Lipids

• Lipid: An organic compound found in living organisms that is insoluble (or only sparingly soluble) in water but soluble in non-polar organic solvents
• Unlike other biomolecules, lipids do not have a common structural feature that serves as the basis for defining such compounds
• Five categories of lipids:

  • 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)
• Saponification reaction - Hydrolysis reaction that occurs in a basic solution
• Classification Based on Saponification

  • Saponifiable lipids (triacylglycerols, phospholipids, sphingoglycolipids, cholesterol, and biological waxes)
  • Nonsaponifiable lipids (bile acids, steroid hormones, and eicosanoids)
• Fatty acids: Naturally occurring monocarboxylic acids with linear (unbranched) carbon chain
• Fatty acids Have even number of carbon atoms
• Two types of fatty acids: Saturated and Unsaturated (Monounsaturated and Polyunsaturated)
• Saturated fatty acids are Fatty acids with a carbon chain in which all C–C bonds are single bonds
• saturated fatty acids Numbering starts from the end of –COOH group
• Monounsaturated fatty acid: Fatty acid with a carbon chain in which one carbon–carbon double bond is present
• Unsaturated Fatty Acids have different ways of depicting the structure
• Polyunsaturated Fatty Acids are Fatty acids with a carbon chain in which two or more carbon–carbon double bonds are present
• Up to six double bonds are found in biochemically important PUFAs
• Unsaturated Fatty Acids

  • Omega (ω)-3 fatty acid

  • Omega (ω)-6 fatty acid
• Omega (ω)-3 fatty acid: Unsaturated fatty acid with its endmost double bond three carbon atoms away from its methyl end
• Omega (ω)-6 fatty acid: Unsaturated fatty acid with its endmost double bond six carbon atoms away from its methyl end
• Short-chain fatty acids have some solubility, whereas long-chain fatty acids are insoluble
• Short-chain fatty acids are sparingly soluble because of the presence of carboxylic group
• Carbohydrate glycogen - Most widespread energy storage material present in small amounts
• Major energy-storage material is triacylglycerol
• Energy-Storage Lipids: Triacylglycerols
• Two Types of Triacylglycerols: Simple triacylglycerol and Mixed triacylglycerol
• Simple triacylglycerol: Triester formed from the esterification if glycerol with three identical fatty acid molecules
• Naturally occurring simple triacylglycerols are rare
• Mixed triacylglycerol: Triester formed from the esterification of glycerol with more than one kind of fatty acid molecule
• Fats: Predominantly Saturated
• Fats are Solids or semisolids at room temperature
• Source of fat: Animals
• Oils: Predominantly unsaturated
• Oils: Liquids at room temperature
• Source of oils: Plants and fish oil
• Pure oils and fats are colorless, odorless, and tasteless
• Nations whose citizens have high dietary intakes of fats and oils tend to have higher incidences of heart disease and certain types of cancers
• Typical American diet contains too much fat
• recommended amount for total fat intake in calories:

  • 15% - Monounsaturated fat
  • 10% - Polyunsaturated
  • <10% - Saturated fats
• Saturated fats are considered bad fats
• Monounsaturated fats are considered good fats
• Polyunsaturated fats can be both good fats and bad fats
• Omega fats are important