Lipids
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  • -9 kcal/ gram as opposed to 4 <br />
  • 1) Derivatives of fatty acids <br />
  • Highly reduced <br />
  • Most naturally occuring in cis configuration. Trans produced in rumen by fermentation so in dairy products and meat. Or by hydrogenation <br /> Trans or saturated more stable because steric hindrance is minimized <br /> Oxidative cleavage of double bond causes racidity <br />
  • Adipocytes in vertiebrates store large amounts of triglycerides. <br /> Stored as oil in seeds for energy for plants <br /> Lipases catalyze the release of FA from Triglycerides <br />
  • Double layer of lipids <br /> amphipathic <br />
  • Phospholipids have polar head group attached with phosphodiester linkage <br /> Some sphingolipids lack phosphate but have sugar <br /> Great diversity by different arrangements of nonpolar tails and polar heads <br />
  • glycerol-based phospholipids <br /> Derivatives of phosphatidic acid (parent compound) <br />
  • Biological role as enigmatic as a sphinx <br /> Over 60 different sphingolipids in humans <br /> Phosphodiester linkage in some cases and glycosidic linkage in others <br /> Sphingosine instead of glycerol (long chain amino alcohol) <br /> Differ in the polar head group attached to C-1 <br /> Ceramide is the parent molecule <br /> Sphingomyelin classified as a phospholipid because of phosphocholine side chain <br /> Myelin is membranous sheath surrounds and insulates axons of some neurons <br /> Glycosphingolipids have head groups with one or more sugar… subclasses of this are: <br /> Cerebrosides – sugar linked to ceramide, if galactose it is heavy in neural tissue, glucose prominent in non-neural tissues <br /> Globoside have 2 sugar or more sugars <br /> Gangliosides have oligosaccharides as polar group and a sialic acid giving it a negative charge <br /> Cerebrosides and globosides are collectively known as glycosphingolipids. <br /> Associated with multiple sclerosis <br /> Johann Thudichum discovered sphingolipids in 1874 named after the sphinx <br />
  • Cerebrosides and globosides are collectively known as glycosphingolipids. <br /> Carbohydrate moieties of sphingolipids define blood type <br />
  • Major sterol in animal tissue <br /> Bile acids are polar derivatives act as detergents and emulsify fats <br />
  • Paracrine act only on cells near the point of hormone synthesis <br /> Steroids and nonsteroidal antiinflammatory drugs inhibit <br /> CAMP is 3, 5 cyclic AMP  intracellular messenger <br /> Leukotrienes- induces contraction of the muscle lining to airways to lungs  target of prednisone <br /> Some prostaglandins effect smooth muscle contraction like in uterus in menstration and labor <br /> Effect blood floow <br /> regulate the production of acid and mucus in the stomach, and assist kidney functions <br />

Lipids Lipids Presentation Transcript

  • Chapter 21: Lipids Chem 104 K. Dunlap
  • Lipids • like CHO, lipids are compose of carbon, hydrogen and oxygen • unlike, CHO they do not contain multiple hydroxyl groups for hydrogen bonding, and therefore are insoluble in water • Lipids include a large variety of molecules: - fatty acids - triglycerides - waxes - eicosanoids - steroids - fat soluble vitamins
  • General info on Lipids… • insoluble in water • wide range of functions: insulate and protect internal organs, signaling molecules, energy • most efficient form in which energy is stored in the body • fats in animals absorb and sequester nonpolar contaminants, such as DDT, PCBs, organomercury •excess glucose, lipids and proteins are stored in adipose cells View slide
  • Lipids: diverse class of molecules 1) Energy and storage – fatty acids, triacylglycerides, waxes 2) Membrane structure – phospholipids, glycolypids, sterols 3) Signaling, cofactors and pigments – Eicosanoids, sterols, fat soluble vitamins View slide
  • Energy & storage Lipids • Fatty Acids • Triacylgerols • Waxes
  • Fatty Acids • long chain, even number carboxylic acids, typically between 12 and 26 carbons • Saturated fatty acids have no double bonds • Unsaturated fatty acids have at least one double bond
  • Unsaturated Fatty Acids • Most naturally occurring fatty acids are in the cis form • causes a bend in the molecule • chains cannot pack tightly, and therefore are less dense, with lower melting points
  • Cis, Trans, & Saturated Fatty Acids
  • Common Fatty Acids
  • Formation of Triglycerides • glycerol backbone, with three fatty acids, joined by ester linkages • The fatty acids that compose the triglyceride affect their properties, such as melting point • Fats have FAs with fewer double bonds • Oils have FAs with more double bonds
  • Triglycerides • The lower melting points of triglycerides rich in unsaturated fatty acids are related to differences in their three-dimensional shape. – Hydrocarbon chains of saturated fatty acids can lie parallel with strong London dispersion forces between their chains; they pack into well-ordered forms and melt above room temperature – Because of the cis configuration of the double bonds in unsaturated fatty acids, their hydrocarbon chains have a less ordered structure and London dispersion forces between them are weaker; these triglycerides have melting points below room temperature.
  • Triacylglycerols: stored fat • Insulation - seals, walruses, penguins • Energy – Hibernation 13
  • Hydrogenation • Hardening: reduction of some or all of the carbon-carbon double bonds of an unsaturated triglyceride using H2/metal catalyst. – In practice, the degree of hardening is carefully controlled to produce fats of a desired consistency. – The resulting fats are sold for kitchen use (Crisco, Spry, Dexo, and others). – Margarine and other butter substitutes are produced by partial hydrogenation of polyunsaturated oils derived from corn, cottonseed, peanut, and soybean oils.
