Lipids

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

    1. 1. Chapter 21: Lipids Chem 104 K. Dunlap
    2. 2. 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
    3. 3. 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
    4. 4. 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
    5. 5. Energy & storage Lipids • Fatty Acids • Triacylgerols • Waxes
    6. 6. 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
    7. 7. 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
    8. 8. Cis, Trans, & Saturated Fatty Acids
    9. 9. Common Fatty Acids
    10. 10. 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
    11. 11. 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.
    12. 12. Triacylglycerols: stored fat • Insulation - seals, walruses, penguins • Energy – Hibernation 13
    13. 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.
    14. 14. 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
    15. 15. 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.
    16. 16. Complex Lipids • Figure 21.1 Schematic diagram of simple and complex lipids.
    17. 17. 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).
    18. 18. Lipids in Membranes: Fluid Mosaic Model • Polar heads and nonpolar tails
    19. 19. Storage vs. Structural lipids in membranes 20
    20. 20. Glycerophospholipids • Polar or charged group is attached to the third carbon of glycerol – Basis for nomenclature • Most abundant lipid in biological membranes 21
    21. 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
    22. 22. Glycosphingolipids: determinants of the blood groups 23
    23. 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.
    24. 24. Steroids • Steroids: a group of plant and animal lipids that have this tetracyclic ring structure.
    25. 25. 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
    26. 26. 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.
    27. 27. Lipoproteins • Cholesterol, along with fats, are transported by lipoproteins
    28. 28. Lipoproteins • Figure 21.5 Schematic of a low-density lipoprotein.
    29. 29. 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
    30. 30. 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
    31. 31. 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
    32. 32. Omega-3 Fatty Acids Eicosapentaenoic acid (20:5ω-3)
    33. 33. 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.
    34. 34. 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
    35. 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
    36. 36. 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
    37. 37. 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
    38. 38. 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?
    39. 39. This membrane lipid is classified as a ____________?
    40. 40. 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?
    41. 41. What are some important biochemical roles of lipids in Alaska?

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