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Structure and Function of Inter Cell Parts

(2010-06-21 17:05:45)

Inside the Living Cell: Structure and Function of Inter Cell Parts

活细胞内部:细胞内部的结构和功能

1.   Cytoplasm:The Dynamic Mobile

细胞质:动力、移动工厂

Most of the properities we associate with life are properities of the cytoplasm . Much of the mass of a cell consists of this semifuluid substance, which is bounded on the outside by the plasma membrance. Organelles are suspended within it , supported by the filamentous network of the cytoskeleton. Dessolved in the cytoplasmic fluid are nutrients, ions , soluble proteins, and other materials needed for cell functioning.

生命的大部分特征都就是细胞质的特征。细胞的许多物质都是由这种半流体组成的,外部由质膜包裹。细胞器悬浮其中,并由细胞骨架的细丝网状结构支撑着。溶解在细胞质中的物质有营养物质、离子、可溶性蛋白、以及其它细胞功能所需的原料。

2.  The Nucleus: Information Central

细胞核:信息中心

The eukaryotic cell nucleus is the largest organelle and houses the geneticmaterial(DNA) on chromosome. (In prokaryotes athe hereditary material is found in the nucleoid.)The nucleus also contains one or two organelles-the nuleoli-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细胞中最大的细胞器,在染色体上储存着遗传物质(DNA)。(原核细胞的遗传物质则存在于拟核上)。细胞核还拥有一个或两个细胞器—核仁—在细胞分裂中起作用。被称作核膜的多孔囊将细胞核与细胞质隔开。小分子可以通过核膜,但是大分子物质像mRNA和核糖体则需要通过核孔进出。

3.   Organelles: Specialized Work Units

细胞器:特定的工作单元

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 Golgi complex, vacuoles, lysosomes, mitochondria, and the plastids of plant cells.

真核细胞含有各种各样的细胞器,每一个细胞器都在细胞中起着特定的作用。这一部分介绍到的细胞器有核糖体、内质网、高尔基复合体、液泡、溶酶体、线粒体、和植物细胞质体。

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 process. 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 tanslating 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.

细胞内染色体的数目从几百到几千不等。其数量表明了核糖体是细胞过程中将氨基酸组装成蛋白质输出或供细胞所用的场所。一个完整的核糖体是由一个较大的大亚基和一个较小的小亚基组成。在蛋白质合成过程中,两个亚基沿着一条mRNA移动,“阅读”着编码在其中的遗传序列,并将遗传序列翻译成蛋白质。几个核糖体逐步附着到一条单链mRNA上,这样的组合被称为多聚核糖体。大多数细胞蛋白质都是在细胞质中的核糖体上被制造的。可输出蛋白和膜蛋白的制造通常与内质网有关。

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. SER lacks polysomes; it is active in the synthesis of fats and steroids and in the oxidation of toxic subtances in the cell. Both types of endoplasmic reticulum serve as compartments wihiin the cell where specific products can be isolated and subsequently shunted to particular areas in or outside the cell.

内质网,是一些不规则排列的膜囊,小管,和液泡组成的。分为糙面型内质网和滑面型两种。它们都在蛋白合成与运输中起作用。糙面型内质网,镶嵌在多聚核糖体中,可能是细胞分裂后核膜的来源。滑面型内质网不含多聚核糖体,积极参与脂肪和类固醇的合成以及细胞中有毒的亚物质的氧化。这两种内质网在细胞中作为分室,使特定产品分隔开,随后将他们转移到细胞内外特定的部分或细胞外。

Transport vesicles may carry exportable molecules from the endoplasmic reticulum to another membranous organelle, the Golgi complex. Whithin the Golgi complex molecules are modified and packaged for export out of the cell or for delivery else where in the cytoplasm.

运输液泡能够将可输出分子从内质网运送到其他的膜细胞器上-高尔基复合体。在高尔基复合体内,分子被组装修改并运送出细胞或者细胞质中的其他部分。

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 cells carry out phagocytosis (the intake of particulate matter )and pinocytosis (vacuolar drinking )

细胞中的液泡是中空的囊状结构,里面充满着液体和可溶性分子。植物细胞内最主要的液泡起着储藏水分,糖类以及其他分子的作用。动物细胞中的液泡则主要起吞噬作用(摄入微粒物质)和胞饮作用(通过液泡饮入)。

A subset of vacuoles is the organelles known as lysosomes, which contain digestive enzymes (packaged in lysosome in the Golgi complex )that can break down most biological macromolecules. They act to digest food particles and to degrade damaged cell parts.

