、diploid; those with cells containing a single set of parental chromosomes are called haploid.v细胞里含有两套亲本染色体的生物体称二倍细胞里含有两套亲本染色体的生物体称二倍体；细胞里含有单套染色体的生物体称单倍体；细胞里含有单套染色体的生物体称单倍体。体。2022-4-6122. The cell cycle细胞周期细胞周期2022-4-613vimmortal adj.不朽的不朽的vChalone n.生化生化抑素抑素vprophase n. (细胞分裂细胞分裂)前期前期vchromatid n.生物

10、生物染色单体染色单体vcentromere n.生生着丝点着丝点, 着丝粒着丝粒vmetaphase n.中期中期vanaphase n.生生(细胞分裂的细胞分裂的)后期后期2022-4-614vThe cell cycle is a regular sequence in which the cell grows, prepares for division, and divides to form two daughter cells, each of which then repeats the cycle.v细胞周期遵循特定的程序：细胞生长，分裂细胞周期遵循特定的程序：细胞生长，分裂准

11、备，分裂成准备，分裂成2个子细胞，每个子细胞再循环。个子细胞，每个子细胞再循环。 vSuch cycling in effect makes single-celled organisms immortal. v此循环可以有效的使得单细胞生物永生。此循环可以有效的使得单细胞生物永生。 2022-4-615vMany cells in multicellular organisms, including animal muscle and nerve cells, either slow the cycle or break out of it altogether.v多细胞生物中的许多细胞，包

12、括动物肌肉和神多细胞生物中的许多细胞，包括动物肌肉和神经细胞，要么减慢周期速度，要么一起脱离细经细胞，要么减慢周期速度，要么一起脱离细胞周期。胞周期。vThe normal cell cycle consists of four phases. v正常细胞周期由正常细胞周期由4个时期组成。个时期组成。2022-4-616vThe first three include G1, the period of normal metabolism; S phase, during which normal synthesis of biological molecules continues, DNA

13、 is replicated, and histones are synthesized; and G2, a brief period of metabolism and additional growth. v前三个时期包括前三个时期包括G1,正常新陈代谢时期；正常新陈代谢时期；S期期,生物生物分子的合成继续，同时，分子的合成继续，同时，DNA复制，组蛋白合成；复制，组蛋白合成； G2 期，新陈代谢和进一步生长的短暂时期。期，新陈代谢和进一步生长的短暂时期。vTogether the G1, S, and G2 phases are called interphase. vG1, S, 和

14、和G2一起称为分裂间期。一起称为分裂间期。2022-4-617vThe fourth phase of the cell cycle is M phase, the period of mitosis, during which the replicated chromosomes condense and move and the cell divides. v细胞周期的第四个时期是细胞周期的第四个时期是M期，有丝期，有丝分裂期，复制的染色体浓缩，移动并分裂期，复制的染色体浓缩，移动并细胞分裂。细胞分裂。2022-4-618vIt is believed that properties of

15、 the cell cytoplasm control the cell cycle, along with external stimulators and inhibitors such as chalones.v据称是细胞质中的物质与外来的激活因子和据称是细胞质中的物质与外来的激活因子和抑制因子如抑素等一起控制了细胞周期。抑制因子如抑素等一起控制了细胞周期。 2022-4-6193. Mitosis: partitioning the hereditary material有丝分裂：有丝分裂：遗传物质的分离遗传物质的分离2022-4-620vTelophase n.生生(细胞有丝分裂的细

16、胞有丝分裂的)末期末期vkinetochore n.生生动粒动粒, 着丝粒着丝粒, 着丝着丝点点vcytokinesis n.胞质分裂胞质分裂vpinching v.收聚收聚vcell plate 细胞板细胞板vmitosis n.有丝分裂有丝分裂vmeiosis n.减数分裂减数分裂, 成熟分裂成熟分裂2022-4-621vBiologists divide the mitotic cycle into four phases. v生物学家将有丝分裂划分为生物学家将有丝分裂划分为4个阶段。个阶段。vAt the beginning of prophase the chromosomes ea

