CAS NE 102 Lecture 10: Ch. 12 membrane transport

• School: Boston University
• Department: Neuroscience
• Course: CAS NE 102
• Professor: Lucia Pastorino

Document Summary

Pic: cell membranes contain specialized membrane transport proteins that facilitate the passage of selected small water-soluble molecules. A) liposome with no membrane proteins impermeable to most water-soluble molecules. B) cell membranes contain transport proteins that each transfer a particular type of molecule. Selective transport includes active pumping of specific molecules out or into cell. Pic: lipid bilayers are impermeable to most ions and uncharged polar molecules. Rate of diffusion across protein-free lipid bilayer depends on molecule"s size and solubility. Smaller molecule and the fewer its favorable interactions with water (less polar), the more rapidly the molecule diffuses across the bilayer. Most of the organic molecules a cell uses as nutrients (red) are too large and polar to pass through bilayer that does not contain membrane-transport proteins. Small nonpolar molecules: (oxygen, carbon dioxide) dissolve readily in lipid bilayers and rapidly diffuse across them. Cells depend on permeability to gases for respiration processes.