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Lipids. What are Lipids?. Class of biomolecules that are all water insoluble No defining characteristic except that all of them share the same trait: non-polar Most common are fatty acids and esters of fatty acids Functions Energy Storage Cell membrane Thermal blanket and cushion

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Lipids


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what are lipids
What are Lipids?
  • Class of biomolecules that are all water insoluble
  • No defining characteristic except that all of them share the same trait: non-polar
  • Most common are fatty acids and esters of fatty acids
  • Functions
    • Energy Storage
    • Cell membrane
    • Thermal blanket and cushion
    • Precursors of hormones
fatty acids
Fatty Acids
  • Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end.
  • A 16-C fatty acid: CH3(CH2)14-COO-

Non-polarpolar

  • General Structure:
fatty acids1
Fatty Acids
  • Double bonds in fatty acids usually have the cis configuration.
  • Most naturally occurring fatty acids have an even number of carbon atoms.
  • IUPAC naming:
    • COOH carbon as C1
    • Farthest carbon is ω
    • Total carbons/# double bonds/Δdoublebond position
fatty acids2
Fatty Acids
  • Some fatty acids and their common names:
    • 14:0myristic acid; 16:0 palmitic acid; 18:0 stearic acid;
    • 18:1 cisD9  oleic acid
    • 18:2 cisD9,12  linoleic acid
    • 18:3 cisD9,12,15a-linonenic acid
    • 20:4 cisD5,8,11,14arachidonic acid
    • 20:5 cisD5,8,11,14,17eicosapentaenoic acid (an omega-3)
  • Essential fatty acids
    • ALA- ω-3 FA precursor for EPA and DHA
    • LA – ω-6 FA precursor of AA
fatty acid chemistry
Fatty Acid Chemistry
  • Peroxidation
    • a non-enzymatic reaction catalyzed by oxygen
    • may occur in tissues or in foods (spoilage)
    • the hydroperoxide formed is very reactive and leads to the formation of free radicals which oxidize protein and/or DNA (causes aging and cancer)
    • principle is also used in drying oils (linseed, tung, walnut) to form hard films
drying oils application of peroxidation
Drying Oils: Application of Peroxidation
  • based on the ease of autoxidation and polymerization of oils (important in paints and varnishes)
  • the more unsaturation in the oil, the more likely the “drying” process
    • Non-drying oils:
      • Castor, olive, peanut, rapeseed oils
    • Semi-drying oils
      • Corn, sesame, cottonseed oils
    • Drying oils
      • Soybean, sunflower, hemp, linseed, tung, oiticica oils
fatty acid chemistry1
Fatty Acid Chemistry
  • Transesterification
    • Acid-catalyzed exchange betweein R groups of esters
    • Frequently-used in polyester, methanolysis and biodiesel industries
fatty acid chemistry2
Fatty Acid Chemistry
  • Hydrogenation
    • Reduces double bonds on unsaturated fatty acids
    • Prevents oils from going rancid
fatty acid chemistry3
Fatty Acid Chemistry
  • Saponification
    • Base hydrolysis of triglycerides to produce fatty acid salts
    • High saponification number, shorter chain length
soaps
Soaps
  • Types of soaps:
    • Sodium soap – ordinary hard soap
    • Potassium soap – soft soap (shaving soaps are potassium soaps of coconut and palm oils)
    • Castile soap – sodium soap of olive oil
    • Green soap – mixture of sodium and potassium linseed oil
    • Transparent soap – contains sucrose
    • Floating soap – contains air
    • Calcium and magnesium soaps are very poorly water soluble (hard water contains calcium and magnesium salts –these insolubilize soaps)
fatty acid chemistry4
Fatty Acid Chemistry
  • Iodine Number
    • measures the degree of unsaturation in a given amount of fat or oil
    • the iodine number is the number of grams of iodine absorbed by 100 grams of fat
      • Cottonseed oil: 103 –111
      • Olive oil: 79 – 88
      • Linseed oil: 175 –202
    • frequently used to determine adulteration of commercial lots of oils
fatty acid chemistry5
Fatty Acid Chemistry
  • Acetyl Number
    • the number of milligrams of KOH needed to neutralize the acetic acid of 1 g of acetylated fat
fatty acid chemistry6
Fatty Acid Chemistry
  • Reichert-Meisl Number
    • measures the amount of volatile fatty acids (low MW and water soluble Fas)
    • the R-M number is the number of milliliters of 0.1N alkali required to neutralize the soluble fatty acids distilled from 5 Gm of fat
    • butter fat has a high R-M number
    • Indicator of non-fat compounds in edible fats, or volatile fatty acids
fats and oils
Fats and Oils
  • fats are solids or semi solids
  • oils are liquids
  • melting points and boiling points are not usually sharp (most fats/oils are mixtures)
  • when shaken with water, oils tend to emulsify
  • pure fats and oils are colorless and odorless (color and odor is always a result of contaminants) – i.e. butter (bacteria give flavor, carotene gives color)
waxes
Waxes
  • simple esters of fatty acids (usually saturated with long chain monohydric alcohols)
    • Beeswax – also includes some free alcohol and fatty acids
    • Spermaceti – contains cetylpalmitate (from whale oil) –useful for pharmaceuticals (creams/ointments; tableting and granulation)
    • Carnauba wax – from a palm tree from brazil – a hard wax used on cars and boats
slide20

