BCHE 395-16 2014 Membranes and Transport I

Solute concentra8on andor electrochemical gradients

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Unformatted text preview: d amino acids are only found in aqueous domains β- barrels in Membrane Proteins Examples are all E. coli proteins IRON UPTAKE MALTOSE TRANSPORTER PHOSPHOLIPASE Lipid Anchors •  Some membrane proteins are lipoproteins •  They contain a covalently linked lipid molecule –  Long- chain fa\y acids –  Isoprenoids –  Sterols –  Glycosylated phosphaFdylinositol (PGI) •  The lipid part can become part of the membrane •  The protein is now anchored to the membrane –  reversible process –  allows targeFng of proteins –  Some, such as GPI anchors are found only on the outer face of plasma membrane Lipoproteins Examples Myristoyl groups (carboxyl- terminal Cys) Prenyl groups (amino- terminal Gly) Palmitoyl groups (Cys of Ser) Membrane ComposiFon •  So how do fish and mammals live in the ArFc/AntarcFc oceans? Why don’t their cell membranes solidify? •  Turns out cells can regulate their lipid composiFon to achieve constant membrane fluidity Study of Membrane Dynamics •  Rates of lipid lateral diffusion are high (up to 1 µm/sec): –  a lipid can circumnavigate E.coli cell in one second •  (1) Fluorescence Recovery AUer Photobleaching (FRAP): technique that monitors lateral lipid diffusion by monitoring the rate of fluorescence return –  A\ach fluorescent tags to lipids all over the cell, bleach and monitor Fme it takes to populate bleached area with fluorescently tagged lipids •  (2) Hop Diffusion: monitoring the path of a single lipid in Fme –  A\ach a fluorescent tag to a single lipid and record by fluorescence microscopy over Fme FRAP: Lipid Step 1: Label Outside of Cell Step 2: Photobleaching Step 3: Measure Recovery Hop Diffusion: Lipid Movement of a Single Lipid in 56 ms Regulates cellular traffic Membrane Transport •  Membrane transport: specific and dependent on solute concentra8on and/or electrochemical gradients •  Nutrient uptake (glucose, amino acids, etc.) •  Ionic homeostasis (Na+, K+, Ca2+, etc.) •  Inter- compartment traffic (ATP in mitos) •  IntesFnal absorpFon of nutrients •  Renal excreFon/retenFon •  Fast signaling (nerve, muscle, etc.) •  Even water is transported (aquaporins) Diffusion of Molecules Membranes are flexibl...
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