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Transcript
Harvey Lodish • Arnold Berk • Paul Matsudaira • Chris A. Kaiser • Monty Krieger • Matthew P. Scott • Lawrence Zipursky • James Darnell Molecular Cell Biology Fifth Edition Chapter 5: Biomembranes and Cell Architecture Copyright © 2004 by W. H. Freeman & Company Plasma membrane 1. Affect shape and function 2. Anchor protein to the membrane 3. Modify membrane protein activities 4. Transducing signals to the cytoplasm Lipid Bilayer 1. Impermeable barrier prevent diffusion of water soluble solute 2. Membrane protein mediate transport of specific molecule 3. Maintained by hydrophobic interaction Van der waal interaction between membranes RBC Smooth and flexible Long , slender extension Multiple layers of modified plasma membrane: formed by adjacent glial cells The faces of cellular membrane 1. Internal faces surface orient toward the interior of the compartment 2. External faces the surface presented to the environment Chloroplast in plants 磷酸甘油酯 i.e.plasminogen Acyl group: c16 or c18, 0, 1 or 2 double bond choline head膽鹼 鞘酯 sphingomyelin glucosylcerobroside Hydrocarbon chain Four ring hydrocarbon amphipathic FRAP: Fluorescent Recovery After Photobleaching Most lipids and proteins are laterally mobile in biomembrane Lipid composition influence physical properties of membrane: 1. Different composition of organs 2. Specialized membrane function i.e. apical surface if intestinal lumen sphingolipids: phosphoglycerides: cholesterol basolateral apical 0.5 1 1 1 1 1 3. Affects membrane fluity a. short C-H chain are more fluid b. kinks in C-H: less stable Long saturated fatty acyl chain heat Decreased thickness 4. Influence thickness of membrane 5. Local curvature Larger head Smaller head bilayer enriched with PC in the exoplasmic leaflet and with PE in the cytoplasmic face would cause the natural curvature Membrane asymmetry Affects: 1. Enzyme cleavage phospholipase cleaves phospholipids at exoplasmic sides cytosolic sides are resist to phospholipase cleavage Cleave phospholipid at cytosolic side 2. Membrane based functions i.e. signal transduction pathway of phosphotidyl inositol Cleavage by phospholipase C PI + Diacylglycerol( DAG) Activation of signal transduction pathway i.e. phosphotidyl serine stimulation of platelate by serum translocate to exoplasmic face activate enzyme for blood clotting Lipid Raft micro domain of cholesterol, sphingolipids and certain membrane protein GM1: glycosphingolipids PLAP: placental alkaline phosphatase TfR: transferrin receptor Three categories of membrane protein 1. Integral membrane protein( transmembrane protein) a. exoplasmic domain cytosolic domain hydrophilic b. Membrane spanning domain: hydrophobic c. glycosylated 2. Lipid anchored membrane protein covalently bound to lipid 3. Peripheral membrane protein bound to membrane by interaction with integral membrane protein Glycophorin A: a typical single pass transmembrane protein -helices Binding of Arg or Lys to negatively charged head of phospholipid -helices: 20-25 hydrophobic amino acids Interact with fattyacyl of lipid by van- der-waals G protein: 7-multipass bacteriorhodopsin retinal Porin Trimric tramsmembrane protein Barrel shape subunit with ßsheet wall and hydrophilic center aliphatic and aromatic side chain position the protein on the membrane Anchoring of plasma membrane proteins to the bilayer by covalently linked hydrocarbon group 1. anchor by fatty acyl group 2. Anchor by unsaturated fatty acid to cyctein at or near C terminal 3. GPI anchoring lipid anchor on membrane is glycosyl phosphotidyl inositol( GPI) sugar Gly C14 or C16 Glycosylphosphosphatidylinositol Cys C15 or C20 All transmembrane proteins and glycolipids are asymetrically oriented in the bilayer Motility of membrane protein 1. Float freely 2. Immobile 3. Anchored by cytoskeletal protein PH ( pleckstrin homology domain) Interfacial binding surface and mechanism of action of phospholipase A2 Effects of external ion concentration on water flowacross the plasma membrane of an animal cells