17、ch consist of two highly condensed chromatids attached to each other at a centromere. v分裂前期，每个染色体是由高度浓缩的通过分裂前期，每个染色体是由高度浓缩的通过着丝粒连接在一起的两个染色单体组成。着丝粒连接在一起的两个染色单体组成。(分分裂前期，高度浓缩的两个染色单体通过着丝裂前期，高度浓缩的两个染色单体通过着丝粒连接在一起形成染色体粒连接在一起形成染色体)2022-4-622v纺锤丝出现：纺锤丝出现：vThe spindles begin to occur.v前期末核仁核膜的消失：前期末核仁核膜的消失：

18、 nuclear envelope have dispersed and nucleoli broken down at the end of prophase.2022-4-623vAs prophase ends and metaphase begins, the condensed chromosomes become associated with the spindle.v分裂前期结束，紧接着是分裂中期，浓缩的分裂前期结束，紧接着是分裂中期，浓缩的染色体与纺锤体相连。染色体与纺锤体相连。(在分裂前期后期和分在分裂前期后期和分裂中期前期，浓缩的染色体与纺锤体相连裂中期前期，浓缩的染色体

19、与纺锤体相连)vEventually the chromosomes become arranged in a plane (called the metaphase plate) at a right angle to the spindle fiber.v最后染色体在纺锤丝的牵引下以最后染色体在纺锤丝的牵引下以正确的角度正确的角度排列在赤道板上。排列在赤道板上。2022-4-624vNext, during anaphase, the two sister chromatids of each chromosome split, and one from each pair is draw

20、n toward each pole of the cell.v在分裂后期，两个姊妹染色单体分离，分别被在分裂后期，两个姊妹染色单体分离，分别被拉向细胞两极。拉向细胞两极。 2022-4-625During telophase nuclear envelope begin to form around each set of chromosomes, and division of the cytoplasm takes place. 在分裂末期，在每套染色体周围形成核膜，在分裂末期，在每套染色体周围形成核膜，细胞质分裂发生细胞质分裂发生。Each chromatids reaches a p

21、ole of the cell.染色体到达两极染色体到达两极.2022-4-626vAs mitosis proceeds, the spindle microtubules play a crucial role in ensuring that both paired and separated chromatids move in the right directions at the proper times.v在有丝分裂过程中，纺锤体微管在确保染色单在有丝分裂过程中，纺锤体微管在确保染色单体配对和在适当时间以正确方向进行分离中发体配对和在适当时间以正确方向进行分离中发挥了关键性的作用

22、。挥了关键性的作用。 vEach half of the spindle forms as microtubules extend from each pole of a dividing cell to the region of the metaphase plate.v微管从正在分裂的细胞两极向赤道板延伸，微管从正在分裂的细胞两极向赤道板延伸，就就形成了纺锤体的一半。形成了纺锤体的一半。v 2022-4-627v During prophase, other microtubules, the centromeric fiber, extend outward from the spin

23、dle poles to structures on the chromosomes called kinetochores. v在分裂前期，其它微管，着丝粒纤维从纺锤体的两在分裂前期，其它微管，着丝粒纤维从纺锤体的两极延伸到染色体的动粒区域。极延伸到染色体的动粒区域。vDuring anaphase the fibers begin to shorten, and the chromatids begin to move apart.在分裂后期，纤维开始变短，染色单体分离在分裂后期，纤维开始变短，染色单体分离。2022-4-628着丝粒（着丝粒（centromere）：）：位于染色体缢缩部位

