Lecture 17 Pumps, Channels, and Membrane Potential

Lecture 17 Pumps, Channels, and Membrane Potential - IPHY...

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Unformatted text preview: IPHY 3060 Lecture 18: Pumps, Channels and Membrane Potential The plasma membrane is impermeable to charged ions How do we get ions across the plasma membrane? How do we get ions across the plasma membrane? With protein pumps and channels Membrane Pumps Move ions or other molecules across membranes against their concentration gradient primary active transport Energy for this is provided by ATP hydrolysis Functions of Membrane Pumps Establish electrochemical gradients by pumping ions in and out of cells Change pH by pumping H+ ions in and out of cells and organelles Pump drugs and toxins out of cells Synthesize ATP Example of a membrane pump: The Na+/K+ ATPase pump The Na+/K+ pump Found in the plasma membrane surrounding the cell Moves 3 Na+ out of cell and 2 K+ into cell, all against their concentration gradient Ion Channels Ion Channels Allow the movement of ions down their concentration gradientfacilitated diffusion Consist of 4 subunits arranged around a central pore Are specific for specific ionsP segment 3 Main Types of Ion Channels Nongated Ion Channels Voltage Gated Ion Channels Ligand Gated Ion Channels Nongated Ion Channel Example: The Resting K+ channel The Resting K+ Channel Allows K+ to move out of cell Even though it is not gated it can be either open or closed; opening and closing is independent of voltage or ligand binding Voltage Gated Ion Channels Structure of Voltage Gated Ion Channels P segment just like nongated channel, determines ion specificity Voltage-sensing alpha helix senses changes in voltage and undergoes conformational change, opening gated pore. Channel-inactivating segment swings into gate pore and blocks it, inactivating channel States of a Voltage-Gated Ion Channel Closed pore shut by voltage sensing alpha helices but not inactivated by inactivating segment Open pore open in response to movement of voltage sensing helices Inactivated pore closed and covered by inactivating segment Channelopathies Caused by mutations affecting the ion specificity, voltage sensitivity, opening, closing, or inactivation of ion channels Primarily affect excitable tissues such as brain & nervous system, heart, skeletal muscle Example: epilepsy & hyperactive voltage gated sodium channel Ligand-Gated Ion Channels: Ion channels that are opened by the binding of a specific substance Ligand-Gated Ion Channels Bind to various substances--- neurotransmitters, intracellular metabolites, etc Ligand binding changes opening and closing of ion channel The Electrochemical Gradient: The Electrochemical Gradient: The ionic composition of the cytoplasm differs from that of the fluid surrounding the cell at rest The ionic composition of the cytoplasm differs from that of the fluid surrounding the cell at rest...
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This note was uploaded on 08/11/2010 for the course IPHY 3060 taught by Professor Allen,davi during the Fall '09 term at Colorado.

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Lecture 17 Pumps, Channels, and Membrane Potential - IPHY...

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