生物專(zhuān)業(yè)英語(yǔ)課本學(xué)習(xí)知識(shí)翻譯

1、、第一課Cytoplasm: The Dynamic, Mobile Factory 細(xì)胞質(zhì)：動(dòng)力工廠Most of the properties we associate with life are properties of the cytoplasm. Much of the mass of a cell consists of this semifluid substance, which is bounded on the outside by the plasma membrane. Organelles are suspended within it, supported by

2、the filamentous network of the cytoskeleton. Dissolved in the cytoplasmic fluid are nutrients, ions, soluble proteins, and other materials needed for cell functioning.生命的大部分特征表現(xiàn)在細(xì)胞質(zhì)的特征上。細(xì)胞質(zhì)大部分由半流體物質(zhì)組成，并由細(xì)胞膜(原生質(zhì)膜)包被。細(xì)胞器懸浮在其中，并由絲狀的細(xì)胞骨架支撐。細(xì)胞質(zhì)中溶解了大量的營(yíng)養(yǎng)物質(zhì)，離子，可溶蛋白以及維持細(xì)胞生理需求的 其它物質(zhì)。The Nucleus: Information

3、Central (細(xì)胞核：信息中心)The eukaryotic cell nucleus is the largest organelle and houses the genetic material (DNA) on chromosomes. (In prokaryotes the hereditary material is found in the nucleoid.) The nucleus also contains one or two organelles-the nucleoli-that play a role in cell division. A pore-perfo

4、rated sac called the nuclear envelope separates the nucleus and its contents from the cytoplasm. Small molecules can pass through the nuclear envelope, but larger molecules such as mRNA and ribosomes must enter and exit via the pores. 真核細(xì)胞的細(xì)胞核是最大的細(xì)胞器，細(xì)胞核對(duì)染色體組有保護(hù)作用(原核細(xì)胞的遺傳物質(zhì)存在于擬核中)。細(xì)胞核含有一或二個(gè)核仁，核仁促進(jìn)細(xì)胞

5、分裂。核膜貫穿許多小孔，小分子可以自由通過(guò)核膜，而象mRNA 和核糖體等大分子必須通過(guò)核孔運(yùn)輸。Organelles: Specialized Work Units (細(xì)胞器：特殊的功能單位)All eukaryotic cells contain most of the various kinds of organelles, and each organelle performs a specialized function in the cell. Organelles described in this section include ribosomes, the endoplasmi

6、c reticulum, the Golgi complex, vacuoles, lysosomes, mitochondria, and the plastids of plant cells.所有的真核細(xì)胞都含有多種細(xì)胞器，每個(gè)細(xì)胞器都有其特定功能。本節(jié)主要介紹核糖體，內(nèi)質(zhì)網(wǎng)，高爾基體系，液泡， 溶酶體，線粒體和植物細(xì)胞中的質(zhì)體。The number of ribosomes within a cell may range from a few hundred to many thousands. This quantity reflects the fact that, ribosom

7、es are the sites at which amino acids are assembled into proteins for export or for use in cell processes. A complete ribosome is composed of one larger and one smaller subunit. During protein synthesis the two subunits move along a strand of mRNA, "reading" the genetic sequence coded in i

8、t and translating that sequence into protein. Several ribosomes may become attached to a single mRNA strand; such a combination is called a polysome. Most cellular proteins are manufactured on ribosomes in the cytoplasm. Exportable proteins and membrane proteins are usually made in association with

9、the endoplasmic reticulum.核糖體的數(shù)量變化從幾百到幾千，核糖體是氨基酸組裝成蛋白質(zhì)的重要場(chǎng)所。完整的核糖體由大亞基和小亞基組成。核糖體沿著mRNA 移動(dòng)并閱讀遺傳密碼，翻譯成蛋白質(zhì)。一條 mRNA 上可能有多個(gè)核糖體，稱(chēng)多聚核糖體。大多數(shù)細(xì)胞蛋白是由細(xì)胞質(zhì)中核糖體生產(chǎn)。輸出蛋白和膜蛋白通常與內(nèi)質(zhì)網(wǎng)有關(guān)。The endoplasmic reticulum, a lacy array of membranous sacs, tubules, and vesicles, may be either rough (RER) or smooth (SER). Both type