24、，是位于染色体缢缩部位，是异染色质，是在染色体最异染色质，是在染色体最后复制的部位。着丝粒在后复制的部位。着丝粒在染色体上的位置是确定的。染色体上的位置是确定的。动粒（动粒（kinetochore）：位）：位于着丝粒外侧的蛋白质复于着丝粒外侧的蛋白质复合体。合体。2022-4-629vThe spindle forms differently in plant and animal cells. 植物和动物细胞中的纺锤体的形成是不同的。植物和动物细胞中的纺锤体的形成是不同的。In animal it is associated with centriole, while in plant an

25、d fungal cells spindle formation is associated with regions called microtubule organizing centers. 在动物中，纺锤体的形成与中心粒相关，而在在动物中，纺锤体的形成与中心粒相关，而在植物和真菌细胞中，纺锤体的形成与微管组织植物和真菌细胞中，纺锤体的形成与微管组织中心相关。中心相关。 2022-4-6304. Cytokinesis: Partitioning the cytoplasm胞质分裂：细胞质分离胞质分裂：细胞质分离2022-4-631vThe division of the cell cy

26、toplasm at the end of mitosis is called cytokinesis. v在有丝分裂结束时，细胞质的分裂称为在有丝分裂结束时，细胞质的分裂称为胞质分裂。胞质分裂。vIn animal cells it takes place as a ring of actin filaments contracts around the cell equator, pinching the cell in two. v 在动物细胞中，在动物细胞中，环形的肌动蛋白环形的肌动蛋白纤维围纤维围绕赤道板收缩，将细胞一分为二。绕赤道板收缩，将细胞一分为二。2022-4-632vIn

27、plant cells, which are bounded by a cell wall, cytokinesis involves the building of a new cell plate across the dividing cell at its equator.v在植物细胞中，被细胞壁包围，胞质分裂涉及到在植物细胞中，被细胞壁包围，胞质分裂涉及到在在正在分裂的细胞的赤道板上正在分裂的细胞的赤道板上新的细胞板的形成。新的细胞板的形成。 (在植物细胞中，在赤道板形成新的细胞板。在植物细胞中，在赤道板形成新的细胞板。 )vCell wall material is then de

28、posited in the region of the cell plate.v然后，细胞壁材料在细胞板区域沉积然后，细胞壁材料在细胞板区域沉积2022-4-633Operation of the Contractile Ringduring Cytokinesis2022-4-634 5. Meiosis: the basis of sexual reproduction减数分裂：有性生殖的基础减数分裂：有性生殖的基础2022-4-635vHalving 对分对分, 二等分二等分, 减半减半vSynapsis 联会联会vsynaptinemal complex 联会复合物联会复合物2022

29、-4-636vMeiosis is a special form of cell division that takes place in the reproductive organs that produce sex cells. v减数分裂是发生在产生性细胞的生殖器官中的一种减数分裂是发生在产生性细胞的生殖器官中的一种特殊的分裂形式。特殊的分裂形式。(减数分裂是性细胞分裂的特殊形减数分裂是性细胞分裂的特殊形式。式。 )vLike mitosis, it takes place after DNA replication has occurred and involves two sequ

30、ential nuclear divisions (meiosis I and meiosis II). v如有丝分裂，它也是发生在如有丝分裂，它也是发生在DNA复制后，并有两个复制后，并有两个连续的核分裂。连续的核分裂。2022-4-637vThese division results in four daughter cells, each with half the number of chromosomes of the parent cell. v减数分裂产生减数分裂产生4个子细胞，分别含有亲本一半个子细胞，分别含有亲本一半的染色体数。的染色体数。vThe phenomenon of

31、 crossing over during meiosis results in exchange of genetic information between chromosomes. v在减数分裂中的交换现象导致染色体之间的在减数分裂中的交换现象导致染色体之间的遗传信息交换遗传信息交换。2022-4-638vHence, the homologous chromosome distributed to different progeny cells are not identical.v因此，分配到不同子细胞中的同源染色因此，分配到不同子细胞中的同源染色体是不相同的。体是不相同的。2022

