LIPIDS

• Michael Cooper has cut his calorie intake to nearly half of the daily requirement
• Problems faced by Michael Cooper due to lack of fat storage

  • Looks sick: bad complexion or look
  • He feels terribly cold even at 20 o C: no insulation
  • Cannot afford to starve even for a few days; no fat store to sustain survival
• Lipid


  An organic compound found in living organisms that is insoluble (or only sparingly soluble) in water but soluble in nonpolar organic solvents

  
• Lipids


  • Heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties:
  • Insoluble/immiscible in water (hydrophobic; nonpolar)
  • Soluble in organic solvents including diethyl ether, chloroform, and acetone

  
• Classification of Lipids (based on biochemical function)

  • Energy-storage lipids (triacylglycerols)
  • Membrane lipids (phospholipids, sphingoglycolipids, and cholesterol)
  • Emulsification lipids (bile acids)
  • Messenger lipids (steroid hormones and eicosanoids)
  • Protective-coating lipids (biological waxes)

  
• Classification of Lipids (based upon whether or not saponification occurs when a lipid is placed in basic aqueous solution; hydrolysis)


  • Saponifiable lipids (triacylglycerols, phospholipids, sphingoglycolipids, and biological waxes)
  • Nonsaponifiable lipids - cannot be broken up into smaller units since they do not react with water(cholesterol, steroid hormones, bile acids, and eicosanoids)

  
• Classification of Lipids (Structure)

  • Simple Lipids: Triglycerols, Fats and Oils, Waxes
  • Complex Lipids: Phospholipids, Glycolipids, Glycerophospholipids, Sphingophospholipids, Cerebrosides, Globosides, Gangliosides, Sulfatides

  
• Fatty acids


  • Most frequently encountered lipid building block (structural unit)
  • A naturally occurring monocarboxylic acid with an acid group at one end and a methyl group at the other end
  • Made up of a long hydrophobic hydrocarbon chain (highly reduced; ranging from 4 to 36 carbons) and a carboxylic acid polar group
  • Amphipathic (containing both nonpolar and polar regions)
  • Hydrophobic (nonpolar)

  
• Classification of Fatty acids (based on the length of the hydrocarbon tails)

  • Long-chain (C12 to C26)
  • Medium-chain (C8 and C10)
  • Short-chain (C4 and C6)

  
• Classification of Fatty acids (based on degree of unsaturation or presence of double bond)

  • Saturated fatty acids (SFAs)
  • Unsaturated fatty acids: Monounsaturated fatty acids (MUFAs), Polyunsaturated fatty acids (PUFAs)

  
• Saturated fatty acid


  A fatty acid with a carbon chain in which all carbon–carbon bonds are single bonds

  
• Monounsaturated fatty acid


  A fatty acid with a carbon chain in which one carbon–carbon double bond is present. In biochemically important MUFAs, configuration about thedouble bond is nearly always cis .
• Polyunsaturated fatty acid


  A fatty acid with a carbon chain in which two or more carbon–carbon double bonds are present

  
• Nomenclature of Fatty Acids

  Specifies the chain length and number of double bonds, separated by a colon. The positions of any double bonds are specified by superscript numbers following delta.

  
• Nomenclature of unsaturated fatty acids

  Unsaturated acids end in "-enoic": octadecenoic acid, octadecadienoic acid, octadecatrienoic acid

  
• Examples of unsaturated fatty acid nomenclature

  • cis-,cis-,cis-9,12,15-Octadecatrienoic acid (Linolenic acid)
  • cis-9-Octadecenoic acid (Oleic acid)

  
• Omega-3 fatty acid


  An unsaturated fatty acid with its endmost double bond three carbon atoms away from its methyl end

  
• Omega-6 fatty acid


  An unsaturated fatty acid with its endmost double bond six carbon atoms away from its methyl end

  
• Physical properties of fatty acids

  • Determined by the length of the hydrocarbon chain and the degree of unsaturation
  • Solubility in water decreases as carbon chain length increases
  • Melting points increase with increasing molar mass (longer carbon chain) and decrease with the presence of double bonds (cis configuration)

  
• Trans fatty acids are produced during hydrogenation of fish or vegetable oils and are generally recommended to be avoided due to their correlation with increased LDL (bad cholesterol) and decreased HDL (good cholesterol)

  
• Characteristics of fatty acids:

  
• Fatty acids are long straight-chain (no branching) monocarboxylic acids

  
• Fatty acids have an even number of carbon atoms (usually 12 to 24)

  
• Types of fatty acids

  • Saturated (no double bonds)
  • Unsaturated (contain one or more carbon-carbon double bonds)

  
• The double bonds in fatty acids are almost always in the cis configuration

  
• Cis double bonds result in a bent chain which does not allow fatty acids to pack as close together and consequently lower the melting point

  
• Fatty acids are rarely found free in nature but rather occur as part of the structure of more complex lipid molecules

  
• Type designation (SFA, MUFA, or PUFA)

  Polyunsaturated fatty acid (PUFA)

  
• Essential fatty acid


  A fatty acid needed in the human body that must be obtained from dietary sources because it cannot be synthesized within the body, in adequate amounts, from other substances
• Essential fatty acids

  • Linoleic acid (18:2 9,12 or 18:2 6)
  • Linolenic acid (18:3 9,12,15 or 18:3 3)

  
• PUFAs are found in plant and fish oils
• Functions of essential fatty acids


  • Needed for proper membrane structure
  • Serve as starting materials for the production of several nutritionally important longer chain omega-6 and omega-3 acids
  • When missing from the diet, the skin reddens and becomes irritated, infections and dehydration are likely to occur, and the liver may develop abnormalities

  
• Infants are especially in need of these acids for their growth
• Human breast milk has a much higher percentage of the essential fatty acids than cow's milk
• Linoleic acid


  The starting material for the biosynthesis of arachidonic acid

  
• Arachidonic acid


  The major starting material for eicosanoids, substances that help regulate blood pressure, clotting, and several other important body functions

  
• Linolenic acid


  The starting material for the biosynthesis of EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid)

  
• EPA and DHA


  Important constituents of the communication membranes of the brain and are necessary for normal brain development, also active in the retina of the eye
• Classification of lipids based on biochemical function

  • Energy-storage lipids (triacylglycerols)
  • Membrane lipids (phospholipids, sphingoglycolipids, and cholesterol)
  • Emulsification lipids (bile acids)
  • Messenger lipids (steroid hormones and eicosanoids)
  • Protective-coating lipids (biological waxes)

  
• Triacylglycerol or triglycerideor TAG


  A lipid formed by esterification of three fatty acids to a glycerol molecule, serves as energy storage in adipose cells.

  ALSO, it is a simple lipid composed of glycerol and three fatty acid molecules