1、Lesson OneLesson OneInside the Living Cell: Structure andFunction of Internal Cell Parts1、 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 cellconsists of this semifluid substance, which is bounde
2、d on the outside by the plasma membrane. Organelles aresuspended within it, supported by the filamentous network of the cytoskeleton. Dissolved in the cytoplasmic fluidare nutrients, ions, soluble proteins, and other materials needed for cell functioning.生命的大部分特征表现在细胞质的特征上。细胞质大部分由半流体物质组成，并由细胞膜（原生质膜）
3、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。2、The Nucleus: Information Central（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 cont
4、ains one or two organelles-the nucleoli-that play a role in cell division. A pore-perforated sac called the nuclear envelope separates thenucleus and its contents from the cytoplasm. Small molecules can pass through the nuclear envelope, but largermolecules such as mRNA and ribosomes must enter and
5、exit 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，小分子可以自由 核膜， mRNA 核 体 大分子 核孔 。3、Organelles: Specialized Work Units（细胞器：特 的 ）All eukaryotic cells contain most of the various kinds of organelles, and each organelle performs a specializedfunction in the ce
6、ll. Organelles described in this section include ribosomes, the endoplasmic reticulum, the Golgicomplex, vacuoles, lysosomes, mitochondria, and the plastids of plant cells.有的真核细胞 含有多 细胞器， 个细胞器 有其特 。 核 体， 质 ， 体 ，溶体，体 物细胞中的质体。The number of ribosomes within a cell may range from a few hundred to many t
7、housands. This quantityreflects the fact that, ribosomes are the sites at which amino acids are assembled into proteins for export or for usein cell processes. A complete ribosome is composed of one larger and one smaller subunit. During protein1Lesson Onesynthesis the two subunits move along a stra
8、nd of mRNA, “reading“ the genetic sequence coded in it andtranslating that sequence into protein. Several ribosomes may become attached to a single mRNA strand; such acombination is called a polysome. Most cellular proteins are manufactured on ribosomes in the cytoplasm.Exportable proteins and membr
9、ane proteins are usually made in association with the endoplasmic reticulum.核 体的量currency1“fi，核 体是fl 组成蛋白质的 。 的核 体由大 小 组成。核 体mRNA动并”遗传， 成蛋白质。一 mRNA上可 有多个核 体，多核 体。大多细胞蛋白是由细胞质中核 体生。 蛋白 膜蛋白 质 有。The endoplasmic reticulum, a lacy array of membranous sacs, tubules, and vesicles, may be either rough (RER)o
10、r smooth (SER). Both types play roles in the synthesis and transport of proteins. The RER, which is studdedwith polysomes, also seems to be the source of the nuclear envelope after a cell divides.质 ，有 的生物，有 状，状分，以及 。 蛋白质的 成 有。 质 上分 许多核 体， 可 细胞分裂 需的细胞膜。SER lacks polysomes; it is active in the synthes
11、is of fats and steroids and in the oxidation of toxic substances inthe cell. Both types of endoplasmic reticulum serve as compartments within the cell where specific products canbe isolated and subsequently shunted to particular areas in or outside the cell. 质 上 核 体， 作用是 的 成以及细胞 有 物质的。 质 成的物在其中进 分流或
12、 细胞 。Transport vesicles may carry exportable molecules from the endoplasmic reticulum to another membranousorganelle, the Golgi complex. Within the Golgi complex molecules are modified and packaged for export out ofthe cell or for delivery else where in the cytoplasm.小 可 分子“ 质 体上。在 体中，包 细胞或传细胞质中的其 。
