生物專(zhuān)業(yè)英語(yǔ)翻譯+蔣悟生+第3版

1、Lesson One（4學(xué)時(shí)）Inside the Living Cell: Structure andFunction of Internal Cell Parts1.Cytoplasm: The Dynamic, Mobile Factory細(xì)胞質(zhì)：動(dòng)力工廠(chǎng)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 o

2、utside by the plasma membrane. Organelles are suspended within it, supported by 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

3、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)。2The Nucleus: Information 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

4、 or two organelles-the nucleoli-that play a role in cell division. A pore-perforated 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 v

5、ia 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。3.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 th

6、e cell. Organelles described in this section include ribosomes, the endoplasmic 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(xiàn)粒體和植物細(xì)胞中的質(zhì)體。The number of ribosomes within a cell may range from a

7、 few hundred to many thousands. This quantity reflects the fact that, ribosomes 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 mov

8、e along a strand of mRNA, reading the genetic sequence coded in it 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 pro

9、teins and membrane proteins are usually made in association with 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（其數(shù)量表明了核糖體是細(xì)胞過(guò)程中將氨基酸組裝成蛋白質(zhì)輸出或供細(xì)胞所用的場(chǎng)所）。一個(gè)完整的核糖體由一個(gè)大亞基和一個(gè)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

10、lacy array of membranous sacs, tubules, and vesicles, may be either rough (RER) or smooth (SER). Both types 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，

11、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)胞分裂后所需的核膜。SER lacks polysomes; it is active in the synthesis 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

12、 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)有毒亞物質(zhì)的氧化。這兩種內(nèi)質(zhì)網(wǎng)在細(xì)胞中作為分隔，使特定產(chǎn)品分隔開(kāi)，隨后將他們轉(zhuǎn)移到細(xì)胞內(nèi)外特定的部分或細(xì)胞外。Transport vesicles may carry exportable molecules from the endoplasmic reticulum to another membranous organelle, the Golgi complex. Within the Golgi

13、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 vacuol

14、es appear in plant cells and serve as water reservoirs and storage sites for sugars and other molecules. Vacuoles in animal 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 sub

15、set of vacuoles are the organelles known as lysosomes, which contain digestive enzymes (packaged in lysosomes in the Golgi complex) 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。Mito

16、chondria are the sites of energy-yielding chemical reactions in all cells. In addition, plant cells contain plastids that utilize 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-generat

17、ing enzymes are located. Mitochondria are self-replicating, and probably they are the evolutionary descendants of what were once free-living prokaryotes.線(xiàn)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(xiàn)粒體內(nèi)嵴上提供了很大的表面積并分布著產(chǎn)ATP酶。線(xiàn)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,

18、which lack pigments and serve as storage sites for starch, proteins, and oils; and chromoplasts, which contain pigments. The most important chromoplasts are chloroplasts-organelles that contain the chlorophyll used in photosynthesis. The internal structure of chloroplasts includes stacks of membrane

19、s 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。4.The Cytoskeleton（細(xì)胞骨架）All eukaryotic cells have a cytoskeleton, which is a convoluted latticework of filaments and tubules that a

20、ppears to fill all available space in the cell and provides support for various other organelles. A large portion of the cytoskeleton consists of threadlike microfilaments composed mainly of the contractile protein actin. They are involved in many types of intracellular movements in plant and animal

21、 cells. A second protein, myosin, is involve in the contraction of muscle cells. Another main structural component of the cytoskeleton consists of microtubules, which are composed of the globular protein tubulin and together act as scaffolding that provides a stable cell shape. Cytoskeletal intermed

22、iate filaments appear to impart tensile strength to the cell cytoplasm. Mechanoenzymes such as myosin, dynein, and kinesin 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)

23、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)。5.Cellular Movements（細(xì)胞運(yùn)動(dòng) Although the cytoskeleton provides some stability穩(wěn)固 to cells, its microtubules英maikrutju:bju:l and filaments 絲狀物 and their associa

24、ted proteins enable cells to move by creeping 爬行 or gliding 滑動(dòng). Such movements require a solid固體的 substrate to which the cell can adhere附著 and can be guided by the geometry dimitri 幾何形狀of the surface. Some cells also exhibit izibit 展覽 chemotaxis, kemtksis趨藥性 the ability to move toward or away from t

25、he source of a diffusing 擴(kuò)散 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, propelled by whiplike cilia sili纖毛or flagella 英fldel鞭毛. Both cilia and flagella have the same internal struc

26、ture: 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 only from the cell surface where a basal body基體is located. Movement is based on the activiti

