生物专业英语课文翻译

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1、-第一课Cytoplasm: The Dynamic, Mobile Factory细胞质：动力工厂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 the

2、 filamentous network of the cytoskeleton.Dissolved in the cytoplasmic fluid are nutrients, ions, soluble proteins, and other materials needed for cell functioning.生命的大局部特征表现在细胞质的特征上。细胞质大局部由半流体物质组成，并由细胞膜原生质膜包被。细胞器悬浮在其中，并由丝状的细胞骨架支撑。细胞质中溶解了大量的营养物质，离子，可溶蛋白以及维持细胞生理需求的其它物质。The Nucleus: Information Central

3、细胞核：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-perforated sac c

4、alled 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 e*it via the pores.真核细胞的细胞核是最大的细胞器，细胞核对染色体组有保护作用原核细胞的遗传物质存在于拟核中。细胞核含有一或二个核仁，核仁促进细胞分裂。核膜贯穿许多小孔，小分子

5、可以自由通过核膜，而象mRNA和核糖体等大分子必须通过核孔运输。Organelles: Specialized Work Units细胞器：特殊的功能单位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 endoplasmic reticulum, the Gol

6、gi ple*, vacuoles, lysosomes, mitochondria, and the plastids of plant cells.所有的真核细胞都含有多种细胞器，每个细胞器都有其特定功能。本节主要介绍核糖体，质网，高尔基体系，液泡，溶酶体，线粒体和植物细胞中的质体。The number of ribosomes within a cell may range from a few hundred to many thousands.This quantity reflects the fact that, ribosomes are the sites at which

7、amino acids are assembled into proteins for e*port or for use in cell processes.A plete ribosome is posed 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 it and translating that sequence into protein.S

8、everal ribosomes may bee attached to a single mRNA strand; such a bination is called a polysome.Most cellular proteins are manufactured on ribosomes in the cytoplasm.E*portable proteins and membrane proteins are usually made in association with the endoplasmic reticulum.核糖体的数量变化从几百到几千，核糖体是氨基酸组装成蛋白质的

9、重要场所。完整的核糖体由大亚基和小亚基组成。核糖体沿着mRNA移动并阅读遗传密码，翻译成蛋白质。一条mRNA上可能有多个核糖体，称多聚核糖体。大多数细胞蛋白是由细胞质中核糖体生产。输出蛋白和膜蛋白通常与质网有关。The endoplasmic reticulum, a 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

10、RER, which is studded with polysomes, also seems to be the source of the nuclear envelope after a cell divides.质网，带有花边的生物囊，有管状，泡状之分，以及光滑和粗糙面区别。两种都与蛋白质的合成和运输有关。粗糙质网上分布许多核糖体，也可能提供细胞分裂后所需的细胞膜。SER lacks polysomes; it is active in the synthesis of fats and steroids and in the o*idation of to*ic substance

11、s in the cell.Both types of endoplasmic reticulum serve as partments within the cell where specific products can be isolated and subsequently shunted to particular areas in or outside the cell.光滑质网上无核糖体，主要作用是脂肪和类固醇的合成以及细胞有毒物质的氧化。两种质网合成的产物在其中进展分流或运输到细胞外。Transport vesicles may carry e*portable molecul

12、es from the endoplasmic reticulum to another membranous organelle, the Golgi ple*.Within the Golgi ple* molecules are modified and packaged for e*port out of the cell or for delivery else where in the cytoplasm.运输小泡能够将可运输分子从质网运输到高尔基复合体上。在高尔基复合体中修饰，包装后输出细胞或传递到细胞质中的其他场所。Vacuoles in cells appear to be

13、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 cells carry out phagocytosis (the intake of particulate matter) and pinocytosis (va

14、cuolar drinking).细胞中的液泡好象是中空的，但实际上充满了液体和可溶分子。最典型的液泡存在于植物细胞中，储藏水，糖以及其它分子。动物中的液泡起吞噬和胞饮作用。A subset of vacuoles are the organelles known as lysosomes, which contain digestive enzymes (packaged in lysosomes in the Golgi ple*) that can break down most biological macromolecules.They act to digest food part

15、icles and to degrade damaged cell parts.溶酶体是液泡亚单位，含有消化酶，降解大局部生物大分子。消化食物微粒和降解损伤的细胞残片。Mitochondria 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

16、 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 once free-living prokaryotes.线粒体是细胞中化学产能的场所。另外，植物细胞中的质体在光合作用中利用光能产生碳水化合物，线粒体嵴上提供了很大的外表积并分布着

17、产ATP酶。线粒体自我复制，并且可能是自由生活的原核生物在进化中形成的后代。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.The most important chromoplasts are chloroplasts-organelles that contain the chlorophyll used in

