L10. Biological membrane Terms: lipid bilayer saturated fatty acid ahelix phospholipid unsaturated fatty acid hydropathy analysis amphipathic cholesterol b-barrel hydrophilic head group integral membrane protein glycoprotein hydrophobic fatty acid tails peripheral membrane protein glycolipid hydrophobic effect micelle liposome transmembrane protein Topics: (1)Functions of biological membrane (2)Structure and properties of biological membrane (3)Membrane proteins Reading:Chapter 11, skipthe sections from pg. 366 last paragraph to pg. 368, and from pg. 373, second paragraph to pg. 377, first paragraph. Lecture Summary: 1.Functions of biological membranes •Boundary •Transport of proteins and lipids via membrane vesicles •Transport of ions and small molecules in and out of the cell and organelles via transport proteins spanning the membrane •Receiving and transferring information from environment and neighboring cells via proteins spanning the plasma membrane •Expansion of plasma membrane drives cell motility 2.Structure and properties of biological membranes •A biological membrane is a lipid bilayer. The backbone of a lipid bilayer is composed of phospholipids. -Phospholipids are amphipathic, with a hydrophilic (polar) head group and two hydrophobic (non-polar) tails. -Hydrophobic effect: aggregation of hydrophobic fatty acid tails is energetically favorable, promotes the assembly of a lipid bilayer -Hydrophilic head group allows the lipid bilayer to interact with its aqueous environment -Biological membrane spontaneously forms self-sealed, closed compartment in an aqueous environment. It is energetically unfavorable to expose free edges of a lipid bilayer. When free edges are created by rupturing the membrane, the membrane self-seals due to hydrophobic effect from the fatty acid tails of phospholipids. -Liposomes are double-layered closed vesicles that are formed when purified phospholipids are added to water.