BIOS 20175 Lecture Notes - Lecture 16: Sodium Dodecyl Sulfate, Active Transport, Amphiphile
25 Jul 2020
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Document Summary
General strategies cells use to work within the rules of chemistry: enzyme catalysis, coupled reactions, compartmentation. Properties of biological membranes: impermeant to ions and other polar molecules, including protons, composed of phospholipids. Phospholipids are amphiphilic, with a polar head group and hydrophobic hydrocarbon tails. Phospholipids pack to form bilayers consisting of two leaflets. The most stable configuration of a phospholipid bilayer is a closed spherical shell: membranes are fluid: phospholipids can diffuse freely within a leaflet (but not between leaflets). So will detergents such as sodium dodecyl sulfate (sds). Whereas a phospholipid molecule is cylindrical, an sds molecule is conical. Hence, sds forms small globular micelles rather than flat bilayers. Hydrophobic compounds will partition into the hydrocarbon interior of a micelle. Phospholipids will also partition into a micelle => detergents solubilize membranes. Various transmembrane proteins have from one to 12 or more membrane-spanning domains: transmembrane proteins diffuse in a "sea of lipids" (the fluid mosaic model).