18、 photosynthesis.The internal structure of chloroplasts includes stacks of membranes called grana, which are embedded in a matri* called the stroma.质体有两种类型：白色体，缺乏色素，是淀粉，蛋白质和油的储藏场所；色质体，含有色素。叶绿体是最重要的色质体，含有与光合作用有关的叶绿素。叶绿体的部构造是由多层膜形成的叶绿体基粒，其中包埋在基质中的基粒称子座。The Cytoskeleton细胞骨架All eukaryotic cells have a cy

19、toskeleton, 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 cytoskeleton consists of threadlike microfilaments posed mainly of the contractile protein actin.They a

20、re 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 ponent of the cytoskeleton consists of microtubules, which are posed of the globular protein tubulin and together act as scaf

21、folding 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 interact with the cytoskeletal filaments and tubules to generate forces that cause movements.所有的细胞都有细胞骨架，网络构造的纤丝充满了

22、它所能触及的全部空间并且对细胞器提供支持作用。细胞骨架大局部由微丝组成，微丝主要由可收缩的肌动蛋白组成。动植物细胞的许多种类型细胞运动与肌动蛋白有关。第二类蛋白是肌球蛋白，它与肌肉细胞的收缩有关。细胞骨架的另一个主要构造成分是微管，由球状的微管蛋白组成，象脚手架一般维持细胞的稳定形态。细胞骨架的中间丝提供了细胞质伸缩动力。机械酶，例如，肌球蛋白，动力蛋白，驱动蛋白与微丝，微管相互作用产生动力而引起细胞运动。Cellular Movements细胞运动Although the cytoskeleton provides some stability to cells, its microtubu

23、les 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 guided by the geometry of the surface.Some cells also e*hibit chemota*is, the ability to move toward or away from the source of

24、 a diffusing chemical.尽管细胞骨架提供了细胞的*些稳定性，微丝，微管及相关蛋白能使细胞爬行或滑动。这种运动需要固体基质依托并通过外表几何形状的改变而运动。*些细胞具备趋药性，即趋向或逃离扩散开的化学源。Certain eukaryotic cells can swim freely in liquid environments, propelled by whiplike cilia or flagella. Both cilia and flagella have the same internal structure: nine doublets (pairs of

25、microtubules) are arranged in a ring and e*tend 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 is located. Movement is based on the activities of tiny dynein side arms tha

26、t e*tend from one of the microtubules of each doublet.*些真核细胞能在液体液体中自由运动，由纤毛或鞭毛推动。纤毛和鞭毛具有同样的部构造：九个双微管环形排列，纵向延伸，环中心是两个或以上微管组成。纤毛或鞭毛从细胞外表的基体出生长，双微管的动力蛋白臂从一侧延伸到另一侧而引起运动。Nutrients, proteins, and other materials within most plant cells are moved about via cytoplasmic streaming. The process occurs as myosi

27、n proteins attached to organelles push against microfilaments arrayed throughout the cell. Microfilaments and microtubules are responsible for almost all major cytoplasmic movements. During cell division, microtubules of the spindle assembled from tubutin subunits near organelles called centrioles m

28、ove the chromosomes.大局部植物细胞的营养，蛋白质和其它物质由细胞质流运输。这个过程是由于依附在细胞器上的肌球蛋白反推排列在细胞周围的微丝形成的。绝大局部细胞质运动由微丝和微管完成。在细胞分裂期间，中心粒周围的由微管蛋白亚基装配形成的纺锤体微管移向染色体。第二课Photosynthesis occurs only in the chlorophyll-containing cells of green plants, algae, and certain protists and bacteria.Overall, it is a process that converts

29、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.Whereas cellular respiration is highly e*ergonic and releases energy, photosynthesis requires energy and is highly endergonic.光合作用只发生

30、在含有叶绿素的绿色植物细胞，海藻，*些原生动物和细菌之中。总体来说，这是一个将光能转化成化学能，并将能量贮存在分子键中，从化学和动能学角度来看，它是细胞呼吸作用的对立面。细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过程。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 sp

31、lit (o*idized), 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 reactions, CO2 is reduced (via the addition of H atoms) to carbohydrate.These chemical events rely on the electron carrier NADPH an

32、d ATP generated by the first set of reactions.光合作用以二氧化碳和水为原材料并经历两步化学反响。第一步，称光反响，水分子分解，氧分子释放，ATP和NADPH形成。此反响需要光能的存在。第二步，称暗反响，二氧化碳被复原成碳水化合物，这步反响依赖电子载体NADPH以及第一步反响产生的ATP。Both sets of reactions take place in chloroplasts.Most of the enzymes and pigments for the lightdependent reactions are embedded in t

33、he thylakoid membrane of chloroplasts.The dark reactions take place in the stroma.两步反响都发生在叶绿体中。光反响需要的大局部酶和色素包埋在叶绿体的类囊体膜上。暗反响发生在基质中。How Light Energy Reaches Photosynthetic Cells光合细胞如何吸收光能的The energy in light photons in the visible part of the spectrum can be captured by biological molecules to do con

