I. Membranes<\/p>\n
Definition –Protective and selective barrier<\/em><\/p>\n II. Plasma membranes<\/p>\n A. Functions<\/p>\n 1. Separates the intracellular and extracellular compartments.<\/p>\n 2. Extraordinarily thin: 4-20 nm.<\/p>\n 3. Selective barrier.<\/p>\n 4. Detects chemical signals.<\/p>\n 5. Attachment site of filaments (e.g. cytoskeleton filaments).<\/p>\n B. Membrane Structure<\/p>\n 1. Double layer of lipids molecules in which proteins are embedded;Phospholipid bilayer.<\/strong><\/p>\n Fatty acid “tails” are\u00a0hydrophobic<\/strong>\u00a0but the phospholipid (has phosphate group) “head” is\u00a0hydrophilic<\/strong>.<\/em><\/p>\n 2. Lipids –Include Phosphoglycerides (glycerol based – a 3 carbon alcohol), Sphingolipids ( sphingosine based) and Cholesterol.<\/em><\/p>\n a. Phosphoglycerides and sphingolipids are\u00a0<\/em>amphipathic\u00a0<\/strong>molecules. One end is polar (water soluble). The other is nonpolar (lipid soluble).<\/em><\/p>\n b. Cholesterol– a steroid ring-shaped with C=C bond within the ring; by interacting with phospholipids, cholesterol can reduce permeability by filling gaps between phospholipids; cholesterol can increase membrane fluidity if there is enough cholesterol to block phospholipids from packing closely.<\/em><\/p>\n 3. Fluidity of the plasma membrane – Fluid Mosaic Model<\/p>\n a. Membrane fluidity depends on properties of membrane lipids which are influenced by the physical environment<\/p>\n b. Longer length of fatty acid chains and saturated chains lead to less fluid membranes & then proteins cannot move<\/p>\n c. Shorter length fatty acid chains and unsaturated chains lead to higher fluidity but cannot be to the point that the membrane liquefies completely and loses its integrity.<\/p>\n d. Note how animals at cold temperatures have more unsaturated tails to keep their membranes fluid at colder temps.<\/p>\n 4. Proteins are fewer in number than lipids but larger in size, so can make up to 50% of membrane<\/p>\n a. Integral proteins<\/strong>–\u00a0embedded in bilayer or spanning across entire membrane. Cannot be extracted without disrupting bilayer<\/em><\/p>\n b. Peripheral proteins<\/strong>–\u00a0located at the surface, usually attached to integral protein<\/em><\/p>\n c. Membrane protein functions<\/p>\n -Receptors<\/p>\n -Second messenger systems<\/p>\n -Ion channels<\/p>\n -Enzymes<\/p>\n -Carriers<\/p>\n <\/p>\n <\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" I. Membranes Definition –Protective and selective barrier II. Plasma membranes A. Functions 1. Separates the intracellular and extracellular compartments. 2. Extraordinarily thin: 4-20 nm. 3. Selective barrier. 4. Detects chemical signals. 5. Attachment site of filaments (e.g. cytoskeleton filaments). B. … Continue reading