32、-4-639vAs in mitosis two chromatids exist for each chromosome at the beginning of prophase I. v正如在有丝分裂中一样，在前期正如在有丝分裂中一样，在前期I开开始的时候每个染色体是以两个染色始的时候每个染色体是以两个染色单体形式存在单体形式存在2022-4-640v细线期细线期： leptotene: vchromosomes condense highly;偶线期偶线期： zygotene:联会联会： The homologous chromosomes pair all along their le

33、ngth. The process of forming these complexes of homologous chromosomes is called synapsis. This is first feature of meiosis.2022-4-641vThe structure of the synaptinemal complex is present between the homologous chromosomesv联会复合体位于同源染色体之间联会复合体位于同源染色体之间：v粗线期粗线期：pachytene vThe paired homologous chromos

34、omes continue to condense, and each pair is called bivalent. Each pair of homologous chromosomes contains four chromatids, and it is called tetrad.v配对的同源染色体被称为二价体，每条染色体包含4条染色单体，因此称为四价体：2022-4-642v双线期双线期：diplotene vCrossing over can occur between nonsister chromatids. Meiosis results in the genetic e

35、xchanges of maternal and paternal chromosomes. This is second feature of meiosis.非姐们染色体之间发生交换，这导致父母本的遗传物质发生交换，这是减数分裂的第二特点。2022-4-643vDuring this phase the homologous chromosomes undergo synapsis, or pairing, which is brought about by a bridging structure of proteins and RNA called the synaptinemal c

36、omplex.v在这个时期，同源染色体通过蛋白质和在这个时期，同源染色体通过蛋白质和RNA桥配对形成联会复合体。桥配对形成联会复合体。vThe homologous pairs stay together when they align on the metaphase plate.v同源染色体对一起成线形排列在中期赤道同源染色体对一起成线形排列在中期赤道板上。板上。2022-4-644vUnlike the anaphase of mitosis, however, during anaphase I the two chromatids of each chromosome stay jo

37、ined at the centromere and move together to one of the two poles of the cell. 但是，与有丝分裂后期不同的是，在后期但是，与有丝分裂后期不同的是，在后期I，每组染，每组染色体的两个染色单体连接在着丝点上并一起移向细胞色体的两个染色单体连接在着丝点上并一起移向细胞两极的一极。两极的一极。vIt is this event that results in the halving of the chromosome number in the four daughter cells that result from meio

38、sis.v由此而导致由此而导致4个子细胞中染色体数减半。个子细胞中染色体数减半。2022-4-645vDuring telophase I nuclear envelopes enclose the chromosomes in nuclei, and in most species cytokinesis (the first nuclear division) follows. v在末期在末期I，核被膜围绕着细胞核里的染色体，在大多，核被膜围绕着细胞核里的染色体，在大多数物种里第一次数物种里第一次胞质分裂紧随其后胞质分裂紧随其后vThe second nuclear division be

39、gins with metaphase II, in which the chromosomes in each daughter cell again align on a metaphase platev第二次核分裂开始于分裂中期第二次核分裂开始于分裂中期II ，子细胞中染色体，子细胞中染色体再次重新排列在赤道板上。再次重新排列在赤道板上。 2022-4-646vThe centromeres finally divide, and each sister chromatid moves to one of the poles of the spindle.v着丝粒最终分离，每个姊妹染色单

40、体移向两极。着丝粒最终分离，每个姊妹染色单体移向两极。vThe next phase is telophase II, followed again by cytokinesis.v下一个时期是末期下一个时期是末期II，紧接着是第二次，紧接着是第二次胞质分裂。胞质分裂。v The result of the entire process is four haploid cells in which parental chromosomes are randomly distributed. v整个减数分裂过程，产生整个减数分裂过程，产生4个亲本染色体随机分配的个亲本染色体随机分配的单倍体细胞。单倍体细胞。2022-4-6476. Asexual ver