34、structive work.The pigment chlorophyll in plant cells absorbs photons within 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

35、 the photon boosts the energy condition of the molecule from a stable state to a less-stable e*cited state.During the light-dependent reactions of photosynthesis, as the absorbing molecule returns to the ground state, the e*cess e*citation energy is transmitted to other molecules and stored as chemi

36、cal energy.生物分子能捕获可见光谱中的光能。植物细胞中叶绿素在不同光波下吸收局部吸收光谱。在吸收分子中，光的作用使分子中的电子发生重排。光子的能量激活了分子的能量状态，使其从稳定态进入不稳定的激活态。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 ante

37、nna ple*es are present on thylakoids.Light striking any one of the 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, P

38、680 and P700, each associated with an electron acceptor molecule and 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级的叶绿素和一个或多个类胡萝卜素光合作用的辅助色素。称作天线复合体的色素分子群存在于类囊体中。激活色素分子的光能进入叶绿素反响中心，其直接参与光合作用。大局部光反响细胞器拥有两套反响中心，P680和P700，每个光系统都含有

39、一个电子受体和电子供体。这些集合体就是大家熟识的光合系统和光合系统。The Light-Dependent Reaction: Converting Solar Energy into Chemical-Bond Energy光反响：光能转化成化学键能The photosystems of the light-dependent reactions are responsible for the packaging of light energy in the chemical pounds ATP and NADPH.This packaging takes place through a

40、series of o*idation reduction reactions set in motion when light strikes the P680 reaction center in photosystem .In this initial event water molecules are cleaved, o*ygen is released, and electrons are donated.These electrons are accepted first by plastoquinone and then by a series of carriers as t

41、hey descend an electron transport chain.For each four electrons 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 ining photons boost the energy of the electrons, and they are accepted by ferredo*in.Ferredo*in is t

42、hen reo*idized, and the coenzyme NADP+ is reduced to the NADPH.The ATP generated previously and the NADPH then take part in the light independent reactions.光反响的光系统将光能转化成化学复合物ATP和NADPH。当光激活光系统的光反响中心时，通过一系列的氧化复原反响实现能量的传递。反响开场时，水被分解，氧被释放并提供电子。电子首先传递给质体醌，然后通过一系列载体形成的电子传递链。每传递4个电子，形成2个ATP。最后一个受体存在于光反响系统的

43、反响中心里。此处光子激活电子，电子传递给铁氧还蛋白。铁氧还蛋白再氧化，并且辅酶NADP+复原成NADPH。早期产生的ATP和NADPH进入暗反响。The production of ATP from the transport of electrons e*cited 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 photo

44、phosphorylation; plants also derive additional ATP through cyclic photophosphorylation, in which some electrons are shunted back through the electron transport chain between photosystems and .由电子传递链偶连产生ATP的过程称为光合磷酸化。通过光合系统流经光合系统的电子路径称非循环式光合磷酸化；植物通过循环式光合磷酸化获得额外的ATP，一些电子在光合系统和之间的电子传递链中回流。The Light-Ind

45、ependent Reactions: Building Carbohydrates暗反响：碳水化合物的形成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 fi*ed as it reacts with ribulose biphosphate (Ru

46、BP), a reaction that is catalyzed by the enzyme ribulose biphosphate carbo*ylase.The reduction Of C02 to carbohydrate (fructose diphosphate) is pleted via several more steps of the cycle.Finally, RUBP is regenerated so that the cycle may continue.由ATP和NADPH驱动的暗反响中，二氧化碳转化成碳水化合物。即卡尔文循环。二磷酸核酮糖固定二氧化碳，由二

47、磷酸核酮糖羧化酶催化。O*ygen: An Inhibitor of photosynthesis氧：光合作用的抑制因子High levels of o*ygen in plant cells can disrupt photosynthesis and can also cause photorespiration-an inefficient fun of the dark reactions in which 02 is fi*ed rather than C02 and no carbohydrate is produced.Reprieve from Photorespiration

48、: The C4 PathwayMost plants are C3 plants; they e*perience decreased carbohydrate production under hot, dry conditions as a result of the effects of photorespiration.Among C4plants, however, special leaf anatomy and a unique biochemical pathway enable the plant to thrive in and conditions.Thus C4 pl

49、ants lessen photorespiration by carrying out photosynthesis only in cells that are insulated from high levels of CO2.They also possess a novel mechanism for carbon fi*ation.大局部植物是碳3植物，在高温干旱条件下，由于光呼吸作用而使碳水化合物的合成降低。而在大多数的碳4植物中，由于叶脉的特殊构造和独特的化学路径使植物依然很茂盛。这是碳固定的一个新机制。第三课The Nucleus and ChromosomesThe cel