27、es of tiny dynein動(dòng)力蛋白 side arms that extend from one of the microtubules of each doublet成對(duì)的東西.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, proteins, and other materials within most plant cells are moved about via cytoplasm

28、ic streaming. The process occurs as myosin maiusin肌凝蛋白 proteins attached to organelles 細(xì)胞器,小器官 push against microfilaments arrayed rei 展示throughout the cell. Microfilaments and microtubules are responsible for almost all major cytoplasmic movements. During cell division, microtubules of the spindle

29、assembled 集合, 收集 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。課后作業(yè)：第一第二篇閱讀材料答案：1B,2C,3B,4B,5D,6c; 1A,2B,3D,4ALesson Two（2學(xué)時(shí)）PhotosynthesisPhotosynthes

30、is occurs only in the chlorophyllchlorophyll葉綠素-containing cells of green plants, algae藻, and certain protists 原生生物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 t

31、he opposite of cellular respiration. Whereas 然而 cellular細(xì)胞的 respiration 呼吸is highly exergonic吸收能量的 and releases energy, photosynthesis光合作用 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。總體來(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)

32、程。Photosynthesis starts with CO2 and H2O as raw materials and proceeds through two sets of partial reactions. In the first set, called the light-dependent reactions, water molecules are split裂開(kāi) (oxidized), 02 is released, and ATP and NADPH are formed. These reactions must take place in the presence

33、of 在面前 light energy. In the second set, called light-independent 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

34、。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ATP。Both sets of reactions take place in chloroplasts. Most of the enzymes and pigments 色素for the lightdependent reactions are embedded 深入的 內(nèi)含的in the thylakoid類(lèi)囊體 membrane膜 隔膜 of chloroplasts 葉綠體. The dark reactions take place in the stroma

35、.基質(zhì) 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 Photosynthetic 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 withi

36、n a particular absorption spectrums statement of the amount of light absorbed by chlorophyll 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 sta

37、te to a less-stable excited state. During the light-dependent reactions of photosynthesis, 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

38、。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 various 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

39、pigment molecules is funneled to a special chlorophyll a molecule, termed 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 a

40、nd an electron donor. These aggregations are known respectively as photosystem (P700) and photosystem (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(xiàn)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)和光合系統(tǒng) 。The Light-Dependent Reaction

41、: Converting Solar Energy into Chemical-Bond Energy光反應(yīng)：光能轉(zhuǎn)化成化學(xué)鍵能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

42、 light strikes the P680 reaction center in photosystem . In this 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 e

43、lectrons that pass down the chain, two ATPs are formed. The last acceptor in the chain is the P700 reaction center of photosystem . 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

44、to the NADPH. The ATP generated previously and the NADPH then 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)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)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NA

45、DPH。早期產(chǎn)生的ATP和NADPH進(jìn)入暗反應(yīng)。The production of ATP from the 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 A

46、TP through cyclic photophosphorylation, in which some electrons are shunted back through the electron transport chain between photosystems and .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)流經(jīng)光合系統(tǒng)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)和之間的電子傳遞鏈中回流。The Light-Independent Reactions: Building Carbohydrates暗反應(yīng)：碳水

47、化合物的形成In the light-independent reactions of 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 enzym

48、e ribulose biphosphate carboxylase. The reduction 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 photos

49、ynthesis（氧：光合作用的抑制因子）High levels of 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 plan

50、ts; they experience decreased carbohydrate 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 carr

51、ying out photosynthesis only in cells 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。課后作業(yè)：第一篇閱讀材料答案：1B,2A,3A,4D,5C,6cLesson Three（2學(xué)時(shí)）Cellular Reproduction:

52、 Mitosis and MeiosisThe Nucleus and ChromosomesThe cell nucleus is the main repository of genetic information. Within the nucleus 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 protein

53、s, or histones, forming beadlike complexes known as nucleosomes. More coiling and supercoiling produces a dense chromosome structure. 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(xiàn)以及相關(guān)的成簇蛋白質(zhì)。DNA螺旋線(xiàn)纏繞成簇的組蛋白形成珠鏈狀的核小體。

54、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 organisms chromosomes in the coiled, condensed 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

55、 autosomes. Organisms whose cells contain two sets of parental chromosomes are called diploid; those with cells containing 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 cyc

56、le 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. Such cycling in effect makes single-celled organisms immortal. Many cells in multicellular organisms, including animal muscle and nerve cells, either

57、 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 m

58、olecules continues, DNA is replicated, and histones are synthesized; and G2, a brief period of metabolism and additional 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, along 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