BLG 311 Lecture Notes - Lecture 4: Voltage-Gated Potassium Channel, Membrane Transport Protein, Electrochemical Gradient
25 Nov 2016
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Section 4 membrane transport of small molecules and the electrical properties of. Membrane permeability is inversely proportional to size, polarity and charge. Ex: water permeates that membrane 10^9 times faster than small ions. Small nonpolar molecules can cross very well. Large and polar molecules are very difficult to cross. The more charged and the larger the molecule, the slower the diffusion across the membrane. Ion concentrations inside and outside a typical mammalian cell. Besides cl- there are many other negative charges: hco3-, Shown are concentrations of free cytosolic ions (not bound to other molecules and not inside organelles) Na+ and ca2+ are more abundant outside of the cell, less concentrated in the cell. Therefore, the cell needs mechanisms to allow specific molecules to cross the membrane barrier: Membrane transport proteins are specific for one or few types of molecules. All membrane transport proteins are multi-pass integral membrane proteins. There are two types: (the difference is how they operate: channels, carriers/permeases.
