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SL+D103+lecture+4 - D103: Cell Biology Dr. Shin Lin Lecture...

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D103: Cell Biology Dr. Shin Lin
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Lecture 4 Biological Membranes III: Transport Functions (Channels) Recommended Reading : MBOC (5th edition) 667-694
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D103 Fall 2011 Lecture 4 © Lin All rights reserved Review of Membrane Transport Proteins Transporters • Uniporter: facilitates diffusion of solute down its gradient • Symporter and Antiporter: move solutes up their gradients, driven by cotransported ions down their gradients • Pumps: use ATP to move solutes against their gradients Channels • transport solutes down their gradients through channels 3
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D103 Fall 2011 Lecture 4 © Lin All rights reserved Channels I. What can channels do for the cell? II. Properties of ion channels III. Membrane potentials IV. Action potentials 4
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D103 Fall 2011 Lecture 4 © Lin All rights reserved What can channels do for the cell? In the cell, both ion channels and ion pumps contribute to the formation of the membrane potential – Difference in voltage (electric potential, separation of charge) across the membrane The ionic gradients and electric potential across the membrane play important roles in biological processes : 1. Signaling Movement of Ca ++ into certain cells initiates processes such as muscle contraction or secretion 2. Transport Movement of Na + into cells drives uptake of glucose and other molecules up their gradients into the cell 3. Nerve cell signal Opening and closing of ion channels in response to changes in membrane potential create action potentials 5
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D103 Fall 2011 Lecture 4 © Lin All rights reserved I. What can channels do for the cell? II. Properties of ion channels 1. Ion channels are selective 2. Ion channels are gated 3. Ion channels have a high transport rate 4. Channel-mediated transport is saturable III. Membrane potentials IV. Action potentials 6
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D103 Fall 2011 Lecture 4 © Lin All rights reserved 7 General Characteristics of Channels Channels form hydrophilic passageways across membrane to transport ions, water, small molecules Transport through channels occurs
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SL+D103+lecture+4 - D103: Cell Biology Dr. Shin Lin Lecture...

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