10、s play roles in the synthesis and transport of proteins. The RER, which is studded with polysomes, also seems to be the source of the nuclear envelope after a cell divides.內(nèi)質(zhì)網(wǎng)，帶有花邊的生物囊，有管狀，泡狀之分，以及光滑和粗糙面區(qū)別。兩種都與蛋白質(zhì)的合成和運(yùn)輸有關(guān)。粗糙 內(nèi)質(zhì)網(wǎng)上分布許多核糖體，也可能提供細(xì)胞分裂后所需的細(xì)胞膜。SER lacks polysomes; it is active in the synthe

11、sis of fats and steroids and in the oxidation of toxic substances in the cell. Both types of endoplasmic reticulum serve as compartments within the cell where specific products can be isolated and subsequently shunted to particular areas in or outside the cell.光滑內(nèi)質(zhì)網(wǎng)上無(wú)核糖體，主要作用是脂肪和類(lèi)固醇的合成以及細(xì)胞內(nèi)有毒物質(zhì)的氧化。兩

12、種內(nèi)質(zhì)網(wǎng)合成的產(chǎn)物在其中 進(jìn)行分流或運(yùn)輸?shù)郊?xì)胞外。Transport vesicles may carry exportable molecules from the endoplasmic reticulum to another membranous organelle, the Golgi complex. Within the Golgi complex molecules are modified and packaged for export out of the cell or for delivery else where in the cytoplasm.運(yùn)輸小泡能夠?qū)⒖蛇\(yùn)輸

13、分子從內(nèi)質(zhì)網(wǎng)運(yùn)輸?shù)礁郀柣鶑?fù)合體上。在高爾基復(fù)合體中修飾，包裝后輸出細(xì)胞或傳遞到細(xì)胞 質(zhì)中的其他場(chǎng)所。Vacuoles in cells appear to be hollow sacs but are actually filled with fluid and soluble molecules. The most prominent vacuoles appear in plant cells and serve as water reservoirs and storage sites for sugars and other molecules. Vacuoles in animal

14、cells carry out phagocytosis (the intake of particulate matter) and pinocytosis (vacuolar drinking).細(xì)胞中的液泡好象是中空的，但實(shí)際上充滿(mǎn)了液體和可溶分子。最典型的液泡存在于植物細(xì)胞中，儲(chǔ)備水，糖以及其 它分子。動(dòng)物中的液泡起吞噬和胞飲作用。A subset of vacuoles are the organelles known as lysosomes, which contain digestive enzymes (packaged in lysosomes in the Golgi c

15、omplex) that can break down most biological macromolecules. They act to digest food particles and to degrade damaged cell parts.溶酶體是液泡亞單位，含有消化酶，降解大部分生物大分子。消化食物微粒和降解損傷的細(xì)胞殘片。Mitochondria are the sites of energy-yielding chemical reactions in all cells. In addition, plant cells contain plastids that ut

16、ilize light energy to manufacture carbohydrates in the process of photosynthesis. It is on the large surface area provided by the inner cristae of mitochondria that ATP-generating enzymes are located. Mitochondria are self-replicating, and probably they are the evolutionary descendants of what were

17、once free-living prokaryotes.線粒體是細(xì)胞中化學(xué)產(chǎn)能的場(chǎng)所。另外，植物細(xì)胞中的質(zhì)體在光合作用中利用光能產(chǎn)生碳水化合物，線粒體內(nèi)嵴上提供了很大的表面積并分布著產(chǎn)ATP 酶。線粒體自我復(fù)制，并且可能是自由生活的原核生物在進(jìn)化中形成的后代。There are two types of plastids: leucoplasts, which lack pigments and serve as storage sites for starch, proteins, and oils; and chromoplasts, which contain pigments. Th

18、e most important chromoplasts are chloroplasts-organelles that contain the chlorophyll used in photosynthesis. The internal structure of chloroplasts includes stacks of membranes called grana, which are embedded in a matrix called the stroma.質(zhì)體有兩種類(lèi)型：白色體，缺乏色素，是淀粉，蛋白質(zhì)和油的儲(chǔ)備場(chǎng)所；色質(zhì)體，含有色素。葉綠體是最重要的色質(zhì)體，含有與光合

19、作用有關(guān)的葉綠素。葉綠體的內(nèi)部結(jié)構(gòu)是由多層膜形成的葉綠體基粒，其中包埋在基質(zhì)中的基粒稱(chēng)子 座。The Cytoskeleton (細(xì)胞骨架)All eukaryotic cells have a cytoskeleton, which is a convoluted latticework of filaments and tubules that appears to fill all available space in the cell and provides support for various other organelles. A large portion of the cy

