L3940_memtrans_462A_2013sm

Ac4ve transport primary secondary nonpolar polar polar

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Unformatted text preview: also be described by the number of substrates and the direcGons in which they are transported •  Note: EnergeGcs is not considered in this categorizaGon single substrate two substrates move in the same direcGon move in the opposite direcGon Movement Transporters classificaGon Diffusion Type Passive Polarity of molecule Energe4cs Facilitated Ac4ve Transport Primary Secondary Nonpolar Polar Polar Polar Favorable Favorable Unfavorable Unfavorable Made N/A favorable by coupling to: N/A Hydrolysis of ATP Transport of a different ion or molecule down its electrochemical gradient Example GLUT1 Ion channels Porins P Type ATPase Lactose permease ABC transporters F ATPase •  Facilitated diffusion / Passive transport –  –  –  –  GLUT1 Chloride ­bicarbonate exchanger Aquaporins Ion Channels •  K+ channel •  voltage gated K+ channel •  ligand gated – acetylcholine receptor •  Primary AcGve Transport –  –  –  –  SR Ca2+ ATPase Na+  ­ K+ ATPase FoF1 ATPase/ATP synthase ABC transporters •  Secondary AcGve Transport (co ­transport) –  Lactose permease Channels facilitate the rapid movement of ions across membranes Ion Channels Facilitated diffusion •  Three types: –  regulated or “gated” by ligands –  regulated or “gated” by voltage changes –  resGng channels that are unregulated •  Movement of ions across cell membranes is criGcal for establishing resGng membrane potenGal and an acGon potenGal Potassium Channel •  Tetrameric struture •  Transports K+ ions down their concentraGon gradient •  Rates of transport: ~ 108 ions/s •  100  ­ fold more permeable to K+ than Na+ ions ! Aquaporin – Water Channel Allows passage of water molecules, while prevenGng ions and other solutes, even H+ Prevent “proton hopping” Jensen, Tajkhorshiand Schulten Structure, 2001 Signaling in the nervous system •  Electrical signal produced by the flow of ions across the membrane •  Change in membrane voltage triggers channel gate ­opening and ions movement AcGon PotenGal (Nerve Impulse) Electrical signal produced by the flow of ions across the membrane Res4ng High Na+ Low K+ Firing (channels) Na+ Recovering (Na/K pump) K+ Low Na+ High K+  ­60 mV Neuron K+ up to 30 mV (propagates) Na+ back to  ­60 mV Voltage ­gated channels Regulated by change in membrane potenGal S4: 5 posiGvely charged side chains spaced about every 3 residues Membrane potenGal increases (inside less negaGve): S4 is pulled toward the extracellular side of the membrane Voltage changes induce conformaGonal changes that open...
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This test prep was uploaded on 02/25/2014 for the course BIOC 462A taught by Professor Ziegler,baldwin during the Spring '08 term at University of Arizona- Tucson.

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