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Lipids : What do you need to know?

Lipids : What do you need to know?. Classification of major lipid groups Structure of fatty acids Physical properties of fatty acids Structure & function of triacylglycerols Chemical reactions of triacylglycerols Compare phospholipids & glycolipids

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Lipids : What do you need to know?

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  1. Lipids: Whatdo you need to know? Classification of major lipid groups Structure of fatty acids Physical properties of fatty acids Structure & function of triacylglycerols Chemical reactions of triacylglycerols Compare phospholipids & glycolipids Composition & properties of membrane lipids Structure & function of cholesterol Compare & contrast 3 types of cellular membrane transport Compare & contrast some steroid hormones Structure & function of bile acids Compare & contrast 3 types of eicosanoids Structure & function of biological waxes Fats and oils are the most widely occurring types of lipids. Thick layers of fat help insulate polar bears against the effects of low temperatures.

  2. A lot of structural variety is represented by lipids. They are typically: - insoluble in H2O - soluble in NP solvents

  3. Lipid Categories (based on function) • Energy Storage • Triacylglycerols (fats) • Membrane structure • Phospholipids, Sphingoglycolipids, cholesterol • Emulsification • Bile acids • Messenger molecules • Steroid hormones; eicosanoids • Protective coating • Biological waxes

  4. Lipid Building Blocks -Fatty Acids (F.A.) • Fatty Acids = monocarboxylic acids • Straight chains • Long: C12-C26 • Medium: C8 & C10 • Short: C4 & C6 • Saturated (SFA) • Monounsaturated (MUFA) • Polyunsaturated (PUFA) • Usually </= 6 double bonds • Almost always known by common names

  5. All of these are 18 carbon chains

  6. Various formulas can be used to draw the long chains: e.g. 14 carbons long

  7. Structural Notation for F.A. • F.A. With 18 C atoms and 1 double bond (MUFA).

  8. Physical Properties • Water solubility decreases with increasing # C atoms • MP increases with increasing # C atoms • MP decreases with increasing unsaturation • Straight chains pack well • Bent chains don’t pack well Four 18-carbon fatty acids, which differ in the number of double bonds present.

  9. Compounds with double bonds, or rings: Observe attached groups lying above or below plane of double bond or ring. "cis" groups on same side. "trans" groups are across. Different isomers have different physical and sometimes different chemical properties. Quick review of cis/trans isomerism:

  10. If there is more than one double bond, they occur atthree-carbonintervals. -C=C-C-C=C- This is called thedivinylmethanepattern. Cis pattern creates bent molecules. This affects the intermolecular bonding

  11. Space-filling models of four 18-carbon fatty acids, which differ in the number of double bonds present. Note how the presence of double bonds changes the shape of the molecule.

  12. Common names derive from a common source of the compound or the source from which it was first isolated. e.g. Palmitic acid is found in palm oil Oleic acid - a major part of olive oil (oleum) Stearic (from Greek word for “solid”) acid is solid at room temperature. Spiders (Arachnids) contain arachidonic acid.

  13. InIUPAC system, carboxyl carbon is number one. All bonds reference the carboxyl carbon. e.g. a double bond between 9th and 10th C is at the 9-carbon + a Greek name cis-9- hexadecanoic acid (16 carbons) These names are awkwardly long so aren’t used as commonly as some of the other systems

  14. Essential fatty acids: alpha-linolenic acid(ALA, an omega-3) and linoleic acid(an omega-6) Human body needs, but cannot manufacture, them. When sufficient quantities are supplied in the diet, the body can make enough Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) to create the eicosanoids that form our metabolic "thermostat" system Also affect brain development and function. Lack of these can cause: Depression, ADHD, Alzheimers, & Inflammation

  15. Triacylglycerols = Triglycerides = Triesters Simple mixed Adipoctyes are the body’s triacylglycerol-storing cells.

  16. Triple esterificationreaction between glycerol and 3 molecules of stearic acid (18:0 fatty acid).Three molecules of waterare a by-product of this reaction. Dehydration synthesis (condensation rxn)of a simpleTriacylglycerol (triglyceride)

  17. Fats vs. Oils • Fats: typically are solids at room temp. • Mostly SFAs • Generally from animals Warm-blooded organisms Fluid at warmer temperatures • Oils: typically are liquids at room temp. • Lots of MUFAs and PUFAs • Generally from plants More kinks in the chain, the more fluid the oil. Makes cell membranes flexible and permeable, allowing nutrients in & waste products out.

  18. Lipids & your Diet • General population correlation • High triglyceride intake = increased risk of heart disease & certain cancers • But... Inuit...,etc. • “Good” vs. “Bad” fats • SFA = “Bad” • MUFA = “Good” cold water fish (-3 FA) • PUFA • -3 = “Good” • -6 = “Bad”

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