Midterms 2

• Lipids

  A biomolecule alongside carbohydrates, proteins, and amino acids
• Lipids


  • Present in humans, animals, plants, and other microorganisms
  • Insoluble (or only sparingly soluble) in water but soluble in non-polar organic solvents
  • Do not have a common structural features that serves as the basis for defining such compounds
• Animal lipids


  • Animal fat, egg yolk, butter, and cheese
• Plant lipids


  • Oils
• Five categories of lipids

  • Energy-storage lipids
  • Membrane lipids
  • Emulsification lipids
  • Chemical messenger lipids
  • Protective-coating lipids
• Saturated fatty acids

  Carboxylic acids with linear (unbranched) carbon chain, all C-C bonds are single bonds
• Unsaturated fatty acids

  Carboxylic acids with linear (unbranched) carbon chain, contain double bonds<|>Monounsaturated - one C=C bond<|>Polyunsaturated - 2 or more C=C bonds
• Omega-3 fatty acids


  Unsaturated fatty acids with the endmost double bond three carbon atoms away from the methyl end
• Omega-6 fatty acids


  Unsaturated fatty acids with the endmost double bond six carbon atoms away from the methyl end
• Essential fatty acids


  Fatty acids that must be obtained from dietary sources, not synthesized within the body
• Triacylglycerols


  The most widespread energy storage material, concentrated primarily in fat cells (adipocytes)
• Simple triacylglycerols


  Three identical fatty acids esterified with glycerol
• Mixed triacylglycerols


  Triesters formed from the esterification of glycerol with more than one kind of fatty acid
• Fats


  Predominantly saturated, solids or semisolids at room temperature, from animal sources
• Oils


  Predominantly unsaturated, liquids at room temperature, from plant and fish sources
• Saturated fats


  Considered "bad fats" as they solidify at room temperature and can cause blockage in blood vessels
• Monounsaturated fats


  Considered "good fats" as they prevent cardiovascular diseases and cancer
• Trans-monounsaturated fats


  Considered "bad fats"
• Polyunsaturated fats


  Can be both "good fats" and "bad fats" depending on the type, omega-3 and omega-6 are important "good fats"
• Partial hydrolysis of triacylglycerols


  Breaking of 1-2 ester bonds to give rise to mono- or diacylglycerol and fatty acid(s), carried out by pancreatic lipase
• Saponification


  Hydrolysis of fats in basic solution to produce salt of fatty acid and glycerol, used for soap making
• Hydrogenation

  Addition of hydrogen across double bonds to increase degree of saturation, used to produce butter or margarine
• Oxidation of triacylglycerols

  Double bonds are subject to oxidation with oxygen, leading to C=C breakage and formation of aldehydes or carboxylic acids with objectionable odors (rancidity)
• All cells are surrounded by a membrane that confines their contents
• Degree of saturation

  Elevated temperature with catalysts like iron, copper, cobalt
• Partial hydrogenation of oils and fats


  To produce butter or lard
• 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
• Oxidation of alkenes


  May result into two short chain molecules – an aldehydes or a carboxylic acid
• Rancidity

  Aldehydes and/or carboxylic acids produced often have objectionable odors - fats and oils are said to be rancid [due to oxidation; leads to the formation of peroxides, and the later reaction will lead to unwanted odor]
• Antioxidants


  Added as preservatives to avoid unwanted oxidation process, e.g., Vitamin C and vitamin E
• Up to 80% of the mass of a cell membrane can be lipid materials and these lipid materials are dominated by phospholipids
• Phospholipid


  Contains one or more fatty acids, a phosphate group, a platform molecule (glycerol or sphingosine) to which the fatty acid(s) and the phosphate group are attached, and an alcohol that is attached to the phosphate group
• Glycerophospholipid


  A lipid that contains two fatty acids and a phosphate group esterified to a glycerol molecule and an alcohol [choline, ethanolamine, serine] (collectively known as cephalins) esterified to the phosphate group
• All attachments (bonds) between groups in a glycerophospholipid are ester linkages
• Glycerophospholipids have four ester linkages as contrasted to three ester linkages in triacylglycerols
• Phosphatidylcholines, phosphatidylethanolamines, and phosphatidylserines


  The three types of glycophospholipids based on the alcohol attached to the phosphate group
• Glycerophospholipids


  • Structurally similar to triacylglycerols, but have different biochemical functions (brain and lungs)
  • Have function in blood coagulation (soluble in methanol and ethanol)
• Triacylglycerols

  Serve as energy storage molecules