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Chapter 10: Lipids

Lipids. One of 4 major classes of compounds found in living tissueNucleic acids, proteins, carbohydrates, lipidsOils, fats, or fat-like materialSome vitamins, hormonesNot polymericAggregateStructural matrix of biological membranesStructural varietyLargely hydrophobicInsoluble in waterSolub

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Chapter 10: Lipids

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    1. Chapter 10: Lipids Dr. Clower Chem 4202

    2. Lipids One of 4 major classes of compounds found in living tissue Nucleic acids, proteins, carbohydrates, lipids Oils, fats, or fat-like material Some vitamins, hormones Not polymeric Aggregate Structural matrix of biological membranes Structural variety Largely hydrophobic Insoluble in water Soluble in organic solvents (chloroform, ether)

    3. Outline Storage Fatty acids Triacylglycerols Structural Phospholipids Glycolipids Sterols Other lipids Fat-soluble vitamins Eicosanoids

    4. Fatty Acids Simplest type; components of more complex lipids Carboxylic acids with long aliphatic hydrocarbon chains Generally 10-20 carbons Most common are 16, 18 Mostly even number due to synthesis Saturated or unsaturated

    5. Saturated Fatty Acids Only C-C Highly flexible Most stable conformation = fully extended mp increase with chain length ex: stearic acid (octadecanoic acid)

    6. Unsaturated Fatty Acids Contains C-C Can be polyunsaturated essential FAs First double bond typically at C9 D9 Double bonds every three carbons D9,12 -CH-CH-CH2-CH-CH-CH2- ex: oleic acid (18:1) and linoleic acid (18:2)

    7. Omega-3 Fatty Acids Corn, fish oil Reduce possibility of heart disease Don’t stick to walls of blood vessels Promote blood flow ex: linolenic acid

    8. Unsaturated Fatty Acids Double bonds Typically cis or trans? Causes bend in hydrocarbon chain Do not pack as well as saturated FAs mp decrease as unsaturation increases

    10. Triacylglycerols aka triacylglycerides Fatty acid triesters of glycerol Simple Mixed

    11. Triacylglycerols Most abundant class of lipids in animals mp determined by degree of unsaturation More unsaturation in plants than in animals Function = energy reserves, insulation Better source of E than carbohydrates Stored in adipocytes throughout the body Hydrolyzed by lipases as needed

    12. Fatty acids in food Triacylglycerols and free FAs Saturated = solid at rt Unsaturated = liquid at rt “Fat” = mostly saturated Animal sources (meat, butter) “Oil” = mostly unsaturated Plant sources (olive, peanut) Partial hydrogenation Raise mp (semi-solid) Soft margarine, etc. More sat fat but less cholesterol than butter Side effect = production of trans FAs Behave like saturated fat Increases LDL levels Decrease HDL levels

    13. Structural Lipids Amphipathic Hydrophobic chain(s) Hydrophilic (-OH or larger) Pack into bilayers Biological membranes

    14. Phospholipids Contain phosphodiester bond Negative charge at physiological pH Example: Glycerophospholipids aka phosphoglycerides Major component of membranes Esterified glycerol-3-phosphate Phosphoryl group linked to polar group (various structure)

    17. Structure of Glycerophospholipids Determined by analysis of products from enzyme-catalyzed hydrolysis Phospholipases Cleave specific bonds Enzymes are small Only section being cleaved fits in active site Remainder of lipid in non-aqueous environment or stabilized by nonpolar AA side chains

    18. Plasmalogens One type of glycerophospholipid C1 linkage is a,b-unsaturated ether (not ester) Heart tissue of vertebrates Membranes of some invertebrates and bacteria

    19. Glycolipids Monosaccharide or oligosaccharide at polar end Example: Galactolipids Galactose residues Glycosidic linkages to C3 of 1,2-diacylglycerol Plant cells Internal membranes of chloroplasts

    20. Sphingolipids Also major component of membranes Phospholipid or glycolipid (depends on polar group) Derivatives of sphingosine (instead of glycerol) C18 amino alcohol Ceramide Acylated amine Parent compound of most abundant sphingolipids

    22. Glycerophospholipids/Sphingolipids

    23. Sterols Sterol Four fused rings Greater rigidity than other membrane lipids One or more hydroxyl groups Gives amphipathic character Hydrocarbon side chain Length of C16 FA Cholesterol Most abundant sterol in animals Produced by liver; supplied by diet High levels lead to gallstones and deposits on arteries (plaque)

    24. Sterols Metabolic precursors of steroid hormones Regulate physiological functions Androgens (testosterone) Estrogens (b-estradiol) Glucocorticoids (cortisol) Insoluble in water Bind to proteins for transport to target tissue

    25. Vitamin D Sterol derivatives Open B rings Function Regulate Ca and P absorption during bone growth Sources Diet: D2 (milk additive, plant sources) and D3 (animal sources) Precursor: intermediate in cholesterol synthesis Formed in skin non-enzymatically from 7-dehydrocholesterol Deficiency Soft bones, impaired growth and skeletal deformities in children

    26. Other Lipids Classified on basis of physical properties Solubility Hydrophobicity Amphiphilicity Fat-soluble vitamins Vitamins A, E, K (and D) Isoprenoids Eicosanoids Prostaglandins Thromboxanes Leukotrienes

    27. Vitamin A Collective term for retinol, retinal, retinoic acid Formed from oxidative cleavage of b-carotene in liver Function Aldehyde: visual cycle/process, component of rhodopsin (visual pigment) Alcohol, carb acid: growth, reproduction Deficiency Night blindness Xerophthalmia Dryness in eyes No tear production Damage to cornea Leads to blindness

    28. Vitamin K Phylloquinone or menaquinone Function Synthesis of blood clotting proteins Sources K1 = plants; K2 = animals Bacteria in intestine Deficiency Unlikely due to synthesis and wide distribution in food Injection for infants Hemolytic anemia = destruction of red blood cells Toxicity Jaundice from large doses of vit. K, toxic effects on membrane of red blood cells, cells die, lead to increased levels of yellow bilirubin (formed from heme)

    29. Vitamin E a-tocopherol Function Antioxidant: prevents cell damage from oxidation of polyunsaturated FAs in membranes by O2 and free radicals Deficiency Associated with defective lipid transport/absorption

    30. Olestra Artificial, noncaloric fat substitute (indigestible) FDA warning “This Product Contains Olestra. Olestra may cause abdominal cramping and loose stools. Olestra inhibits the absorption of some vitamins and other nutrients. Vitamins A, D, E, and K have been added.”

    31. Eicosanoids Hormones involved in production of pain, fever, inflammatory reactions Prostaglandins Thromboxanes Leukotrienes Metabolites of arachidonic acid (a polyunsatruated FA) Synthesis inhibited by NSAIDs e.g. acetylsalicylic acid (aspirin) Acylate Ser residue, preventing access to active site

    32. Chapter 10 Problems 1-5, 8-10

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