Spermaceti source

Carnauba wax source

Bee’s wax

glycerides
Glycerides
  • Function
    • Storage of energy
    • Cushions
triglycerides
Triglycerides
  • Esters of fatty acids and glycerol
  • Constituent of fats and oils
phosphoglycerides
Phosphoglycerides
  • aka glycerophospholipids
  • Major constituent of cell membranes
  • Structure
    • Glycerol backbone with esterifies fatty acids at C1 and C2
    • Fatty acids are usually non-identical
    • Phosphate group attached to C1
    • A polar group is usually esterified to Pi (usually serine, choline, ethanolamine, glycerol, or inositol
phosphoglycerides1
Phosphoglycerides
  • Structure=Function
    • Polar region – glycerol, phosphate group, X
    • Nonpolar region – fatty acid
    • Amphiphatic character
    • Ideal for forming bilayers
phosphatidyl inositol
Phosphatidyl inositol
  • Inositol as a polar head group
  • Has roles in cell signaling as well as a cell membrane component
ether glycerophospholipids
Ether glycerophospholipids
  • Possess an ether linkage instead of an acyl group at the C-1 position of glycerol
    • PAF ( platelet activating factor) - a potent mediator in inflammation, allergic response and in shock (also responsible for asthma-like symptom
    • The ether linkage is stable in either acid or base
  • Plasmalogens: cisa,b-unsaturated ethers
    • The alpha/beta unsaturated ether can be hydrolyzed more easily
sphingolipids
Sphingolipids
  • derivatives of the lipid sphingosine, which has a long hydrocarbon tail, and a polar domain that includes an amino group
  • Like phosphoglycerides, are also constituents of cell membranes
  • Can be reversibly phosphorylated and utilized as signaling molecule
sphingolipid derivatives
Sphingolipid Derivatives
  • Ceramide- amino group of sphingosineforms an amide bond with a fatty acid carboxyl
  • Sphingomyelinhas a phosphocholine or phosphethanolamine head group.
    • common constituent of plasma membranes
    • similar in size and shape to the glycerophospholipidphosphatidyl choline
sphingolipid derivatives1
Sphingolipid Derivatives
  • Cerebrosidea sphingolipid (ceramide) with a monosaccharide such as glucose or galactose as polar head group.
  • Ganglioside– a ceramide with polar head group that is a complex oligosaccharide, including the acidic sugar derivative sialicacid
  • Both are collectively known as glycosphingolipidsand are commonly found on the outer leaflet of the cell membrane
ganglioside
Ganglioside
  • Cerebrosides
      • One sugar molecule
        • Galactocerebroside – in neuronal membranes
        • Glucocerebrosides – elsewhere in the body
  • Sulfatides or sulfogalactocerebrosides
      • A sulfuric acid ester of galactocerebroside
  • Globosides: ceramide oligosaccharides
      • Lactosylceramide
        • 2 sugars ( eg. lactose)
  • Gangliosides
      • Have a more complex oligosaccharide attached
      • Biological functions: cell-cell recognition; receptors for hormones
cardiolipids
Cardiolipids
  • A polyglycerol phospholipid; makes up 15% of total lipid-phosphorus content of the myocardium – associated with the cell membrane
  • Cardiolipids are antigenic and as such are used in serologic test for syphilis (Wasserman test)
sulfolipids
Sulfolipids
  • also called sulfatides or cerebroside sulfates
  • contained in brain lipids