20、toskeleton consists of threadlike microfilaments composed mainly of the contractile protein actin. They are involved in many types of intracellular movements in plant and animal cells. A second protein, myosin, is involve in the contraction of muscle cells. Another main structural component of the c

21、ytoskeleton consists of microtubules, which are composed of the globular protein tubulin and together act as scaffolding that provides a stable cell shape. Cytoskeletal intermediate filaments appear to impart tensile strength to the cell cytoplasm. Mechanoenzymes such as myosin, dynein, and kinesin

22、interact with the cytoskeletal filaments and tubules to generate forces that cause movements.所有的細(xì)胞都有細(xì)胞骨架，網(wǎng)絡(luò)結(jié)構(gòu)的纖絲充滿(mǎn)了它所能觸及的全部空間并且對(duì)細(xì)胞器提供支持作用。細(xì)胞骨架大部分由微絲組成，微絲主要由可收縮的肌動(dòng)蛋白組成。動(dòng)植物細(xì)胞的許多種類(lèi)型細(xì)胞內(nèi)運(yùn)動(dòng)與肌動(dòng)蛋白有關(guān)。第二類(lèi)蛋白是肌球蛋白，它與肌肉細(xì)胞的收縮有關(guān)。細(xì)胞骨架的另一個(gè)主要結(jié)構(gòu)成分是微管，由球狀的微管蛋白組成，象腳手 架一般維持細(xì)胞的穩(wěn)定形態(tài)。細(xì)胞骨架的中間絲提供了細(xì)胞質(zhì)伸縮動(dòng)力。機(jī)械酶，例如，肌球蛋白，動(dòng)力蛋白，驅(qū)動(dòng) 蛋

23、白與微絲，微管相互作用產(chǎn)生動(dòng)力而引起細(xì)胞運(yùn)動(dòng)。Cellular Movements (細(xì)胞運(yùn)動(dòng))Although the cytoskeleton provides some stability to cells, its microtubules and filaments and their associated proteins enable cells to move by creeping or gliding. Such movements require a solid substrate to which the cell can adhere and can be guide

24、d by the geometry of the surface. Some cells also exhibit chemotaxis, the ability to move toward or away from the source of a diffusing chemical.盡管細(xì)胞骨架提供了細(xì)胞的某些穩(wěn)定性，微絲，微管及相關(guān)蛋白能使細(xì)胞爬行或滑動(dòng)。這種運(yùn)動(dòng)需要固體基質(zhì)依托并通過(guò)表面幾何形狀的改變而運(yùn)動(dòng)。某些細(xì)胞具備趨藥性，即趨向或逃離擴(kuò)散開(kāi)的化學(xué)源。Certain eukaryotic cells can swim freely in liquid environments,

25、propelled by whiplike cilia or flagella. Both cilia and flagella have the same internal structure: nine doublets (pairs of microtubules) are arranged in a ring and extend the length of the cilium or flagellum, and two more microtubules run down the center of the ring. Every cilium or flagellum grows

26、 only from the cell surface where a basal body is located. Movement is based on the activities of tiny dynein side arms that extend from one of the microtubules of each doublet.某些真核細(xì)胞能在液體液體中自由運(yùn)動(dòng)，由纖毛或鞭毛推動(dòng)。纖毛和鞭毛具有同樣的內(nèi)部結(jié)構(gòu)：九個(gè)雙微管環(huán)形排列，縱向延伸，環(huán)中心是兩個(gè)或以上微管組成。纖毛或鞭毛從細(xì)胞表面的基體出生長(zhǎng)，雙微管的動(dòng)力蛋白臂從一側(cè)延伸到 另一側(cè)而引起運(yùn)動(dòng)。Nutrients,

27、 proteins, and other materials within most plant cells are moved about via cytoplasmic streaming. The process occurs as myosin proteins attached to organelles push against microfilaments arrayed throughout the cell. Microfilaments and microtubules are responsible for almost all major cytoplasmic mov

28、ements. During cell division, microtubules of the spindle assembled from tubutin subunits near organelles called centrioles move the chromosomes.大部分植物細(xì)胞的營(yíng)養(yǎng)，蛋白質(zhì)和其它物質(zhì)由細(xì)胞質(zhì)流運(yùn)輸。這個(gè)過(guò)程是由于依附在細(xì)胞器上的肌球蛋白反推排列在細(xì)胞周?chē)奈⒔z形成的。絕大部分細(xì)胞質(zhì)運(yùn)動(dòng)由微絲和微管完成。在細(xì)胞分裂期間，中心粒周?chē)挠晌⒐艿鞍讈喕b配形成的紡錘體微管移向染色體。第二課Photosynthesis occurs only in the c

