Biochemistry 5: Lipid Structure and Functio Structural Lipids Signaling Lipids Characteristics: Lipids are insoluble in water and soluble in nonpolar organic solvents. Phospholipids: Amphipathic and form the bilayer of membranes. Contain a hydrophilic (polar) head and hydrophobic (nonpolar) tails. The head is attached by a phosphodiester linkage, and determines the function of the phospholipid. Saturation: Saturation of the fatty acid tails determines the fluidity of the membrane. Saturated fatty acid = less fluid. Glycerophospholipids: Phospholipids that contain a glycerol backbone. Sphingolopids: Contain a sphingosine backbone. Many (but not all) sphingolipid are also phospholipids with a phosphodiester bond. These are sphingophospholipids. Sphingomyelins: The major class of sphingophospholipids and contain a phosphatidylcholine or phohsphatidylethanolamine head group. Part of the myelin sheath. Terpenes: Odiferous steroid precursors made from isoprene. One terpene unit (monoterpene) contains 2 isoprene units. Terpenoids: Derived from terpenes via oxygenation or backbone rearrangement. Odorous characteristics. Steroids: Contain 3 cyclohexane rings and 1 cyclopentane. Steroid Hormones: Have high-affinity receptors, work at low concentrations, and affect gene expression and metabolism. Cholesterol: A steroid important to membrane fluidity and stability; and serves as a precursor to many other molecules. Prostaglandins: Are autocrine and paracrine signaling molecules that regulate cAMP levels. Affect smooth muscle contraction, body temp, sleep-wake cycle, fever, pain. Vitamins A, D, E, & K Fat soluble vitamins Vitamin A: Carotene, vision. Vitamin D: Cholecalciferol, bone formation. Vitamin E: Tocopherols, antioxidants. Vitamin K: Phylloquinone & menaquinones. Forms prothrombin, a clotting factor. Glycosphingolipids: Attached to sugar moieties instead of a phosphate group. Cerebrosides have 1 sugar connected to sphingosine. Globosides have 2 or more. Gangliosides: Contain oligosaccharides with at least 1 terminal Nacetylneuraminic acid (NANA). Waxes: Contain long-chain fatty acids esterified to longchain alcohols. Used as protection against evaporation and parasites in plants and animals. Steroid Energy Storage Phospholipid Polar head, nonpolar tails Triacylglycerols: Storage form of fatty acids. Contain 1 glycerol attached to 3 fatty acids by ester bonds. Very hydrophobic so do not carry additional water weight. Adipocytes: Animal cells used specifically for storage of large triacylglycerol deposits. Schematic of a phospholipid. May use glycerol or sphingosine for the backbone Free Fatty Acids: Unesterified fatty acids that travel in the bloodstream. Salts of free fatty acids are soaps. Saponification: The ester hydrolysis of triacylglycerols using a strong base like sodium or KOH. Micelle: Can dissolve a lipid-soluble molecule in its fatty acid core, and washes away with water because of its shell of carboxylate head groups. Cerebroside: A type of glycolipid. Any lipid linked to a sugar is a glycolipid Triacylglycerol