  • sulfate esters of cerebrosides
  • present in low levels in liver, lung, kidney, spleen, skeletal muscle and heart
  • function is not established
lipid storage diease
Lipid Storage Diease
  • a group of inherited metabolic disorders in which harmful amounts of fatty materials (lipids) accumulate in various tissues and cells in the body
  • also known as sphingolipidoses
  • genetically acquired
  • due to the deficiency or absence of a catabolic enzyme
    • Tay Sachs disease
    • Gaucher’s disease
    • Niemann-Pick disease
    • Fabry’s disease
cholesterol
Cholesterol
  • an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail.
    • serves as a component of membranes of cells (increases or moderates membrane fluidity)
    • precursor to steroid hormones and bile acids
    • storage and transport –cholesterol esters
  • Cholesterol is largely hydrophobic.
  • But it has one polar group, a hydroxyl, making it amphipathic.
eicosanoids
Eicosanoids
  • Includes prostaglandins and related compounds
  • Derivatives of arachidonic acid
  • Serves as local hormones and intercellular signaling
  • Key hormones in inflammation response
eicosanoids1
Eicosanoids
  • Types of Eicosanoids
    • Prostaglandins
    • Prostacyclins
    • Thromboxanes
    • Leukotrienes
    • epoxyeicosatrienoicacids.
  • Biological Functions
    • Inflammation
    • Fever
    • regulation of blood pressure
    • blood clotting
    • immune system modulation
    • control of reproductive processes and tissue growth
    • regulation of the sleep/wake cycle
terpenes
Terpenes
  • simple lipids, but lack fatty acid component
  • formed by the combination of 2 or more molecules of 2-methyl-1,3-butadiene (isoprene)
  • monoterpene (C-10) – made up of 2 isoprene units
  • sesquiterpene (C-15) – made up of 3 isoprene units
  • diterpene (C-20) – made up of 4 isoprene units
terpenes1
Terpenes
  • tetraterpenes (C-40) are not as common as mono, di, and triterpenes
    • include the carotenoids such as beta-carotene (precursor of vitamin A) and lycopene found in tomatoes
    • usually colorful compounds due to highly conjugated system
  • polyisoprenoids or polyprenols consist of numerous isoprene adducts (8 – 22)
    • examples include dolichol phosphate, undecaprenyl alcohol (bactoprenol) and the side chains of vitamins K, vitamin E and coenzyme Q
lipid linked proteins
Lipid-linked proteins
  • Proteins that have lipids covalently bonded to them
  • Usually found in cell membranes
  • 3 types are most common:
    • Prenylated proteins
      • Farnesylated proteins (C15 isoprene unit)
      • Geranylgeranylated proteins (C20 isoprene unit)
    • Fatty acylated proteins
      • Myristoylated proteins (C14)
      • Palmitoylated proteins (C16)
    • glycosylphosphatidylinositol-linked proteins (GPI-linked proteins)
      • occur in all eukaryotes, but are particularly abundant in parasitic protozoa
      • located only on the exterior surface of the plasma membrane
lipoproteins
Lipoproteins
  • particles found in plasma that transport lipids including cholesterol
  • lipoprotein classes
    • chylomicrons: take lipids from small intestine through lymph cells
    • very low density lipoproteins (VLDL)
    • intermediate density lipoproteins (IDL)
    • low density lipoproteins (LDL)
    • high density lipoproteins (HDL)