29、hlorophyll-containing cells of green plants, algae, and certain protists and bacteria. Overall, it is a process that converts light energy into chemical energy that is stored in the molecular bonds. From the point of view of chemistry and energetics, it is the opposite of cellular respiration. Where

30、as cellular respiration is highly exergonic and releases energy, photosynthesis requires energy and is highly endergonic.光合作用只發(fā)生在含有葉綠素的綠色植物細(xì)胞，海藻，某些原生動(dòng)物和細(xì)菌之中?？傮w來(lái)說(shuō)，這是一個(gè)將光能轉(zhuǎn)化成化學(xué)能，并將能量貯存在分子鍵中，從化學(xué)和動(dòng)能學(xué)角度來(lái)看，它是細(xì)胞呼吸作用的對(duì)立面。細(xì)胞呼吸作用是高度放能的，光合作用是需要能量并高吸能的過(guò)程。Photosynthesis starts with CO2 and H2O as raw materials a

31、nd proceeds through two sets of partial reactions. In the first set, called the light-dependent reactions, water molecules are split (oxidized), 02 is released, and ATP and NADPH are formed. These reactions must take place in the presence of light energy. In the second set, called light-independent

32、reactions, CO2 is reduced (via the addition of H atoms) to carbohydrate. These chemical events rely on the electron carrier NADPH and ATP generated by the first set of reactions.光合作用以二氧化碳和水為原材料并經(jīng)歷兩步化學(xué)反應(yīng)。第一步， 稱(chēng)光反應(yīng)，水分子分解，氧分子釋放，ATP 和 NADPH形成。此反應(yīng)需要光能的存在。第二步，稱(chēng)暗反應(yīng)，二氧化碳被還原成碳水化合物，這步反應(yīng)依賴(lài)電子載體NADPH以及第一步反應(yīng)產(chǎn)生的AT

33、P。Both sets of reactions take place in chloroplasts. Most of the enzymes and pigments for the lightdependent reactions are embedded in the thylakoid membrane of chloroplasts. The dark reactions take place in the stroma.兩步反應(yīng)都發(fā)生在葉綠體中。光反應(yīng)需要的大部分酶和色素包埋在葉綠體的類(lèi)囊體膜上。暗反應(yīng)發(fā)生在基質(zhì)中。How Light Energy Reaches Photosy

34、nthetic Cells (光合細(xì)胞如何吸收光能的)The energy in light photons in the visible part of the spectrum can be captured by biological molecules to do constructive work. The pigment chlorophyll in plant cells absorbs photons within a particular absorption spectrums statement of the amount of light absorbed by chl

35、orophyll at different wavelengths. When light is absorbed it alters the arrangement of electrons in the absorbing molecule. The added energy of the photon boosts the energy condition of the molecule from a stable state to a less-stable excited state. During the light-dependent reactions of photosynt

36、hesis, as the absorbing molecule returns to the ground state, the "excess" excitation energy is transmitted to other molecules and stored as chemical energy.生物分子能捕獲可見(jiàn)光譜中的光能。植物細(xì)胞中葉綠素在不同光波下吸收部分吸收光譜。在吸收分子中，光的作用使 分子中的電子發(fā)生重排。光子的能量激活了分子的能量狀態(tài)，使其從穩(wěn)定態(tài)進(jìn)入不穩(wěn)定的激活態(tài)。All photosynthetic organisms contain v

37、arious classes of chlorophylls and one or more carotenoid (accessory) pigments that also contribute to photosynthesis. Groups of pigment molecules called antenna complexes are present on thylakoids. Light striking any one of the pigment molecules is funneled to a special chlorophyll a molecule, term

38、ed a reaction-center chlorophyll, which directly participates in photosynthesis. Most photosynthetic organisms possess two types of reaction-center chlorophylls, P680 and P700, each associated with an electron acceptor molecule and an electron donor. These aggregations are known respectively as phot

39、osystem I (P700) and photosystem n (P680).所有的光合作用生物含有不同等級(jí)的葉綠素和一個(gè)或多個(gè)類(lèi)胡蘿卜素(光合作用的輔助色素)。稱(chēng)作天線復(fù)合體的色素分子群存在于類(lèi)囊體中。激活色素分子的光能進(jìn)入葉綠素反應(yīng)中心，其直接參與光合作用。大部分光反應(yīng)細(xì)胞器擁有兩套反應(yīng)中心，P680和P700,每個(gè)光系統(tǒng)都含有一個(gè)電子受體和電子供體。這些集合體就是大家熟識(shí)的光合系統(tǒng)I和 光合系統(tǒng)n。The Light-Dependent Reaction: Converting Solar Energy into Chemical-Bond Energy 光反應(yīng)：光能轉(zhuǎn)化成化學(xué)鍵能

