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LIPIDS AND MEMBRANES Fatty acids H H C C H H •Hydrocarbon chain (saturated or un-) •Carboxylic acid group Fatty acids Nomenclature: C1 (COOH), C2, C3, etc. αC = C2, ßC = C3, etc. 18 C’s with 2 double bonds: C18:2(Δ9,12) (“Δ9” means between C9 and C10) (double bonds are normally at 9, 12, 15 and are cis) • • • • Palmitic acid—C16:0 Stearic acid—C18:0 Oleic acid—C18:1 (Δ9) Linoleic acid—C18:2 (Δ9,12) Fatty acids • • • • Palmitic acid—16:0 Stearic acid—18:0 Oleic acid—18:1 (Δ9) Linoleic acid—18:2 (Δ9,12) Long, straight chains are less soluble (in aqueous medium) Short chains, and double bonds reduce melting temperature and increase solubility Long chain n-3 polyunsaturated fatty acids (PUFA), found in fish oil but probably synthesized by algae in fish diets, have important effects on human health. http://www.uptodate.com/contents/fish-oil-and-marine-omega-3-fatty-acids Long chain saturated fatty acids are pheromones for many insects, advertising fecundity in queens and/or suppressing reproduction in workers. Van oystaeyen et al., Science 343, 287 (17 Jan 2014) Triacyl glycerol: energy storage (fats and oils): 38 kJ/mol (vs protein 17 kJ/mol) Fats and oils --storage forms of C and energy-- accumulate in lipid bodies An adipocyte Membrane lipids (phospholipids) glycerol C1-attached fatty acid normally saturated glycerol C2-attached fatty acid normally unsaturated glycerol C3: phosphate plus hydrophilic group... Membrane lipids (phospholipids): note the different head groups Other lipids: e.g. sphingolipids on a sphingosine base See below: sphingosine is outlined Membranes Lipid bilayer: heads in contact with aqueous solution; tails isolated from it. Note the different lipids in membranes: inner and outer leaflets are distinct. erythrocyte: • inner: phosphatidylethanolamine, phosphatidylserine predominate • outer: phosphatidyl choline, sphingomyelin predominate P-lipid breakdown by hydrolysis: catalyzed by phospholipases e.g.: snake venom P-lipase (PLA2) hydrolyzes C2 fatty acid, which bursts erythrocytes Sterols: note tetra-ring base, hydrophobic addition, hydrophillic -OH Archeal membrane lipids have structures analogous to phospholipids Lipid solubility ! on water surface: heads in water, tails in air ! submerged single tail lipids (e.g., sodium laurylsulfate) at “critical micelle concentration”: spontaneous formation of micelles ! submerged phospholipids form liposomes, bilayer leaflets Phase transitions • longer chains raise the transition temperature, decrease fluidity • double bonds lower the transition temperature, increase fluidity • membranes leak during the transition • cholesterol (et al.) makes the gel more fluid and the liquid crystal less fluid (also Ca2+) • enzymes in membranes generally work better in liquid crystal phase, but complexes may stay together better in a gel Resistance to cold is associated with higher concentrations of linolenic acid. Olive oil “Tests indicate that imported “extra virgin”olive oil often fails international and USDA standards - UC Davis Olive Center, July 2010” Lipid composition Unsaturated Palmitic acid: 7.5–20.0% Stearic acid: 0.5–5.0% Mono-unsaturated Oleic acid: 55.0–83.0% Palmitoleic acid: 0.3–3.5% Polyunsaturated Linoleic acid: 3.5–21.0 % α-Linolenic acid: <1.5% Problems Free fatty acids Peroxides UV absorption (conjugated double bonds) 1,2 and 1,3 diacylglycerols Summary Fatty acids are distinguished by length and presence of double bonds: palmitic, steric, oleic, and linoleic acids are common. Storage lipids are generally triglycerides Membrane lipids include phospholipids, sphingolipids, and sterols Temperature-induced phase transitions represent a change from close-packed to more open conformations