Lipids

• Lipids


  Class of biological molecules defined by low solubility in water and high solubility in nonpolar solvents. Either hydrophobic (containing only nonpolar groups) or amphipathic (possessing both polar and nonpolar groups). Contain C, H, O and a few polar atoms/functional groups. Include triglycerides, sterols, phospholipids.
• Classification of Lipids


  • Fatty acid-containing lipids (simple lipids: esters of fatty acids with various alcohols, complex lipids: esters of fatty acids containing groups in addition to an alcohol and a fatty acid)
  • Non-Fatty acid containing lipids (steroid, hormone, lipid-soluble vitamins)
• Fatty Acids


  A chain of carbon (even number) and hydrogen atoms with a carboxyl group at the alpha end and a methyl group at the omega end. Vary in length, saturation, shape, and natural occurrence in the body.
• Classification of Fatty Acids based on Length

  • Short-chain
  • Medium-chain
  • Long-chain
• Classification of Fatty Acids based on Saturation

  • Saturated fatty acids (all carbons bound to hydrogen, all C-C bonds are single, solid at room temperature, higher melting point)
  • Unsaturated fatty acids (some carbons form double bonds, monounsaturated: one double bond, polyunsaturated: two or more double bonds, liquid at room temperature, lower melting point)
• Saturated Fatty Acid


  • Palmitic acid
• Unsaturated Fatty Acids


  • Vary in shape (drawn either cis or trans)
• Dietary Lipids


  • Fatty Acid Composition
• Bromine Test for Unsaturation


  1. Detects the presence of unsaturation in a fatty acid or triacylglycerol

  2. A test for double bonds

  3. Bromine (Br2) reacts with compounds that have C=C bonds, causing the orange-brown color to disappear
• Triglycerides


  Also called Triacylglycerol. Most common lipid in both foods and the body. Make up about 95% of lipids found in foods. Functions: Add texture, make meats tender, preserve freshness, store as adipose tissue for energy. High levels in the blood are a risk factor for heart disease.
• Triglycerides


  Esters formed from three fatty acids connected to a glycerol backbone
• Types of Triglycerides


  • Simple triglyceride: a triester formed from the reaction of glycerol with three identical fatty acids
  • Mixed triglyceride: a triester formed from the reaction with more than one kind of fatty acid molecule
• Fats


  Saturated fatty acids dominate, closely packed together, linear, solid at room temperature, higher melting points, aka "animal fat"
• Oils


  Have mono/polyunsaturated fatty acids, have bends in fatty acid chains, liquid at room temperature, lower melting points, sources are plants
• Saponification


  Hydrolysis reaction carried out in alkaline solution forming glycerol and fatty acid salts