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Nov 7 - Lipids - Lecture Notes - LIFESCI 2N03

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McMaster University
Life Sciences
Danny M.Pincivero

LECTURE 6 LIFESCI 2N03 Lipids November 7, 2013 Lipids  Broad range of organic molecules that dissolve easily in organic solvents, but much less soluble in water  Classification – different degrees of solubility 1. Hydrophobic (water fearing) – do not dissolve in water; will coalesce in water 2. Lipophilic (fat loving) – dissolve into cells without the need of a transporter; get lipids out of digestive system using concentration gradient (pure lipid (as opposed to with carbs or proteins)= easy passage from digestive to cardiovascular system)  Main Classes of Lipids 1. Triglycerides (also called triacylglycerol’s)  Largest category, makes up most lipids  Plant and animal origin  3 fatty acids connected to backbone  Storage form of fatty acids in body  Lipases act on triglycerides when stimulated by glucagon or epinephrine to break down triglycerides (break off acids from glycerol) 2. Phospholipids  Makes up approximately 2% of all dietary lipids  Plant and animal sources  Soluble in fat and water  Major constituent of cell membranes  Involved in fatty acid transport (forms outer shell of chylomicrons and lipoproteins) 3. Sterols  Small percentage (<2%) of lipids in diet  Most famous  Cholesterol  Cells make cholesterol  Precursor to hormones (sex and cortisol), Vitamin D and bile acids Fatty Acids  Most abundant lipid in diet; storage form of lipids in body; lipid used for energetic purposes  Using fatty acids for energy – Beta-oxidation  Hydrocarbon chain (4-24 carbons) o Short Chain <6 carbons o Medium Chain 6-10 carbons o Long Chain >12 carbons  Fatty Acid Notation (# of C:# double bonds) eg/ 18:0 = 18 carbons, 0 double bonds; 0 = saturated o Eg/ Butyric Acid 4:0 (provides flavour in butter) o Eg/ Palmitic Acid 16:0 o Eg/ Stearic Acid 18:0 (chocolate, meat fats, solid at room temperature)  Effect of Chain Length o Longer Chain = more solid at room temperature o Shorter Chain = more liquid at room temperature (oils) 1 LECTURE 6 LIFESCI 2N03  Types of fatty acids 1. Saturated – all carbons are single bonded to adjacent carbons or 2 hydrogen atoms 2. Monosaturated – 1 double bond – tends to be more beneficial than polyunsaturated eg/olive oil 3. Polyunsaturated fatty acid (PUFA) – >1 double bonds  Omega (w) at CH 3nd; w1, w2, w3  once it reaches double bond, w# fatty acid; eg 4 C before double bond is w4  Eg/ Oleic Acid (18:1) – olive oil (thick) at room temperature; may solidify with refrigeration; omega-9 FA  Eg/ Linoleic acid (18:2) – soybean oil, omega-6 and omega-9 fatty acids o Double bonds at 6 and 9 carbons, respectively  Eg/ Linolenic Acid (18:3) – flaxseed oil, very thin oil o Omega-3, -6, -9 fatty acid  Geometric Shapes of Fatty Acids o Determined by the double bond o Cis form (bent) – most common o Trans form (straight) – the more straight, the more solid at room temperature  Produced during food preparation (eg/deep frying, hydrogenating oils (margarine) to add hydrogen’s to fatty acid, )  Related to cardiovascular disease  Non-Essential Fatty Acid o Fatty acids our bodies can manufacture o Carbons added to short-chain fatty acids by liver (elongation) o Done mainly for structural fatty acids (membranes and myelin) o Fatty acids in breast milk o Eg/ Oleic Acid (omega-9) – body desaturated stearic acid  Essential Fatty acid o No enzymes to desaturate before omega-9 carbon – therefore, omega-3 and omega-6 fatty acids are essential o Omega-3 and-6 fatty acids are needed – used to make other fatty acids (eicosanoids) 2 LECTURE 6 LIFESCI 2N03 o Eicosanoids  Regulates various physiological functions (>20 carbons)  Manufactured in the liver  Ooemga-3 fatty acids are beneficial o Omega-3 Fatty Acid  Linolenic acid  18:3  Flaxseed oil, walnuts, flaxseeds  Elongated (in liver) and desaturated to form 2 other FA’s  Elcosapantaenoic acid (EPA) –  Doxohexaenoic acid (DHA) –  Food sources – fish  Physiological effects –promotes blood vessel dilation, decreases blood clotting, decreases inflammation o Omega-6 Fatty Acid  Linoleic Acid 18:2  Arachidonic Acid (20:4) – precursor of prostaglandins  Function – blood vessel constriction, promotes blood clotting, inflammation, thrombosis, platelet aggregation  Food sources – cooking oils (sunflower, soybean, safflower), egg yolks, organ meats o Essential Fat Sources:  Omega-3 FA  -linolenic flax seed oil, walnuts, flaxseeds  DHA, EPA fish (Atlantic cod, haddock, salmon), human milk  Omega-6 FA  Linoleic acid plants, soybean and canola oils  Omega-9 FA  Olive oil o Recommended 2:1 ratio of omega-6 to omega-3  Typical North American diet has much higher ratio (~30:1) 3 LECTURE 6 LIFESCI 2N03  Food processing contributes to increased ratio – omega-3’s are removed to reduce rancidity (prolong shelf life)  Target ratio = 1:1 to1:4 (omega 6 to omega 3)  Triclygyceride Functions 1. Energy Source  Depends on physical activity level, glucose availability, blood insulin levels  Infants – required fat intake 2. Insulation/Protection  Visceral Fat:  Subcutaneous Fat:  Can we have too little fat? Yes  Anorexia Nervosa – eating disorder, prolonged decrease in appetite and refusal to eat; starvation  Amenorrhea – less severe forms of energy imbalance; lack of menses, exacerbated by high volumte exercise (referred to as athletic induced amenorrhea)  Female athletes triad – amenorrhea, eating disorder, osteoporosis  Infertility problems in women 3. Improves bioavailability and transport of other fat-soluble nutrients  Vitamin A, D, E, K  Phytochemicals (carotenoids, lycopene); serving tomatoes with olive oil 4. Flavor, texture, odor of foods  Sensory stimulation  Moistens baked food items; also adds lots of energy  Energy content of a Tim Hortons muffin? Phospholipids  Similar to triglycerides; contains glycerol and fatty acids  Typically, one glycerol; 2 FA’s and a phosphate (+ nitrogen); makes the whole molecule hydrophobic and hydrophilic  Functions 1. Cell Membrane Structure – provides fluidity, makes the membrane
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