The Lipid Bilayer
- The lipid bilayer is the basic double-layer structure that gives the plasma membrane its barrier function.
- Lipid-soluble molecules dissolve well in lipids, so they can pass through the fatty interior of the membrane more easily than charged molecules can.
- Nonpolar molecules have no major separation of electrical charge, so they pass through the nonpolar membrane interior more easily than ions do.
- Small lipid-soluble, nonpolar molecules can cross the lipid bilayer because their chemical properties match the membrane interior.
- Ions are atoms or molecules with an electrical charge.
- Charged ions do not cross the lipid bilayer freely because the membrane interior repels charged particles.
- The lipid bilayer creates the need for channels, carriers, and pumps whenever a charged or strongly water-soluble substance must cross the membrane.
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