Lipids

• LIPIDS


  organic compound found in living organisms that is insoluble (or only sparingly soluble) in water but soluble in non-polar organic solvents.
• Insoluble or sparingly soluble in water

  Soluble in non-polar organic solvents


  They are classified on the basis of solubility not on any functional groups
• triacylglycerols


  Five Categories of Lipids

  Energy-storage lipids
• phospholipids, sphingoglycolipids, and cholesterol


  Five Categories of Lipids

  Membrane lipids
• bile acids


  Five Categories of Lipids

  Emulsification lipids
• steroid hormones and eicosanoids)


  Five Categories of Lipids

  Chemical messenger lipids
• biological waxes


  Five Categories of Lipids

  Protective-coating lipids
• Saturated Fatty Acids


  Numbering starts from the end of -COOH group

  See structural notation: it indicates number of C atoms

  Example - Lauric acid has 12 C atoms and no double bonds so it is (12:0)
• Unsaturated Fatty Acids


  is a fatty acid with a carbon chain in which one carbon-carbon double bond is present.

  Different ways of depicting the structure
• polyunsaturated fatty acid


  is a fatty acid with a carbon chain in which two or more carbon-carbon double bonds are present.
• Omega (ω)-3 fatty acids


  - An unsaturated fatty acid with its endmost double bond three carbon atoms away from its methyl end.
• Omega(ω)-6 fatty acid


  is an unsaturated fatty acid with its endmost double bond six carbon atoms away from its methyl end.
• Omega Acids


  Essential Fatty Acids: Must be part of diet
• Linolenic acid

  Linoleic acid


  - Omega-3

  - Omega-6
• Linoleic Acid Deficiency:

  Skin redness - becomes irritated

  Infections and dehydration

  Liver abnormalities

  Children need it the most

  Human milk has more than cow's milk
• American Diet


  Sufficient in omega 6 fatty acids

  Deficient in omega 3 fatty acids

  Fish - good source for omega 3 fatty acids

  High rate of heart disease may be due to imbalance in omega 3 and 6 fatty acids

  Ideal ratio: Omega 6 : Omega 3 (4 - 10 g: 1g)
• Water solubility


  : Short chain fatty acids have some solubility whereas long chain fatty acids are insoluble

  Short chain fatty acids are sparingly soluble because of carboxylic acid polar group
• Energy-Storage Materials: TRIACYLGLYCEROLS


  With the notable exception of nerve cells, human cells store small amounts of energy providing materials:

  The most widespread energy storage material -carbohydrate glycogen

  Present in small amounts
• Two Types of Triacylglycerols

  Simple Triacylglycerols:


  Three identical fatty acids are esterified

  Naturally occurring simple triacylglycerols are rare
• Mixed Triacylglycerols


  A triester formed from the esterification of glycerol with more than one kind of fatty acid

  
  

  are found and are different even from the same source depending on the feed, e.g., corn, peanut and wheat -fed cows have different triacylglycerols
• Physical State: fats


  Predominantly Saturated

  Solids or semisolids at room temperature
• physical state: oils


  Predominantly unsaturated

  Liquids at room temperature
• source: fats


  Animal source and tasteless
• source: oils


  Plants and fish oil
• 15% - Monounsaturated fat

  10% - Polyunsaturated

  <10% - Saturated fats


  Current recommended amounts are: total fat intake in calories:
• good fats

  bad fats

  good and bad fats


  Monounsaturated fats are considered "_______"

  Trans-monounsaturated fats are considered "_______"

  Polyunsaturated fats can be both "______" and "_______"
• Partial Hydrolysis

  Breaking of 1-2 ester bonds to give rise to mono- or diacylglycerol and fatty acid(s)

  Carried out by enzymes produced by the pancreas
• esters and alkenes


  Chemical Properties due to two functional groups:
• Hydrolysis


  : Partial hydrolysis of triacylglycerols
• Saponification


  Hydrolysis in basic solution: Produce salt of fatty acid and glycerol
• Hydrogenation


  Addition of hydrogen across double (=) bond - increases degree of saturation

  
  

  Many food products are produced by partial hydrogenation of oils and fats

  Peanut oil + H2 Peanut Butter

  Vegetable oil + H2 Margerine
• Oxidation


  Double bonds in triacylglycerols are subject to oxidation with oxygen in air (an oxidizing agent )-Leads to C=C breakage
• PHOSPHOLIPIDS


  All cells are surrounded by a membrane that confines their contents.

  Up to 80% of the mass of a cell membrane can be lipid materials and these lipid materials are dominated _____
• phosphate


  contains one or more fatty acids, a

  ___ group, a platform molecule (glycerol or sphingosine) to which the fatty acid(s) and the ______ group are attached, and an alcohol that is attached to the ____ group.
• Glycerophospholipids


  is a lipid that contains two fatty acids and a phosphate group esterified to a glycerol molecule and an alcohol esterified to the phosphate group.

  
  

  undergo hydrolysis and saponification reactions in a manner similar to that for triacylglycerols
• are ester linkages


  All attachments (bonds) between groups in a glycerophospholipid
• 4 AND 3


  Glycerophospholipids have _ ester linkages as contrasted to _ester linkages in triacylglycerols.
• choline, ethanolamine, or serine


  respectively known as phosphatidylcholines, phosphatidylethanolamines, and phosphatidylserines.
• TRIACYLGLYCEROLS


  serve as energy storage molecules
• Glycerophospholipids


  function as components of cell membranes