40、The photosystems of the light-dependent reactions are responsible for the packaging of light energy in the chemical compounds ATP and NADPH. This packaging takes place through a series of oxidation reduction reactions set in motion when light strikes the P680 reaction center in photosystem n . In th

41、is initial event water molecules are cleaved, oxygen is released, and electrons are donated. These electrons are accepted first by plastoquinone and then by a series of carriers as they descend an electron transport chain. For each four electrons that pass down the chain, two ATPs are formed. The la

42、st acceptor in the chain is the P700 reaction center of photosystem I . At this point incoming photons boost the energy of the electrons, and they are accepted by ferredoxin. Ferredoxin is then reoxidized, and the coenzyme NADP+ is reduced to the NADPH. The ATP generated previously and the NADPH the

43、n take part in the light independent reactions.光反應(yīng)的光系統(tǒng)將光能轉(zhuǎn)化成化學(xué)復(fù)合物ATP和NADPH。當(dāng)光激活光系統(tǒng)H的光反應(yīng)中心時(shí)，通過(guò)一系列的氧化還原反應(yīng)實(shí)現(xiàn)能量的傳遞。反應(yīng)開(kāi)始時(shí)，水被分解，氧被釋放并提供電子。電子首先傳遞給質(zhì)體醌，然后通過(guò)一系列載體形成的電子傳遞鏈。每傳遞4個(gè)電子，形成2個(gè)ATP。最后一個(gè)受體存在于光反應(yīng)系統(tǒng)I的反應(yīng)中心里。此處光子激活電子，電子傳遞給鐵氧還蛋白。鐵氧還蛋白再氧化，并且輔酶NADP +還原成 NADPH 。 早期產(chǎn)生的ATP 和 NADPH進(jìn)入暗反應(yīng)。The production of ATP from t

44、he transport of electrons excited by light energy down an electron transport chain is termed photophosphorylation. The one-way flow of electrons through photosystems II and I is called noncyclic photophosphorylation; plants also derive additional ATP through cyclic photophosphorylation, in which som

45、e electrons are shunted back through the electron transport chain between photosystems n and I .由電子傳遞鏈偶連產(chǎn)生ATP的過(guò)程稱(chēng)為光合磷酸化。通過(guò)光合系統(tǒng)n流經(jīng)光合系統(tǒng)I的電子路徑稱(chēng)非循環(huán)式光合磷酸化；植物通過(guò)循環(huán)式光合磷酸化獲得額外的ATP, 一些電子在光合系統(tǒng)I和n之間的電子傳遞鏈中回流。The Light-Independent Reactions: Building Carbohydrates 暗反應(yīng)：碳水化合物的形成In the light-independent reactions o

46、f photosynthesis, which are driven by ATP and NADPH, C02 is converted to carbohydrate. The reactions are also known as the Calvin-Benson cycle. Atmospheric CO2, is fixed as it reacts with ribulose biphosphate (RuBP), a reaction that is catalyzed by the enzyme ribulose biphosphate carboxylase. The re

47、duction Of C02 to carbohydrate (fructose diphosphate) is completed via several more steps of the cycle. Finally, RUBP is regenerated so that the cycle may continue.由 ATP 和 NADPH 驅(qū)動(dòng)的暗反應(yīng)中，二氧化碳轉(zhuǎn)化成碳水化合物。即卡爾文循環(huán)。二磷酸核酮糖固定二氧化碳，由二 磷酸核酮糖羧化酶催化。Oxygen: An Inhibitor of photosynthesis (氧：光合作用的抑制因子)High levels of

48、oxygen in plant cells can disrupt photosynthesis and can also cause photorespiration-an inefficient fun of the dark reactions in which 02 is fixed rather than C02 and no carbohydrate is produced.Reprieve from Photorespiration: The C4 PathwayMost plants are C3 plants; they experience decreased carboh

49、ydrate production under hot, dry conditions as a result of the effects of photorespiration. Among C4 plants, however, special leaf anatomy and a unique biochemical pathway enable the plant to thrive in and conditions. Thus C4 plants lessen photorespiration by carrying out photosynthesis only in cell

