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1、CHARPTER 4,细胞环境与互作 Interactions Between Cells and Their Environment,OUTLINE,4.1 CELL SURFACE 4.2 CELL ENVIRONMENT 4.3 CELL RECOGNIZATION 4.4 CELL JUNCTION,An overview of cells interact with their environment,4.1 Cell Surface,在结构上，包括： 细胞被(cell coat) 细胞质膜 表层胞质溶胶(corticol cytosol),在功能上： 保护细胞,使细胞有一个相对稳定
2、的内环境； 参与细胞内外的物质交换和能量交换； 参与信号的识别和信息的传递； 参与细胞运动； 维护细胞的各种形态； 与免疫、癌变等有十分密切关系。,表层胞质溶胶(cytosol)： 其中含有高浓度的蛋白质,其厚度在哺乳类细胞为0.1-0.2m,其中没有核糖体和线粒体, 但是有较多的微丝和微管,它们对于维持细胞的形态和运动具有重要作用。,细胞被 Glycocalyx) 组成： 由细胞表面的碳水化合物形成的质膜保护层，又称为多糖包被。 功能： The glycocalyx is thought to mediate cell-cell and cell-substratum interaction
3、s, provide mechanical protection to cells, and serve as a barrier to particles moving toward the plasma membrane.,电镜下的细胞表面,细胞表面结构,4.1.2 PLANT CELL WALLS,植物细胞壁的作用 提供机械强度 保护细胞免遭渗透及机械损伤 植物细胞壁是一个动态结构，能够进行很多活动: 与细胞壁有关的酶能够吸收细胞外的营养，生成能够通过细胞膜进入细胞的小分子化合物。 细胞壁也可以作为物质通透的障碍，在代谢和分泌过程中起重要作用。,细胞壁的结构组成 植物的细胞壁相当于动物细
4、胞的细胞 外基质(!)： 动物细胞的细胞外基质的主要成分是 蛋白质分子； 植物的细胞壁主要是多糖，其中最主 要的是纤维素。 植物细胞壁的骨架：纤维素,植物细胞壁的骨架：纤维素 Cellulose molecules are organized into microfibrils that confer rigidity to the cell wall and provide resistance to tensile (pulling) forces. ? Each microfibril is 5-10 nm in diameter and is composed of bundles o
5、f 30 to 60 cellulose molecules oriented parallel to one another and held together by hydrogen bonds. ?,植物细胞壁中的纤维素,？,The matrix of the plant cell walls,Hemicellulose Hemicelluloses are branched polysaccharides whose backbone consists of one sugar, such as glucose, and side chains of other sugars, suc
6、h as xylose. Hemicellulose molecules bind to the surfaces of cellulose microfibrils, cross-linking them into a complex structural network.,Pectins： Pectins are a heterogeneous class of negatively charged polysaccharides containing galacturonic acid（半乳糖醛酸）； Like the glycosaminoglycans of animal cell
7、matrices, pectins hold water and thus form an extensive hydrated gel（水合胶）that fills in the spaces between the fibrous elements； When a plant is attacked by pathogens, fragments of pectins released from the wall trigger a defensive response by the plant cell； Purified pectin is used commercially to p
8、rovide the gel-like consistency of jams and jellies.,Structure Proteins: Structure Protein functions are not well understood. One class, the extensins, provide structural support and may form a barrier to invading microorganisms.,植物细胞壁的分泌合成,中间层形成： 主要是果胶。果胶是相邻两细胞壁所共有，并且具有将两个细胞连接在一起的作用。 初生壁形成： 是细胞正在生长
9、时形成的。初生壁的厚度为100-200nm,与动物细胞的基膜相当。初生壁由纤维素、半纤维素、果胶和糖蛋白等松散组成。 次生壁形成： 是在细胞停止生长后分泌形成的。主要是增加细胞壁的厚度和强度。次生壁主要在初生壁的内层。,PLANT CELL WALLS,19,4.2 Extracellular matrix,Many types of animal cells are surrounded by an extracellular matrix (ECM)-an organized network of extracellular materials that is present beyond
10、 the immediate vicinity of the plasma membrane. The ECM is more than an inert packing material, it often plays a key regulatory role in determining the shape and activities of the cell . 能够分泌和形成细胞外基质的主要细胞类群是成纤维细胞(fibroblast)和其他特化组织的细胞。,20,For example: Enzymatic digestion of the ECM that surrounds cu
11、ltured cartilage(软骨） cells or mammary gland epithelial cells causes a marked decrease in the synthetic and secretory activities of the cells. Addition of extracellular matrix materials back to the culture dish restores the differentiated state of the cells and their ability to produce their usual ce
12、ll products.,21,Typical Extracellular matrix,22,细胞外基质的组成可分为三大类 蛋白聚糖(proteoglycan) 结构蛋白 如胶原和弹性蛋白，它们赋予基质一定的强度和韧性。 黏着蛋白(adhesive proteins) 如纤连蛋白和层粘蛋白，它们促使细胞同基质结合。,23,4.2.1 细胞外基质的基础物质,蛋白聚糖(Proteoglycan,PG) 结构与功能 Protein-polysaccharide complex is called a proteoglycan A proteoglycan consists of a core pr
13、otein molecule to which chains of glycosaminoglycans (GAGs,糖胺聚糖) are covalently attached. Because of the negative charges borne on the sulfated GAGs, proteoglycans bind huge numbers of cations, which in turn bind large numbers of water molecules. As a result, proteoglycans form a porous, hydrated ge
14、l that fills the extracellular space like packing material and resists crushing (compression) forces.,24,Proteoglycan,25, Glycosaminoglycans Each glycosaminoglycan chain is composed of a repeating disaccharide; that is, it has the structure -A-B-A-B-A-, where A and B represent two different sugars.
15、GAGs are highly acidic due to the presence of both sulfate and carboxyl groups attached to the sugar rings. 糖胺聚糖的二糖单位之一是氨基己糖(氨基葡萄糖或氨基半乳糖), 故称为糖胺聚糖。 糖胺聚糖包括 硫酸软骨素(chondroitin sulfate) 透明质酸(hyaluronic acid)等。,26,构成糖胺聚糖的二糖,27,透明质酸(hyaluronic acid) 细胞外基质中发现的大多数糖胺聚糖 都是作为蛋白聚糖的一个成分而存在， 惟一例外的是透明质酸，它在细胞外 基质中也
16、可游离存在。 透明质酸在结缔组织中起强化、弹性和润滑作用,具有抗压能力。,28,4.2.2 结构蛋白,胶原(Collagen) 基本特性： Collagen is a family of fibrous glycoproteins that are present only in extracellular matrices. Collagen is the single most abundant protein in the human body (constituting more than 25 percent of all protein), Collagens are found throughout the animal kingdom and are noted for their high tensile strength, that is, their resistance to pulling for
