Organization of the Cell

Membrane permeability gases and small uncharged

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Membrane Permeability Gases and small uncharged molecules will diffuse across the bilayer unassisted Passive Diffusion - Follows concentration gradient - No energy input - No transport proteins -Depends on relative hydrophobicity A measure of hydrophobicity: Partition coefficient (K) K = Cm / Caq eg. Urea, K = 0.0002 Diethylurea, K = 0.01 Passive Diffusion 15
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Membrane Transport ATP-powered pump - couples ATP hydrolysis with the movement of ions or molecules against gradient A c t i v e P a s s i v e Channel - allows ions or H2O molecules to cross membrane down gradient Transporter - binds ions or molecules, changes shape, transfers across membrane 16
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Passive Transporters Uniporter- move a single molecule down its concentration gradient Coupled Transport Moves a molecule against its gradient by using the force generated by the movement of another molecule down its concentration gradient Symporter- both molecules move in the same direction Antiporter- molecules move in the opposite direction 17
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http://www.youtube.com/watch v=LQD65eMHHvI Conformational Change Proteins are dynamic Alter shape in response environment -pH -binding 18
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[Glucose] high inside cell [Na+] high outside cell Glucose/Na+ Symporter Energy derived from movement of Na+ down its gradient used to move glucose 19
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Na+/K+ ATPase Essential to all life - Establishes gradients essential for several other transport processes Pumps 3 mlcs of Na+ out of cell and 2 mlcs of K+ into the cell BOTH ARE MOVING AGAINST THEIR CONCENTRATION GRADIENT 20
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Na+/K+ ATPase 21
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ABC Transporters ATP-powered pump ABC = ATP binding cassette Over 100 members Transport ions and various molecules 2 transmembrane and 2 ABC domains Medically relevant -MDR (cancer) -CFTR (cystic fibrosis) 22
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Substrate diffuses into the membrane Lateral association with MDR1 Promotes flipping across leaflet Substrate associates with intracellular domain of MDR1 MDR pumps substrate out through a pore MDR1 mechanism of action 23
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