13、Vacuoles in cells appear to be hollow sacs but are actually filled with fluid and soluble molecules. The mostprominent vacuoles appear in plant cells and serve as water reservoirs and storage sites for sugars and othermolecules. Vacuoles in animal cells carry out phagocytosis (the intake of particul
14、ate matter) and pinocytosis(vacuolar drinking).细胞中的 是中 的， 上 了体 可溶分子。最 的存在于物细胞中， ， 以及其它分子。动物中的 胞 作用。 A subset of vacuoles are the organelles known as lysosomes, which contain digestive enzymes (packaged inlysosomes in the Golgi complex) that can break down most biological macromolecules. They act to
15、digest food2Lesson Oneparticles and to degrade damaged cell parts.溶体是 ，含有 ， 解大部分生物大分子。 物微 解损伤的细胞残片。Mitochondria are the sites of energy-yielding chemical reactions in all cells. In addition, plant cells containplastids that utilize light energy to manufacture carbohydrates in the process of photosyn
16、thesis. It is on the largesurface 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.体是细胞中学 的 。另 ，物细胞中的质体在 作用中利用 生碳 物，体 嵴上 了很大的表 积并分
17、 ATP。体自我制，并且可 是自由生活的原核生物在进中形成的 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 phot
18、osynthesis. The internal structure of chloroplasts includesstacks of membranes called grana, which are embedded in a matrix called the stroma.质体有 ：白色体，缺乏色素，是淀粉，蛋白质 油的 ；色质体，含有色素。叶绿体是最 的色质体，含有 作用有的叶绿素。叶绿体的 部结构是由多层膜形成的叶绿体 ，其中包埋在 质中的 子座。4、The Cytoskeleton（细胞骨架）All eukaryotic cells have a cytoskeleton, w
19、hich is a convoluted latticework of filaments and tubules thatappears to fill all available space in the cell and provides support for various other organelles. A large portion ofthe cytoskeleton consists of threadlike microfilaments composed mainly of the contractile protein actin. They areinvolved
20、 in many types of intracellular movements in plant and animal cells. A second protein, myosin, is involvein the contraction of muscle cells. Another main structural component of the cytoskeleton consists ofmicrotubules, which are composed of the globular protein tubulin and together act as scaffoldi
21、ng that provides astable 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 togenerate forces that cause movements.有的细胞 有细胞骨架， 络结构的纤丝 了它 触及的全部
22、间并且对细胞器 支持作用。细胞骨架大部分由微丝组成，微丝 由可收缩的肌动蛋白组成。动物细胞的许多 细胞 动肌动蛋白有。第二 蛋白是肌球蛋白，它肌肉细胞的收缩有。细胞骨架的另一个 结构成分是微3Lesson One，由球状的微 蛋白组成， 脚手架一般维持细胞的稳 形态。细胞骨架的中间丝 了细胞质伸缩动力。机械，例如，肌球蛋白，动力蛋白，驱动蛋白微丝，微 相互作用生动力 引细胞 动。5、Cellular Movements（细胞 动）Although the cytoskeleton provides some stability稳 to cells, its microtubules and f
23、ilaments 丝状物 and theirassociated proteins enable cells to move by creeping 爬 or gliding 动. Such movements require a solid 体的 substrate to which the cell can adhere附 and can be guided by the geometry何形状of the surface. Somecells also exhibit 展览 chemotaxis,趋药性 the ability to move toward or away from th
24、e source of a diffusing 扩散chemical.尽 细胞骨架 了细胞的某些稳 性，微丝，微 及相蛋白 使细胞爬 或动。这 动需 体 质依托并 表 何形状的改currency1 动。某些细胞具 趋药性，即趋向或逃离扩散开的学源。Certain eukaryotic cells can swim freely in liquid environments, propelled by whiplike cilia纤毛or flagella鞭毛. Both cilia and flagella have the same internal structure: nine doub
25、lets (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 体is located. Movement is based on the activities of tiny dyne
26、in动力蛋白 side arms that extend from one of the microtubules of each doublet成对的东西.某些真核细胞 在体体中自由 动，由纤毛或鞭毛推动。纤毛 鞭毛具有同样的 部结构：九个双微 环形排列，纵向延伸，环中心是 个或以上微 组成。纤毛或鞭毛“细胞表 的 体生长，双微 的动力蛋白臂“一侧延伸另一侧 引 动。Nutrients, proteins, and other materials within most plant cells are moved about via cytoplasmic streaming. The pr
