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Nov 20 Lecture - Lipids - Lecture Notes - LIFESCI 2N03

10 Pages

Life Sciences
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Danny M.Pincivero

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LECTURE 6 LIFESCI 2N03 Lipids November 7, 11, 13, 14 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)  Types of fatty acids 1 LECTURE 6 LIFESCI 2N03 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  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  Double bonds at 6 and 9 carbons, respectively  Eg/ Linolenic Acid (18:3) – flaxseed oil, very thin oil  Omega-3, -6, -9 fatty acid  Dietary fatty acids – Omega (w) at C3 end; w1, w2, w3  once it reaches double bond, w# fatty acid; eg 4 C before double bond is w4  Geometric Shapes of Fatty Acids o Determined by the double bond o Cis form (bent) – most common – two lone hydrogen’s on the same side, causes bend in overall shape of hydrocarbon o Trans form (straight) – the more straight, the more solid at room temperature – two hydrogen’s on opposite sides of double bond  Produced during food preparation (eg/deep frying, hydrogenating oils (margarine) to add hydrogen’s to fatty acid; change cis to trans)  Related to cardiovascular disease; more so than saturated fats  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) – monounsaturated after the 9 C; body desaturated stearic acid (18:0)  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)  To transform fatty acids that are ingested– i) make longer ii) desaturation o Eicosanoids  Regulates various physiological functions (>20 carbons)  Taken up in neurons, retina of eye  Manufactured in the liver  Omega-3 fatty acids are beneficial  Improvement in markers that indicate cardiovascular disease (reduction in cholesterol, development and progression of certain cancers (breast, prostate) o Omega-3 Fatty Acid  Linolenic acid  18:3 2 LECTURE 6 LIFESCI 2N03  Flaxseed oil (1 tbps7.25g), walnuts (1 tbsp, 2.56g), flaxseeds (1 tbsp, 2.35 g)  ALA – alpha linolenic acid  Elongated (in liver) and desaturated to form 2 other FA’s  Elcosapantaenoic acid (EPA) – 20:5  Doxohexaenoic acid (DHA) – 22:6  EPA and DHA have strongest connections with reductions in cardiovascular disease risk; correlation with decreased breast and prostate cancer risk  Body only 5% efficient in using ALA to form EPA and DHA  need to ingest in diet as well  Food sources – fish (salmon, mackerel, sardines), shrimp  Farm salmon – if farmers do not feed salmon fatty acids, fish will not contain FA  Physiological effects –promotes blood vessel dilation (relaxation of smooth muscle), blood pressure decreases, decreases blood clotting, decreases inflammation; reduces CV disease risk o Omega-6 Fatty Acid  Linoleic Acid 18:2 (elongates and desaturated into arachidonic acid)  Arachidonic Acid (20:4) – precursor of prostaglandins (invaginates into injured tissue)  Function – blood vessel constriction, promotes blood clotting, inflammation, thrombosis, platelet aggregation  Food sources – cooking oils (sunflower, soybean, safflower), egg yolks, organ meats o Overall view  Ingest ALA – liver only 5% efficient at pathway; 5-15% of ALA converted to EPA and DHA  EPA – cardiovascular benefits  DHA – brain, neuron, eye development; infants, children  No pathway to go from LA to ALA  LA  ARA – can be made into prostaglandins; liver cells convert it to other fatty acids  DPA – counter part of omega-6; not shown to have benefits such as omega-3 o Essential Fat Sources:  Omega-3 FA 3 LECTURE 6 LIFESCI 2N03  -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)  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 (intensity, duration), glucose availability, blood insulin levels  Infants – required fat intake for development and growth of nervous system and cell membranes 2. Insulation/Protection  Visceral Fat – protects visceral organs (padding)  Visceral - Adipose tissue; stores a lot of triglycerides  Subcutaneous Fat – insulation barrier, reduces heat transfer  Adipose tissue found underneath skin  Content of visceral fat is considered to be a bigger risk factor for cardiovascular diseases  When visceral fat breaks down, it enters the hepatic portal circulation – excessive amounts of visceral fat to the liver (more moves through the liver, more gets stored in the liver  fatty liver; impairs glucose handling)  It is possible to have too little fat  Anorexia Nervosa – eating disorder, prolonged decrease in appetite and refusal to eat; starvation; body begins to induce fat and muscle tissue breakdown  Less severe forms  Amenorrhea – less severe forms of energy imbalance; lack of menses, exacerbated by high volume exercise (referred to as athletic induced amenorrhea); often in high endurance runners  Female athletes triad – amenorrhea, eating disorder, could lead to osteoporosis (skeletal problems); trying to keep body weight down to make running easier  Infertility problems in women due to deficiency of fats 3. Improves bioavailability and transport of other fat-soluble nutrients  Vitamin A, D, E, K – must form other complexes to be transported in the body  Phytochemicals – plant based chemicals that have a variety of health benefits  Carotenoids  Lycopene – predominant phytochemical in tomatoes; serving tomatoes with olive oil (monounsaturated fats) 4. Flavor, texture, odor of foods  Sensory stimulation  Moistens baked food items; also adds lots of energy  Energy content of a Tim Horton’s 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 (fatty acid; away from aqueous part) and hydrophilic (phosphate group; toward aqueous part)  Functions 1. Cell Membrane Structure – provides fluidity, makes the membrane “functional”; hence the label “fluid mosaic model” 2. Lipid Transport – component of bile; assists with fat emulsion; outer shell of chylomicrons and lipoproteins  Chylomicrons and lipoproteins – both lipoproteins; chylomicrons are larger; both carry cholesterol and triglycerides  Food Sources o Egg yolks, soybeans, peanuts o Not essential, body can produce its own phospholipids Sterols  Cholesterol (C27 45) – animal based sterol  Plant sterols – different effect than cholesterol  Ring structure, hydrophobic, lipophilic  Contains no fatty acid 4 LECTURE 6 LIFESCI 2N03  Importance of Cholesterol 1. Component of cell membranes (neurons)  Too low cholesterol  Stroke, lung, liver and behavioural problems (behavioural problems leads directly to the development of neurons)  Decreased immunity  AIDS – decreasing cholesterol indicates disease worsening 2. Precursor of molecules  Vitamin D  Hormones (cholesterol derivatives): o Progestins – progesterone, healthy pregnancy o Glucocorticoids – cortisol; forms liver glycogen, fat and protein breakdown o Mineralocorticoids – aldosterone, Na reabsorption in kidney, blood pressure regulation o Androgens – testosterone; male sex characteristics o Estrogens – female sex characteristics  Cholesterol Synthesis o All cells synthesize cholesterol o 1000 mg/day o Example:  Cells in eye lens – prevents cataracts  Brain – synthesizes cholesterol during development; (cholesterol for neurons)  Food Items o Animal origin only for cholesterol o Plants contain phytosterols (plant sterols, similar structure to cholesterol; different effect on body)  Poorly absorbeded, but decreases absorption of cholesterol – considered to be healthy  Used as a cholesterol-reducing food ingredient o Cholesterol containing food items  Recommended daily value for cholesterol: <300 mg  Examples:  1 tbsp butter – 31 mg  1 large egg – 219 mg  3 oz beef – 90 mg  3 oz beef liver – 330 mg  3 oz beef brain – 1,420 mg  DO NOT EAT POLAR BEAR LIVER – excess Vitamin A; acutely toxic, fatal  Cholesterol Absorption o Lower bioavailability than FA o Increases with increased dietary lipids o Decreases with increased dietary plant-derived food (due to fiber content)  Phytosterols interfere with body’s ability to absorb cholesterol Absorption  Duodenum and Jej
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