50、s that are insulated from high levels of CO2. They also possess a novel mechanism for carbon fixation.大部分植物是碳3 植物，在高溫干旱條件下，由于光呼吸作用而使碳水化合物的合成降低。而在大多數(shù)的碳4植物中，由于葉脈的特殊構(gòu)造和獨(dú)特的化學(xué)路徑使植物依然很茂盛。這是碳固定的一個(gè)新機(jī)制。第三課The Nucleus and ChromosomesThe cell nucleus is the main repository of genetic information. Within the nu

51、cleus are the chromosomes tightly coiled strands of DNA and clusters of associated proteins. Long stretches of the continuous DNA molecule wind around these clusters of proteins, or histones, forming beadlike complexes known as nucleosomes. More coiling and supercoiling produces a dense chromosome s

52、tructure. Each long strand of DNA combines with histones and nonhistone proteins to make up the substance chromatin.細(xì)胞核是貯藏遺傳信息的主要場(chǎng)所。DNA 盤(pán)繞成螺旋線以及相關(guān)的成簇蛋白質(zhì)。DNA 螺旋線纏繞成簇的組蛋白形成珠鏈狀的核小體。這些螺旋和超螺旋形成致密的染色體組結(jié)構(gòu)。每個(gè)長(zhǎng)鏈DNA 與組蛋白和非組蛋白一起構(gòu)成染色質(zhì)物質(zhì)。A pictorial display of an organism's chromosomes in the coiled, condens

53、ed state is known as a karyotype. Karyotype reveal that in most cells all but sex chromosomes are present as two copies, referred to as homologous pairs. Non-sex chromosomes are called autosomes. Organisms whose cells contain two sets of parental chromosomes are called diploid; those with cells cont

54、aining a single set of parental chromosomes are called haploid.染色體致密的超螺旋狀態(tài)我們稱(chēng)染色體組。除了性染色體外，大多數(shù)細(xì)胞的染色體組成對(duì)出現(xiàn)，稱(chēng)同源染色體對(duì)。非性染色 體稱(chēng)常染色體。生物細(xì)胞含有兩套父母本染色體的稱(chēng)二倍體；含有單套染色體的稱(chēng)單倍體。The Cell CycleThe cell cycle is a regular sequence in which the cell grows, prepares for division, and divides to form two daughter cells, eac

55、h of which then repeats the cycle. Such cycling in effect makes single-celled organisms immortal. Many cells in multicellular organisms, including animal muscle and nerve cells, either slow the cycle or break out of it altogether.在細(xì)胞生長(zhǎng)過(guò)程中，細(xì)胞循環(huán)遵循特定程序，分裂準(zhǔn)備，分裂成2 個(gè)子細(xì)胞，子細(xì)胞再循環(huán)。此循環(huán)使得單細(xì)胞永生。多細(xì)胞生物中的許多細(xì)胞，包括動(dòng)物肌

56、肉和神經(jīng)細(xì)胞，要么降低循環(huán)速度，要么同時(shí)分裂。The normal cell cycle consists of four phases. The first three include G1, the period of normal metabolism; S phase, during which normal synthesis of biological molecules continues, DNA is replicated, and histones are synthesized; and G2, a brief period of metabolism and addit

57、ional growth. Together the G1, S, and G2 phases are called interphase. The 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. It is believed that properties of the cell cytoplasm control the cell cycle, al

58、ong with external stimulators and inhibitors such as chalones.正常細(xì)胞循環(huán)由4 個(gè)時(shí)期組成。頭三期包括G1, 正常新陳代謝；S 期 ,正常新陳代謝同時(shí)，DNA 復(fù)制， 組蛋白合成；G2期，短期的新陳代謝和少許生長(zhǎng)。G1, S, 和 G2 稱(chēng)分裂間期。最后是M 期，有絲分裂期，復(fù)制的染色體組濃縮，移動(dòng)并細(xì)胞分裂。據(jù)稱(chēng)是染色質(zhì)控制了細(xì)胞循環(huán)，伴隨外部激活因子和抑制因子如抑素。Mitosis: Partitioning the Hereditary MaterialBiologists divide the mitotic cycle i

59、nto four phases. At the beginning of prophase the chromosomes each consist of two highly condensed chromatids attached to each other at a centromere. As prophase ends and metaphase begins, the condensed chromosomes become associated with the spindle. Eventually the chromosomes become arranged in a plane (called the metaphase plate) at a right angle to the spindle fibers. Next