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Topic Talks Unit 1: Cell & Transport, Cell Signalling

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PHGY 210
Allan R Baer

TopicTalksUnit1-CellsandTransport • Cell surface/membrane made of phospholipid bilayer = lipophilic • Diffusion: free to move across cell membrane (CM) • List of characteristics to increase diffusion rate: 1.Small: small enough to pass through cell membrane 2.Lipophilic: like dissolves like, lipophilic molecules are able to move freely across 3.Short diffusion distance: increases diffusion rate, smaller distance to cross 4.Increased permeability: allows for greater concentration to diffuse through 5.Increased SA 6.No charge 7.Moves down conc gradient • H2O freely permeable to most CM • • for ions/molecules that are bigger/lipophobic (water-soluble)/carry a charge and need to cross CM to enter cell, require membraneproteincarrier/transporter to move across lipid bilayer • Facilitatedtransport: protein channels/carriers that move molecules downconcgradient • conc of ion/molecule must be higher outside cell than inside, moves into cell through conc gradient • noenergyextra needed to this transport method • Ex:urea transporters, glucose, sugar transport • • Activetransport: movement of molecules againstconcgradient • needsenergy& transporter in order to move ion/molecule into cell • usuallyATPenergy used - ATPasepumps • Ex:Na+/K+ ATPase - pumps 3 Na+ out & 2 K+ in (against both their gradients) • • Secondaryactivetransport: use of energy/ATPase indirectly to move an ion/molecules across CM • often uses Na+concgradthru active transport, leads to lower Na+ conc inside cell • other transporters can make use of low Na+ by letting Na+ leakbackinside down its conc gradient (no energy used) • @ same time, can coupleNa+ movement with anothermoleculeeither inside/out a cell • Antiporter: moves in opposite dir ex: Na+/glucose co-transport (in kidneys) • Symporter: moves in same dir ex: Na+/Ca2+ exchange (in heart, Ca2+ out of cardiac muscle cells) • ATP isn't directly involved in the transport of that ion/molecule, but does depend on Na+ gradient crea
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