27、ocess occurs as myosin肌凝蛋白 proteins attached to organelles 细胞器,小器官 push against microfilaments arrayed 展示throughout the cell. Microfilaments and microtubules are responsible for almost all major cytoplasmic movements. During cell division, microtubules of the spindle assembled 集 , 收集 from tubutin su
28、bunits near organelles called centrioles move the chromosomes.大部分物细胞的营养，蛋白质 其它物质由细胞质流 。这个 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。绝大部分细胞质 动由微丝 微 成。在细胞分裂期间，中心周围的由微 蛋白 配形成的纺锤体微 向染色体。Lesson TwoPhotosynthesisPhotosynthesis occurs only in the chlorophyllchlorophyll叶绿素-containing cells of green plants, algae藻, an
29、d4Lesson Onecertain protists 原生生物and bacteria. Overall, it is a process that converts light energy into chemical energy thatis stored in the molecular bonds. From the point of view of chemistry and energetics, it is the opposite of cellularrespiration. Whereas 然 cellular细胞的 respiration 呼吸is highly e
30、xergonic吸收 量的 and releases energy,photosynthesis 作用 requires energy and is highly endergonic. 作用只发生在含有叶绿素的绿色物细胞，海藻，某些原生动物 细菌中。总体来说，这是一个 转成学 ，并 量贮存在分子键中，“学 动 学角度来 ，它是细胞呼吸作用的对 。细胞呼吸作用是 度 的， 作用是需 量并 吸 的 程。Photosynthesis starts with CO2 and H2O as raw materials and proceeds through two sets of partial r
31、eactions. Inthe first set, called the light-dependent reactions, water molecules are split裂开 (oxidized), 02 is released, and ATPand NADPH are formed. These reactions must take place in the presence of 在 light energy. In the secondset, called light-independent reactions, CO2 is reduced (via the addit
32、ion of H atoms) to carbohydrate. Thesechemical events rely on the electron carrier NADPH and ATP generated by the first set of reactions. 作用以二碳 原 并 学反 。第一 ，反 ，分子分解，分子 ，ATP NADPH形成。 反 需 的存在。第二 ， 反 ，二碳被 原成碳 物，这反 依 子 体NADPH以及第一 反 生的ATP。Both sets of reactions take place in chloroplasts. Most of the enzy
33、mes and pigments 色素for thelightdependent reactions are embedded 的 含的in the thylakoid 体 membrane膜 膜 of chloroplasts叶绿体. The dark reactions take place in the stroma. 质反 发生在叶绿体中。反 需 的大部分 色素包埋在叶绿体的 体膜上。 反 发生在 质中。1、How Light Energy Reaches Photosynthetic Cells（ 细胞如何吸收 的）The energy in light photons in the
34、 visible part of the spectrum can be captured by biological molecules to doconstructive work. The pigment chlorophyll in plant cells absorbs photons within a particular absorptionspectrums statement of the amount of light absorbed by chlorophyll at different wavelengths. When light isabsorbed it alt
35、ers the arrangement of electrons in the absorbing molecule. The added energy of the photon booststhe energy condition of the molecule from a stable state to a less-stable excited state. During the light-dependentreactions of photosynthesis, as the absorbing molecule returns to the ground state, the
36、“excess“ excitation energyis transmitted to other molecules and stored as chemical energy.生物分子 可 中的 。物细胞中叶绿素在 同 吸收部分吸收 。在吸收分子中，的作用使分子中的 子发生排。子的 量 活了分子的 量状态，使其“稳 态进 稳 的5Lesson One活态。All photosynthetic organisms contain various classes of chlorophylls and one or more carotenoid (accessory)pigments tha
37、t also contribute to photosynthesis. Groups of pigment molecules called antenna complexes arepresent on thylakoids. Light striking any one of the pigment molecules is funneled to a special chlorophyll amolecule, termed a reaction-center chlorophyll, which directly participates in photosynthesis. Mos