50、l 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 proteins, or histones, forming beadlike ple*es known as nucleos

51、omes. More coiling and supercoiling produces a dense chromosome structure. Each long strand of DNA bines with histones and nonhistone proteins to make up the substance chromatin.细胞核是贮藏遗传信息的主要场所。DNA盘绕成螺旋线以及相关的成簇蛋白质。DNA螺旋线缠绕成簇的组蛋白形成珠链状的核小体。这些螺旋和超螺旋形成致密的染色体组构造。每个长链DNA与组蛋白和非组蛋白一起构成染色质物质。A pictorial disp

52、lay of an organisms chromosomes in the coiled, condensed state is known as a karyotype.Karyotype reveal that in most cells all but se* chromosomes are present as two copies, referred to as homologous pairs.Non-se* chromosomes are called autosomes.Organisms whose cells contain two sets of parental ch

53、romosomes are called diploid; those with cells containing a single set of parental chromosomes are called haploid.染色体致密的超螺旋状态我们称染色体组。除了性染色体外，大多数细胞的染色体组成对出现，称同源染色体对。非性染色体称常染色体。生物细胞含有两套父母本染色体的称二倍体；含有单套染色体的称单倍体。The Cell CycleThe cell cycle is a regular sequence in which the cell grows, prepares for div

54、ision, 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 slow the cycle or break out of it altogether.在细胞生长过程中，细胞循环遵循特定程序，分裂

55、准备，分裂成2个子细胞，子细胞再循环。此循环使得单细胞永生。多细胞生物中的许多细胞，包括动物肌肉和神经细胞，要么降低循环速度，要么同时分裂。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;

56、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 th

57、e cell cytoplasm control the cell cycle, along with e*ternal stimulators and inhibitors such as chalones.正常细胞循环由4个时期组成。头三期包括G1,正常新代；S期,正常新代同时，DNA复制，组蛋白合成； G2 期，短期的新代和少许生长。G1, S, 和G2称分裂间期。最后是M期，有丝分裂期，复制的染色体组浓缩，移动并细胞分裂。据称是染色质控制了细胞循环，伴随外部激活因子和抑制因子如抑素。Mitosis: Partitioning the Hereditary MaterialBiologi

58、sts divide the mitotic cycle into 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 bee associated with the spindle.Eventually the chromosome

59、s bee arranged in a plane (called the metaphase plate) at a right angle to the spindle fibers.Ne*t, during anaphase, the two sister chromatids of each chromosome split, and one from each pair is drawn toward each pole of the cell.During telophase nuclear envelopes begin to form around each set of ch

60、romosomes, and division of the cytoplasm takes place.生物学家将有丝分裂划分为4个阶段。分裂前期，高度浓缩的两个染色单体通过着丝粒连接在一起。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，最后以正确的角度排列在赤道板上。在分裂后期，两个姊妹单体别离，分别拽向细胞两极。在分裂末期，在每套染色体周围形成核膜，细胞质发生分裂。As mitosis proceeds, the spindle microtubules play a crucial role in ensuring that both paired and separated

61、 chromatids move in the right directions at the proper times.Each half of the spindle forms as microtubules e*tend from each pole of a dividing cell to the region of the metaphase plate.During prophase, other microtubules, the centromeric fibers, e*tend outward from the spindle poles to structures o

62、n the chromosomes called kinetochores.During anaphase the fibers begin to shorten, and the chromatids begin to move apart.在有丝分裂过程中，是纺锤体微管确保了染色单体在适当时间以正确方向进展别离。纺锤体微管由两极向赤道板延伸。在分裂前期，其它微管，着丝粒纤维延伸到染色体的动粒。在分裂后期，纤维开场变短，染色单体别离。The spindle forms differently in plant and animal cells.In animals it is associa

63、ted with centriole, while in plant and fungal cells spindle formation is associated with reions called microtubule organizing centers.植物和动物细胞形成的纺锤体不同。动物细胞与中心粒相连，而在植物和真菌细胞中，纺锤体与微管组织中心的离子相连。Cytokinesis: Partitioning the Cytoplasm胞质分裂：细胞质别离The division of the cell cytoplasm at the end of mitosis is cal

64、led cytokinesis.In animal cells it takes place as a ring of actin filaments contracts around the cell equator, pinching the cell in two.In 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.Cell wall material i

65、s then deposited in the region of the cell plate.在动物细胞中，环形肌动蛋白丝延赤道板收缩而使细胞一分为二。在植物细胞中，在赤道板形成新的细胞板。Meiosis: The Basis of Se*ual ReproductionMeiosis is a special form of cell division that takes place in the reproductive organs that produce se* cells.Like mitosis, it takes place after DNA replication has occurred and involves two sequential nuclear divisions (meiosis I and meiosis ).These divisions result in four daughter cells, each with half th