Lesson One
Inside the Living Cell: Structure and
Function of Internal Cell Parts
细胞的内部结构及其功能
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 semi-fluid substance, which is bounded on the outside 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）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（细胞核：信息中心）
The eu-karyotic cell nucleus is the largest organelle and houses the genetic material (DNA) on chromosomes. degrade(In pro-karyotes 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 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.
真核细胞的细胞核是最大的细胞器，在细胞核内的染体上储存着遗传物质DNA（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 pe
rforms a specialized function in the 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，内质网，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 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 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 proteins and membrane proteins are usually made in association with the endoplasmic reticulum.
细胞内的核糖体数量变化从几百到几千。（这个数据反映了一个事实，即）核糖体是氨基酸组装成蛋白质的重要场所。完整的核糖体由大亚基和小亚基组成。（在蛋白质合成过程中，）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内质网有关。
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 RER, which is studded with polysomes, also seems to be the source of the nuclear envelope after a cell divides.
（内质网，由一系列管状泡状的囊膜排列成花边结构，）由一系列管状泡状的囊膜排列成花边结构的内质网，可分为粗面内质网（RER）和滑面内质网（SER）。两种都与蛋白质的合成和运输有关。粗糙内质网上分布许多聚核糖体，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 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）滑面内质网上无核糖体，主要作用是脂肪和类固醇的合成以及细胞内有毒物质的氧化。在细胞内，两种内质网形成各自独立的空间，分别进行特定产物的合成，并将产物分流或运输到细胞外。
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.
运输小泡能够将可运输分子从内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 hollow sacs but are actually filled with fluid and soluble mo
lecules.  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 (vacuolar drinking).
细胞中的液泡好象（貌似？）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，储备水，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 is 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.
溶酶体是液泡亚单位，含有消化酶，(打包在高尔基体复合体的溶酶体可)降解大部分生物大分子。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 pr
ocess 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 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。线粒体的内嵴为ATP（三磷酸腺苷酶）的分布提供了很大的表面。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。

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