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1、Cell Membrane and Cell Surface,I. Cell Membrane II. Cell Junctions III. Cell Adhesion IV. Extracellular Matrix,http:/ Biomembranes: Their Structure, Chemistry and Functions,Learning objectives: A brief history of studies on the structrure of the plasma membrane Model of membrane structure: an experi
2、mental perspective The chemical composition of membranes Characteristics of biomembrane An overview of the functions of biomembranes,1. A brief history of studies on the structrure of the plasmic membrane,A. Conception: Plasma membrane(cell membrane), Intracellular membrane, Biomembrane. B. The hist
3、ory of study Overton(1890s): Lipid nature of PM;, J.D.Robertson(1959): The TEM showing:the trilaminar appearance of PM; Unit membrane model; S.J.Singer and G.Nicolson(1972): fluid-mosaic model; K.Simons et al(1997): lipid rafts model; Functional rafts in Cell membranes. Nature 387:569-572,2. Singer
4、and Nicolsons Model of membrane structure: The fluid-mosaic model is the “central dogma” of membrane biology.,The core lipid bilayer exists in a fluid state, capable of dynamic movement. Membrane proteins form a mosaic of particles penetrating the lipid to varying degrees.,The Fluid Mosaic Model, pr
5、oposed in 1972 by Singer and Nicolson, had two key features, both implied in its name.,3. The chemical composition of membranes,A. Membrane Lipids: The Fluid Part of the Model,Phospholipids: Phosphoglyceride and sphingolipids Glycolipids Sterols ( is only found in animals),Membrane lipids are amphip
6、athic. There are three major classes of lipids:,Figure 10-2. The parts of a phospholipid molecule. Phosphatidylcholine, represented schematically (A), in formula (B), as a space-filling model (C), and as a symbol (D). The kink due to the cis-double bond is exaggerated in these drawings for emphasis.
7、,Figure 10-3. A lipid micelle and a lipid bilayer seen in cross-section. Lipid molecules form such structures spontaneously in water. The shape of the lipid molecule determines which of these structures is formed. Wedge-shaped lipid molecules (above) form micelles, whereas cylinder-shaped phospholip
8、id molecules (below) form bilayers.,Figure 10-4. Liposomes. (A) An electron micrograph of unfixed, unstained phospholipid vesicles (liposomes) in water. The bilayer structure of the vesicles is readily apparent. (B) A drawing of a small spherical liposome seen in cross-section. Liposomes are commonl
9、y used as model membranes in experimental studies. (A, courtesy of Jean Lepault.),Figure 10-5. A cross-sectional view of a synthetic lipid bilayer, called a black membrane. This planar bilayer is formed across a small hole in a partition separating two aqueous compartments. Black membranes are used
10、to measure the permeability properties of synthetic membranes.,Figure 10-6. Phospholipid mobility. The types of movement possible for phospholipid molecules in a lipid bilayer.,Figure 10-7. Influence of cis-double bonds in hydrocarbon chains. The double bonds make it more difficult to pack the chain
11、s together and therefore make the lipid bilayer more difficult to freeze.,Figure 10-8. The structure of cholesterol. Cholesterol is represented by a formula in (A), by a schematic drawing in (B), and as a space-filling model in (C).,Figure 10-9. Cholesterol in a lipid bilayer. Schematic drawing of a
12、 cholesterol molecule interacting with two phospholipid molecules in one leaflet of a lipid bilayer.,Figure 10-10. Four major phospholipids in mammalian plasma membranes. Note that different head groups are represented by different symbols in this figure and the next. All of the lipid molecules show
13、n are derived from glycerol except for sphingomyelin, which is derived from serine.,Figure 10-11. The asymmetrical distribution of phospholipids and glycolipids in the lipid bilayer of human red blood cells. The symbols used for the phospholipids are those introduced in Figure 10-10. In addition, gl
14、ycolipids are drawn with hexagonal polar head groups (blue). Cholesterol (not shown) is thought to be distributed about equally in both monolayers.,Figure 10-12. Glycolipid molecules. Galactocerebroside (A) is called a neutral glycolipid because the sugar that forms its head group is uncharged. A ga
15、nglioside (B) always contains one or more negatively charged sialic acid residues (also called N-acetylneuraminic acid, or NANA), whose structure is shown in (C). Whereas in bacteria and plants almost all glycolipids are derived from glycerol, as are most phospholipids, in animal cells they are almo
16、st always produced from sphingosine, an amino alcohol derived from serine, as is the case for the phospholipid sphingomyelin. Gal = galactose; Glc = glucose, GalNAc = N-acetylgalactos-amine; these three sugars are uncharged.,Figure 10-13. Six ways in which membrane proteins associate with the lipid bilayer. Most trans-membrane proteins are thought to extend across the bilayer as a single a helix (1) or as multiple a helices (2); some of
