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LIPIDS Primarily C and H atoms (hydrophobic) Energy storage (~80% total), membranes, signaling molecules Four families: fats, phospholipids, steroids, and waxes 1. Fats Compact energy storage Thermal insulation for animals Cushions organs Triacylglycerols (triglycerides) Three fatty acids attached to a glycerol molecule (not a polymer) fatty acid fatty acid fatty acid Glycerol Triacylglycerol (TAG) Fatty acids are usually 16 or 18 carbon atoms long nonpolar → hydophobic Triacylglycerol Formation Condensation reaction between a hydroxyl group of glycerol and the carboxyl group of a fatty acids **Dehydration synthesis** o Forms an ester linkage (esterification) Ester linkage Saturated fats hydrocarbon chains saturated with H atoms (no double bonds) Straight chains fit closely together → London forces along their length → SOLIDS at room temperature Predominantly produced by animals Unsaturated fats 1+ carbon-carbon double bonds o Polyunsaturated fatty acids = many double bonds Double bond causes a bend in the fatty acid, reducing the strength of the London forces → LIQUIDS at room temperature (oils) Predominantly produced by plants (olive oil, canola oil, etc.) ****Hydrogenation Industrial process where H-atoms are added to double bonds in unsaturated fatty acids → semi-solids (margarine and shortening) Produces trans fats (almost all natural fat = cis fats) cis trans 2. Phospholipids Glycerol molecule attached to 2 fatty acid chains and a phosphate Amphipathic: Hydrophilic heads (phosphate group) and hydrophobic tails (fatty acids) When in water phospholipids form spheres called micelles or produce phospholipid bilayers ( liposomes) o Hydrophilic head faces the aqueous environment and the hydrophobic tails are tucked away from contact with water Polar molecules can not pass through the membrane because of the nonpolar centre Cell membranes contain proteins and hydrophilic pores that allow polar material to pass 3. Sterols: Steroids Compact hydrophobic molecules containing 4 fused hydrocarbon rings and several functional groups Different steroids have different functional groups attached Lacks a fatty acid component Cholesterol Precursor of all steroid hormones (e.g. sex hormones) and other compounds such as vitamin D and bile salts Also present in cell membranes, where it increases membrane rigidity Cholesterol Estrogen Testosterone 4. Waxes Long-chain fatty acids linked to alcohols or carbon rings Hydrophobic with firm, pliable consistency Used as waterproof coatings by plants (leaves, stems, etc.) and animals (bird feathers, beeswax, etc.) Omega fats Essential fatty acids that cannot be made by the body alpha-linolenic acid (ALA), an essential n−3 fatty acid eicosapentaenoic acid (EPA). Linoleic acid (LA) Lipoproteins Protein-lipid complexes that carries fat in the blood HDL - High Density Lipoprotein (good cholesterol) - High protein/fat ratio - scavengers – collect fat from body and return to liver LDL - Low Density Lipoprotein (bad cholesterol) - High fat/protein ratio - Transports fat from liver → body