细胞膜的结构及探索历程课件.ppt
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- 细胞膜 结构 探索 历程 课件
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1、细胞质膜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;Singer and Nicolsons Model of membrane structure:The fluid-mosaic model is the“centr
2、al dogma”of membrane biology.The Fluid Mosaic Model,proposed in 1972 by Singer and Nicolson,had two key features,both implied in its name.Figure.The parts of a phospholipid molecule.Phosphatidylcholine(PC,磷脂酰胆碱),represented schematically(A),in formula(B),as a space-filling model(C),and as a symbol(D
3、).The kink due to the cis-double bond(顺双键)is exaggerated in these drawings for emphasis.Figure.A lipid micelle(微囊)(微囊)and a lipid bilayer seen in cross-section(横断面)(横断面).Lipid molecules form such structures spontaneously in water.The shape of the lipid molecule determines which of these structures i
4、s formed.Wedge-shaped lipid molecules(above)form micelles,whereas cylinder-shaped phospholipid molecules(below)form bilayers.Figure.Liposomes(脂质体)(脂质体)(A)An electron micrograph of unfixed,unstained phospholipid vesicles(liposomes)in water.The bilayer structure of the vesicles is readily apparent.(B)
5、A drawing of a small spherical liposome seen in cross-section.Liposomes are commonly used as model membranes in experimental studies.Figure.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
6、)or as multiple a helices(2);some of these“single-pass”and“multipass”proteins have a covalently attached fatty acid chain inserted in the cytoplasmic monolayer(1).Other membrane proteins are attached to the bilayer solely by a covalently attached lipid-either a fatty acid chain or prenyl group-in th
7、e cytoplasmic monolayer(3)or,less often,via an oligosaccharide,to a minor phospholipid,phosphatidylinositol(磷脂酰肌醇),in the noncytoplasmic monolayer(4).Finally,many proteins are attached to the membrane only by noncovalent interactions with other membrane proteins(5)and(6).Membrane proteinsFigure.A ty
8、pical single-pass transmembrane protein.Note that the polypeptide chain traverses the lipid bilayer as a right-handed a helix and that the oligosaccharide chains and disulfide bonds are all on the noncytosolic surface of the membrane.Disulfide bonds do not form between the sulfhydryl groups in the c
9、ytoplasmic domain of the protein because the reducing environment in the cytosol maintains these groups in their reduced(-SH)form.(3)Figure.The covalent attachment of either of two types of lipid groups can help localize a water-soluble protein to a membrane after its synthesis in the cytosol.(A)A f
10、atty acid chain(either myristic or palmitic acid)is attached via an amide linkage to an amino-terminal glycine.(B)A prenyl group(either farnesyl or a longer geranylgeranyl group-both related to cholesterol)is attached via a thioether linkage to a cysteine residue that is four residues from the carbo
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