  • Hydrogenation of Unsaturated Fats • Oils can be converted to semi-solids through hydrogenation that converts the double bonds to single bonds • In the process, some double bonds are converted to trans form
  • Complex Lipids • Phospholipids – contain an alcohol, two fatty acids, and a phosphate ester. – In glycerophospholipids, the alcohol is glycerol. – In sphingolipids, the alcohol is sphingosine. • Glycolipids – Complex lipids that contain a carbohydrate.
  • Complex Lipids • Figure 21.1 Schematic diagram of simple and complex lipids.
  • Membranes • Complex lipids form the membranes around cells and small structures within cells. • In aqueous solution, complex lipids spontaneously form into a lipid bilayer, with a back-to-back arrangement of lipid monolayers. – Polar (hydrophilic) head groups are in contact with the aqueous environment. – Nonpolar (hydrophobic) tails are buried within the bilayer – The arrangement of hydrocarbon tails in the interior can be rigid (if rich in saturated fatty acids) or fluid (if rich in unsaturated fatty acids).
  • Lipids in Membranes: Fluid Mosaic Model • Polar heads and nonpolar tails
  • Storage vs. Structural lipids in membranes 20
  • Glycerophospholipids • Polar or charged group is attached to the third carbon of glycerol – Basis for nomenclature • Most abundant lipid in biological membranes 21
  • Sphingolipids • One fatty acid joined to sphingosine • Polar head group • Sphingomyelin, Glycosphingolipids, Gangliosides • Sphingomyelin - animal cells, especially myelin • Some involved in signal transduction & cell surface recognition 22
  • Glycosphingolipids: determinants of the blood groups 23
  • Cholesterol • Cholesterol is the major sterol in animal tissues – It is a component in plasma membranes in all animal cells. – It is the precursor of all steroid hormones, some vitamins and bile acids.
  • Steroids • Steroids: a group of plant and animal lipids that have this tetracyclic ring structure.
  • Steroids • cholesterol, bile acids, vitamin D, and many hormones • Oxidized sterols • Lipid soluble and enter cells • Bind nuclear receptors and alter gene expression and metabolism
  • Cholesterol • Cholesterol is the most abundant steroid in the human body, and also the most important. – It is a component in plasma membranes in all animal cells. – It is the precursor of all steroid hormones and bile acids.
  • Lipoproteins • Cholesterol, along with fats, are transported by lipoproteins
  • Lipoproteins • Figure 21.5 Schematic of a low-density lipoprotein.
  • Cholesterol •is the most abundant steroid and is the starting material for all other steroids • present in animal fats • major factor in the development of atherosclerosis • transported by lipoproteins: VLDL (very low density lipoproteins)- transport triglycerides LDL (low density lipoproteins)- transport cholesterol from liver to tissues HDL (high density lipoproteins)- transport cholesterol from tissues to the liver for elimination
  • Bile Salts • Bile salts, the oxidation products of salts cholesterol. – synthesized in the liver, stored in the gallbladder, and secreted into the intestine where they emulsify dietary fats and aid in their absorption and digestion
  • Fats Essential Fatty acids: Omega-3 EPA, DHA, linoleic • recommended 30% of diet -10% monounsaturated -10% saturated -10% unsaturated Omega-6 Arachidonic acid, α-linolenic • EPA, DHA, AA are 20 carbon hormone-like fatty acids that play an important part in the immune function
  • Omega-3 Fatty Acids Eicosapentaenoic acid (20:5ω-3)
  • Prostaglandins & Leukotriene • are not stored in tissues as such, but are synthesized from membrane-bound 20-carbon polyunsaturated fatty acids in response to specific physiological triggers. – One such polyunsaturated fatty acid is arachidonic acid.
  • Eicosanoids: paracrine hormones Regulate synthesis of cAMP production  fever, pain, blood flow, and uterine contraction Produced by platelets, important in clotting and blood flow Inflammation, asthma, allergy • Derived from the 20 carbon polyunsaturated fatty acid (arachidonic acid) • Involved in reproduction, inflammation, fever and pain • 3 classes: Prostaglandins, thromboxanes, leukotrienes 35
  • Phospholipid membrane Phospholipase A2 O HO Eicosapentaenoic acid Arachidonic Cyclooxygenases (COX) Prostaglandins (PG) & Thromboxanes (TX) Lipoxygenases (LOX) Leukotrienes -poor substrate for cyclooxygenases -gives rise to series 5 leukotrienes
  • More on Lipids…… • fats insulate and protect internal organs • most efficient form in which energy is stored in the body -9 kcal/ gram as opposed to 4 • fats in animals absorb and sequester nonpolar contaminants, such as DDT, PCBs, organomercury • excess glucose, lipids and proteins are stored in adipose cells
  • Endocrine Disruptors •Hormones are substances produced in specialized glands such as the pituitary, thymus, hypothalamus, thyroid, adrenals, pancreas, gonads which make up the endocrine system • direct and control reproduction, prenatal development, growth, and many regulatory processes • endocrine disruptors refer to contaminants that mimic or interfere with the function of hormones: PCB, dioxin, DDT
  • 1. What is a polyunsaturated fatty acid? 2. What happens when a polyunsaturated FA is hydrogenated? What happens to the physical properties of the oils? 3. What molecules react to form a triglyceride? 4. What is an endocrine disruptor?
  • This membrane lipid is classified as a ____________?
  • 5. In contrast to water-soluble vitamins, which must be part of our daily diet, fat-soluble vitamins can be stored in the body in amounts sufficient for many months. Suggest an explanation for this difference. 6. The melting points of a series of 18-carbon fatty acids are: stearic acid, 69.6 C°; oleic acid, 13.4 C°; linoleic acid, -5 C°; and linolenic acid, -11 °C. What structural aspect of these 18-carbon fatty acids can be correlated with the melting point?
  • What are some important biochemical roles of lipids in Alaska?