Lecture 2--membranes

Endo cytosis also going on also bringing in membrane

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Unformatted text preview: . also bringing in membrane. Intracellular Membranes • • • Membranes that form organelles have the same basic composition as the plasma membrane. bilayer, but can have different proteins within it However, the overall composition of lipids and proteins differs significantly. Plasma membrane composition differs from cell to cell Cell membranes contain many chemically distinct kinds of lipids with different properties phospholipids glycerl, phosphate group, and other group, and hydroophobi c tails (saturated or unsaturated) Different membranes in a cell contain different complements of lipids summary of how different organelles have different c omposition. van Meer G, Voelker DR, Feigenson GW (2008). Membrane lipids: where they are and how they behave. Nat Rev Mol Cell Biol. 9(2):112-24. How do different lipids end up in different membranes? ER Selective transport: Lipids made in the ER or incorporated from the outside are trafficked to different destinations in a cell. How do different lipids end up in different membranes? PI3kinase onc lipid put in membrane, chemical structure can be c hanged by enzyme. Lipids can be phosphorylated or dephosphorylated to endow their head groups with different chemical properties How do different lipids end up in different membranes? Lipids can be cleaved by lipases How do different lipids end up in different membranes? Flippases, floppases and scramblases are enzymes that use energy from ATP to exchange lipids from one leaflet to another Clark, MR (2011). Flippin' lipids. Nature Immunology 12: 373–375. How do different lipids end up in different intracellular membranes? • Newly formed lipids are transported to specific locations Lipids can be covalently modified; for example, they can be phosphorylated, dephosphorylated or cleaved • Lipids can be flipped from one leaflet to another • PI3kinas lipids and proteins in the membrane can diffuse laterally-- “fluid mosaic” Singer and Nicolson model Singer and Nicolson (1972) Science integral membrane proteins, directly inerted in membranes inside of membrane hydrophobic, this dictates how proteins will interacts with membrane (lipid portion interact with bilayer proteins that span the membrane, the amino acida that are in the membranes are hydrophobic themselves lowering temperature below 15 degrees slowed Singer andmNicolson thermally controlledScience (1972) ixing, why? fluidity is lipids can move laterally with respect to each other. process, if membrane less fluid, the proteins would move slower and take longer to intermix; temperature affect composition of bilayer indirect immuno fluorescence if you use more than one antoibody human cell: rabbit anti human, goat anti rabbit; mouse cell: mouse anti mouse; goat anti mouse; shortly after cell fusion; they were largly s egregated, about 40 minutes later, the c omponents were almost xompletely intermixed suugested that proteins mixing; why did they block protein synthesis? want to look at protein that w...
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