一小部分的液泡分子组成的细胞器被称为溶酶体,它包含消化酶(在高尔基复合体中的溶酶体上组装完成),能够分解大多数生物微分子。溶酶体充当着消化食物微粒和降解受损的细胞部分。

Mitochodria 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-generating enzymes are located. Mitochondria are self-replicating, and probably they are the evolutionary descendants of what were once free-living prokaryotes.

线粒体是所有细胞中化学反应和产能场所。除此之外,植物细胞包含着在光合作用中利用光能产生二氧化碳的质体。ATP产生酶存在于线粒体上内质体的巨大表面上。线粒体可以自我复制,很有可能是曾经游离原核生物演化而来的后代。

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 chorophyll used in photosythesis. The internal structure of chloroplasts includes stacks of membranes called grana, which are embedded ,in a matrix called the stroma.

质体分为两种:一种是白色体,不含色素,作为淀粉,蛋白质,脂类的贮藏场所;另一种是有色体,包含色素。最重要的色素细胞是叶绿体-包含光合作用中所需的叶绿素。叶绿体的内部结构包括称为极粒的堆叠的薄膜,极粒包埋在称为基质的细胞间质中。

4.       The Cytoskeleton

All eukaryotic cells have a ytoskeleton, which is a convoluted latticework of filaments and tubules that apears to fill all available space in the cell and provides support for various other organelles. A large portion of the cytoskeleton consists of threadlike icrofilaments composed mainly of the contractile protein actin. They are involed of intracellular movements in plant and animal cells. A second protein , myosin , is involve in the contraction of the globular protein tubulin and of the cytoskeleton consists of microtubules, which are composed of the globulr protein tubulin and together act as scaffolding that provides a stable cellshape. Cyotoskeletal intermediate filaments appear to impart tensile strength to the cell cytoplasm. Mechanoenzymes such as yosin, dynein, and kinesin interact with the cytoskeletal filaments and tubules to generate forces that cause movements.

  细胞骨架

所有的原核细胞都含有一个细胞骨架,细胞骨架是纤丝和细管缠绕在一起的格子结构。似乎充满着细胞中所有可利用的空间,  为各种各样的其他细胞提供支持。细胞骨架的大部分主要是由可收缩的蛋白肌动蛋白组成的细长的微丝。细胞骨架的另一个主要结构成分是由球状蛋白微管蛋白组成组很的微管,并一起作用作为支架提供一个稳定的细胞形态。细胞骨架的中间丝为细胞质传递张力。像肌球蛋白,动力蛋白和驱动蛋白这样的机械酶,与细胞骨架纤丝和细管作用产生动力,引起细胞运动。

5.       Cellular Movements

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 be guided by the geomery of the surface. Some cells also exhibit chemotaxis, the ability to move toward or away from the source of a diffusing chemical.

  细胞运动

虽然细胞骨架为细胞提供了稳定性,它的微管和细丝以及相关的蛋白石细胞能够通过爬行和滑动运动。这些运动需要能够依附的固体基质和表面几何形状的的引导。一些细胞还表现出趋化性,可以趋向和远离扩散的化学源。

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 microtubules) are arranged in a ring and extend the length of the cilum or flagellum, and two more imcrotubules run down the center of the ring. Every cilium or flagellun grows 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.

某些原核细胞能够在液体环境中自由游动,由鞭子似的纤毛和鞭毛推进。鞭毛和纤毛都有相同的内部结构:九对(微管对)排列在一个环上,鞭毛和纤毛伸展着长度,两个以上的微管沿着环的中心向下运动。每一个纤毛和鞭毛只从基体位于的细胞表面生长出来。运动是基于肌动蛋白侧臂的活动,从其中的一个微管延伸到每一对上。

Nutrients, 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. Microsfilaments and microtubules are responsible for almost all major cytoplasmic movements. During cell division, microbubules of the spindle-assembled form tubulin subunits near organelles called centrioles-move the chromosomes.

大多数植物细胞内的营养物质,蛋白质,其他的原料都是通过细胞质的流动而移动的。这个过程发生,当肌球蛋白附着在细胞器上,由细胞细胞上排列的微丝推动的时候。微丝和微管主要负责大多数细胞质移动。在细胞分裂中,仿锤体的微管-从靠近称为中心体的细胞器的微管蛋白装配-使染色体移动。

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