Membrane Transport

Membrane Transport - Membrane Transport Membrane Transport...

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Membrane Transport
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Membrane Transport
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Overview of Membranes Membranes are barriers; lipids block passage of most water-soluble molecules Transport and communication between cell and extracellular environment must occur across the plasma membrane; nutrients, gases, ions Plasma membrane then serves two functions: 1) retains cell contents so they do not leak out (sugars, amino acids, ions; 2) allows necessary exchange of material in and out of the cell (respiratory gases, hormones, waste products, etc. Transport of material and information is selective
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How Are Materials Transported Across the Plasma Membrane? In bulk form: examples by exocytosis of vesicles ( enzymes; mucus); endocytosis (yolk in egg cells; insulin receptors) As solutes dissolved in fluid: gases, ions and small organic molecules (amino acids, monosaccharides, nucleotides)
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Permeability of the Lipid Bilayer
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Mechanisms of Transporting Solutes Across Membranes Simple Unassisted Diffusion thru lipid bilayer Facilitated Diffusion – involves assistance from a transport protein – energy-independent - glucose uptake by RBCs; or channel protein: aqueous pore; Active Transport – energy- dependent with transporter proteins- uptake of glucose, lysine by small intestine
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Mechanisms of Movement Across Membranes
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Factors that Affect Crossing A Membrane Size – small/large; Polarity – polar/nonpolar Ion - charge/uncharged
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Simple Diffusion (Unassisted Net Movement of a Solute Down A Gradient) A spontaneous process that depends on the random thermal motion of molecules Solute moves from region of higher concentration to region of lower concentration; movement is always toward equilibrium (minimum free energy); can be bidirectional
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This note was uploaded on 11/09/2011 for the course CELL BIO & 270 taught by Professor Hart during the Fall '08 term at Rutgers.

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Membrane Transport - Membrane Transport Membrane Transport...

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