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Lipids 1. Storage Lipids 2. Structural Lipids in Membranes 3. Working with Lipids
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Storage Lipids Fatty Acids - Structure Fatty Acids - Physical Properties Triacylglycerols - the simplest Lipids Triacylglycerols in Energy Storage Thermal insulation Triacylglycerols in food Waxes
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Fatty Acid Structure Carboxylic Acids (COOH is C1) hydrocarbon tails (C4 - C36) Saturated fatty acids N:0 Unsaturated Fatty acids Double bonds specified by (Δ n ) Branched or unbranced
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Fatty Acid Structure Carboxyl group (COOH) forms the acid. “R” group is a hydrocarbon chain.
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A Representative Fatty Acid
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Saturated Fatty Acid Unsaturated Fatty Acid
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Fatty Acids - Physical Properties Solubility Longer chains more hydrophobic, less soluble Double bonds increase solubility Melting points Depend on chain length and degree of unsaturation Double bonds- low melting temp Ex: At room temperature (25 C), the saturated fatty acids from 12:0 to 24:0 have a waxy consistency, Whereas, unsaturated fatty acids of these lengths are oily liquids.
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Triacylglycerols Glycerol head group HO-CH 2 -CH(OH)-CH 2 - OH Ester linkage from each hydroxyl to Fatty acid Carboxylate charge is lost TAGs more hydrophobic than FAs
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Synthesis of a Fat
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Triacylglycerols in Energy Storage & Thermal insulation In eukaryotic cell: TG as oily droplet in cytosol-metabolic fuel. Vertebrates: adipocyte cell (fat cell) store large amount of TG Oil in seeds, plants: providing energy and biosynthetic precursors for seed germination. Adipocyte cell and germinating seed containing Lipases that hydrolyze the ester linkages to release Fatty Acids
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Triacylglycerols in Energy Storage & Thermal insulation Advantages using TG as stored fuels over carbohydrates: Concentrated source of energy –Energy derived from oxidation reactions –More completely reduced state yields 2x the energy/g as Carbohydrates
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Triacylglycerols in Energy Storage & Thermal insulation TG as insulator: In some animals, triacylglycerols stored under the skin serve not only as energy stores but as insulation against low temperatures. Ex: Seals, penguins, other warm-blooded polar animals, hybernating animals (bears) etc.
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All C bonded to H No C=C double bonds long, straight chain most animal fats solid at room temp. contributes to cardiovascular disease (atherosclerosis) = plaque deposits Saturated fats Triacylglycerols in food
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Unsaturated fats C=C double bonds in the fatty acids plant & fish fats vegetable oils liquid at room temperature the kinks made by double bonded C prevent the molecules from packing tightly together Triacylglycerols in food
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Saturated vs. unsaturated saturated unsaturated
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Triacylglycerols in food Vegetable Oils (ex. Olive oil) : unsaturated, liquids at room temperature. converted industrially into solid fats by catalytic hydrogenation, which reduces some of their double bonds to single bonds.
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Waxes Esters of long chain fatty Acids with long chain alcohols Higher melting points Hydrophobic
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Summary Lipids are water insoluble Common Fatty Acids have 12-24 carbon atoms (an even number) Triacyl glycerols primary storage fats in food.
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Structural Lipids in Membranes Glycerophospholipids Ether Lipids Galactolipids and Sulfolipids in Chloroplasts Archael "Extremophile" Lipids Sphingolipids Lipid Degradation in Lysosomes Sterols Summary Some common types of storage and membrane lipids.
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Summary Polar Lipids major constituent of membranes Glycerophospholipids are charged depending on constituents Galactolipids are abundant in chloroplasts Archaebacteria have extreme lipids Sphingolipids are built on a sphingosine framework Sterols have a polycyclic aromatic ring structure
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Phospholipids Structure: – glycerol + 2 fatty acids + PO 4 PO 4 negatively charged It’s just like a penguin… A head at one end & a tail at the other!
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Phospholipids Hydrophobic or hydrophilic? – fatty acid tails = hydrophobic – PO 4 = hydrophilic head – dual “personality”
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Phospholipids in water Hydrophilic heads attracted to H 2 O Hydrophobic tails “hide” from H 2 O – can self-assemble into “bubbles” bubble = “micelle” can also form bilayer early evolutionary stage of cell? bilayer
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Why is this important? Phospholipids create a barrier in water – define outside vs. inside – cell membranes
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Phospholipids & cells Phospholipids of cell membrane – double layer = bilayer – hydrophilic heads on outside in contact with aqueous solution outside of cell and inside of cell – hydrophobic tails on inside form core – forms barrier between cell & external environment
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Phosphatidylcholine, with choline as polar head group, is another glycerophospholipid. It is a common membrane lipid. Phosphatidylinositol, with inositol as polar head group, is one glycerophospholipid. In addition to being a membrane lipid, phosphatidylinositol has roles in cell signaling. Sphingolipids are derivatives of the lipid sphingosine, which has a long hydrocarbon tail, and a polar domain that includes an amino group.
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Sterols Have 4 fused rings Cholesterol is the major sterol in vertebrates Steroid Hormones –Testosterone, Estrogen
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Cholesterol is largely hydrophobic. But it has one polar group, a hydroxyl, making it amphipathic. Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail.
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Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids. The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups.
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Cholesterol Important cell component – animal cell membranes – precursor of all other steroids including vertebrate sex hormones – high levels in blood may contribute to cardiovascular disease
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Cholesterol helps keep cell membranes fluid & flexible Important component of cell membrane
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From Cholesterol Sex Hormones What a big difference a few atoms can make!
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Working with Lipids Lipid Extraction Adsorption Chromatography Gas Liquid Chromatography Specific Hydrolysis Mass Spectrometry
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