Inside the LivingCell: StructureandFunctionof Internal Cell PartsCytoplasm: The Dynamic, MobileFactory细胞质:动力工厂Most of the propertieswe associatewithlife areproperties of the cytoplasm.Much of the mass of a cell consistsof this semifluid substance, whichisbounded on theoutside bythe plasmamembrane.Organelles are suspended within it,supported by the filamentous network ofthe cytoskeleton. Dissolvedin thecyt oplasmic fluidare nutrients,ions,solubleproteins, an dothermaterials 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)Theeukaryotic cell nucleus isthelargest organelle andhousesthe geneticmaterial (DNA) onchromosomes.(In prokaryotes the hereditarymaterial isfound in the nucleoid.)Thenucleusalso contains o ne or two organelles-thenucleoli-thatplay arole in c elldivision.A pore-perforated sac called thenuclear envelope separates the nucleus and itscontentsf rom the cytoplasm.Small moleculescan passthro ugh the nuclear envelope,but largermolecules such as mRNAand ribosomes must enter and 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 containmost of the various kinds of organelles, andeach organelle performs a specialized function in the cell. Organellesdescribed in thissecti onincluderibosomes, the endoplasmic reticulum,the Golgi complex,vacuoles, lysosomes, mitochondria, and the plastidsof 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 afew hundred to manythousands. This quantity reflect sthe fact that,ribosomes are the sitesat which amino acidsare assembled into proteinsfor export or for use in cell processes. A complete ribosome is composed of one larger andone smaller subunit. During protein synthesis the two subunits move along a strand of mRNA,"reading"the genetic sequence codedin it and translating that sequence into protein. Several ribosomesmaybecome attachedtoasingle mRNAstrand;such a combinationis called a polysome. Most cellularproteins are manufactured on ribosomesin the cytoplasm.Exportable proteins and membraneproteins are usuallymade inassociation with theendoplasmic 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内质网有关。
The endoplasmic reticulum, a lacyarray of membranous sacs, tubules,and vesicles, maybe either rough(RER) or smooth (SER).Both typesplay roles in the synthesisandtransport of proteins.The RER, which isstudded withpolysomes,also seems to be the source of thenuclear envelope after a cell divides.内质网,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。
粗糙内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 lackspolysomes; it is activeinthe synthesis o ffatsand steroids andin theoxidation of toxicsub stances in thecell.Both types of endoplasmic reticulumserve as compartments within the cell wherespecificproducts can be isolated and subsequently shunted toparticular areasin or outsidethe cell.光滑内质网上无核糖体,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。
两种内质网合成的产物在其中进行分流或运输到细胞外。
Transportvesicles maycarry exportable mole culesfromthe endoplasmic reticulum toanother membranousorganelle, theGolgi complex.Withinth eGolgi complex molecules are modified andpackaged for exportout ofthe cell or for delivery else wherein thecytoplasm.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。
Vacuolesin cellsappeartobe hollow sacs but are actually filled with fluid andsoluble molecules. T he mostprominentvacuolesappearin plantce lls and serve as water reservoirs andstoragesitesfor sugars and other molecules. Vacuolesin anima lcells carry out phagocytosis (the intakeof particulat ematter) andpinocytosis(vacuolar 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,储备水,糖以及其它分子。
动物中的液泡起吞噬和胞饮作用。
Asubset ofvacuolesare the organelles knownaslysosomes, which contain digestiveenzymes (packaged in lysosomes in theGolgi complex) that can breakdown most biological macromolecules. They act todigestfood particles andtodegrade damaged cellparts.溶酶体是液泡亚单位,含有消化酶,降解大部分生物大分子。
消化食物微粒和降解损伤的细胞残片。
Mitochondria are the sites ofenergy-yielding chemical reactions in all cells.In addition, plant cellscontain plastids that utilizelight energy to manufacture carbohydrates in theprocess ofphotosynthesis. It is on the large surface area provided by the i nnercristae ofmitochondriathat ATP-generatingenzymes are located. Mitochondriaare self-replicatin g, andprobably theyare theevolutionary descendantsof what wereoncefree-livingprokaryotes.线粒体是细胞中化学产能的场所。