lipids

• Lipids


  Naturally-occurring organic substances that can be isolated from cells and tissues by extraction with a nonpolar solvent

  
• Lipids


  • A chemically diverse group of compounds, the common and defining feature of which is their insolubility in water
  • The definition of lipids is different from that used for carbohydrates and proteins because lipids are defined by a physical property (solubility) and function rather than by structure

  
• For a substance to be classified as a LIPID, the following must be met

  • The substance must be insoluble in water
  • The substance must be soluble in nonpolar solvents such as ether, chloroform, hexane
  • The substance must be found in biological systems

  
• 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

  
• Classification of lipids


  • Biochemical function
  • Based on Structure

  
• Functions of Lipids


  • STORAGE - store energy within fat cells
  • MEMBRANE COMPONENTS - parts of membranes that separate compartments of aqueous solutions from each other
  • MESSENGER - serve as chemical messengers

  
• Other functions of lipids

  • plays an important role in the structure of biologic membrane
  • important source of energy necessary for normal growth
  • enhance absorption of fat soluble vitamins
  • textural properties of other biomolecules
  • protector of vital organs
  • act as heat insulator
  • keep body warm in cold weather
  • fuel in the body producing more energy
• Classification of lipids by structure

  • Simple lipids
  • Complex lipids
  • Steroids
  • Eicosanoids

  
• Triglycerides


  Tri-esters consisting of a glycerol bound to three fatty acid molecules

  
• Fatty Acids


  Naturally occurring monocarboxylic acids with linear (unbranched) carbon chain

  
• Types of fatty acids based on carbon chain length

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

  
• Types of fatty acids based on saturation

  • Saturated - All C–C bonds are single bonds
  • Unsaturated - Monounsaturated
  • Unsaturated - Polyunsaturated

  
• Saturated fatty acids


  Fatty acids with a carbon chain in which all C–C bonds are single bonds

  
• Monounsaturated fatty acids


  Fatty acid with a carbon chain in which one carbon–carbon double bond is present

  
• Polyunsaturated Fatty Acids (PUFAs)


  Fatty acids with a carbon chain in which two or more carbon–carbon double bonds are present

  
• Shorthand notations for representing fatty acids

  • Delta system (Δ) – counting starts from the carboxyl end
  • Omega system (ω) – reference is the methyl carbon, which is the opposite of the delta carbon; also known as the nutritional notation

  
• Omega fatty acid families

  • ω-3 family – Linolenic acid
  • ω-6 family – Linoleic and Arachidonic acid
  • ω-9 family – Oleic 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

  
• Physical properties of fatty acids

  • Water Solubility
  • Melting Point

  
• 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

  
• Factors affecting melting point of fatty acids

  • Length of carbon chain
  • Degree of unsaturation (number of double bonds in a molecule)

  
• 1. chain length increases, melting point increases
• Saturated fatty acids have higher melting points than unsaturated fatty acids with the same number of carbon atoms

  
• Long-chain saturated fatty acids tend to be solid at room temperature

  
• Long-chain unsaturated fatty acids tend to be liquids at room temperature

  
• Number of "bends" in a fatty acid chain increases as the number of double bonds increases, less packing occurs, and melting point is lower

  
• Fats


  Predominantly Saturated, Solids or semisolids at room temperature, Source: Animals
• Oils


  Predominantly unsaturated, Liquids at room temperature, Sources: Plants and fish oil
• 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
• Current 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"
• Essential Fatty Acids


  Must be part of diet, Nutritionally important Omega-3 and Omega-6 fatty acids

  
• Essential fatty acids


  • Linoleic acid
  • Linolenic acid
  • Arachidonic acid

  
• Linoleic acid and linolenic acid must be obtained by mammals in their diet (specifically from plant sources)