38、tphotosynthetic organisms possess two types of reaction-center chlorophylls, P680 and P700, each associated withan electron acceptor molecule and an electron donor. These aggregations are known respectively as photosystem(P700) and photosystem (P680).有的 作用生物含有 同 的叶绿素 一个或多个 素（ 作用的色素）。作 体的色素分子存在于 体中。
39、活色素分子的 进 叶绿素反 中心，其currency1 作用。大部分反 细胞器“有 反 中心，P680 P700， 个 含有一个 子体 子 体。这些集 体fi是大fl 的 。2、The Light-Dependent Reaction: Converting Solar Energy into Chemical-Bond Energy反 ： 转成学键 The photosystems of the light-dependent reactions are responsible for the packaging of light energy in thechemical compound
40、s ATP and NADPH. This packaging takes place through a series of oxidation reductionreactions set in motion when light strikes the P680 reaction center in photosystem . In this initial event watermolecules are cleaved, oxygen is released, and electrons are donated. These electrons are accepted first
41、byplastoquinone and then by a series of carriers as they descend an electron transport chain. For each four electronsthat pass down the chain, two ATPs are formed. The last acceptor in the chain is the P700 reaction center ofphotosystem . At this point incoming photons boost the energy of the electr
42、ons, and they are accepted byferredoxin. Ferredoxin is then reoxidized, and the coenzyme NADP+ is reduced to the NADPH. The ATPgenerated previously and the NADPH then take part in the light independent reactions.反 的 转成学 物ATP NADPH。 活 的反 中心， 一 列的 原反 现 量的传。反 开，被分解，被 并 子。 子 传质体，然 一 列 体形成的 子传。 传4个 子，形成2
43、个ATP。最 一个体存在于反 的反 中心”。 子 活 子， 子传 蛋白。 蛋白，并且NADP 原成 P。期生的 P P进 反 。The production of ATP from the transport of electrons excited by light energy down an electron transport chainis termed photophosphorylation. The one-way flow of electrons through photosystems II and I is called noncyclic6Lesson Onephot
44、ophosphorylation; plants also derive additional ATP through cyclic photophosphorylation, in which someelectrons are shunted back through the electron transport chain between photosystems and .由 子传生ATP的 程 。 流 的 子 环 ；物 环 的 P，一些 子在 间的 子传中流。3、The Light-Independent Reactions: Building Carbohydrates 反 ：碳
45、物的形成In the light-independent reactions of photosynthesis, which are driven by ATP and NADPH, C02 is converted tocarbohydrate. The reactions are also known as the Calvin-Benson cycle. Atmospheric CO2, is fixed as it reactswith ribulose biphosphate (RuBP), a reaction that is catalyzed by the enzyme ri
46、bulose 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 NADPH驱动的 反 中，二碳转成碳 物。即 环。二 核 二碳，由二 核 。4、Oxygen: An Inhibitor of photosynthesis（： 作用的 制 子）High l
47、evels of oxygen in plant cells can disrupt photosynthesis and can also cause photorespiration-aninefficient fun of the dark reactions in which 02 is fixed rather than C02 and no carbohydrate is produced.5、Reprieve from Photorespiration: The C4 PathwayMost plants are C3 plants; they experience decrea
48、sed carbohydrate production under hot, dry conditions as aresult of the effects of photorespiration. Among C4 plants, however, special leaf anatomy and a uniquebiochemical pathway enable the plant to thrive in and conditions. Thus C4 plants lessen photorespiration bycarrying out photosynthesis only in cells that are insulated from high levels of CO2. They also possess a novelmechanism for carbon fixation.大部分物是碳 物，在 ，由于呼吸作用 使碳 物的 成 。 在大多的碳 物中，由于叶 的特 构 特的学 使物依然很 。这是碳 的一个机制。Lesson ThreeCellular Repro
