Lipids

• Lipids are defined as water-insoluble (or only sparingly soluble) organic compounds found in biological systems

  
• Lipids have widely varied structures compared to carbohydrates, proteins, and nucleic acids
• Fatty acids are the simplest lipids, composed of a long hydrocarbon chain (tail) and a terminal carboxyl group
• Most naturally occurring fatty acids have an even number of carbon atoms (14-24) and are either saturated or unsaturated (mono- or polyunsaturated)
• Fatty acids can also be referred to by their common names, such as lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid
• In the delta nomenclature system for fatty acids, the number of carbons, double bonds, and the position of the first double bond are indicated
• Double bonds in naturally occurring fats are almost always in the cis-configuration, while trans fats are found in processed foods and linked to health problems
• The melting point of a fatty acid is influenced by the length of its hydrocarbon chain and the number of double bonds
• Fatty acids are either entirely hydrophobic or amphiphilic (amphipathic), not amphoteric
• Triacylglycerols (TAGs) are esters derived from glycerol and three fatty acids, serving as the main constituents of body fat and vegetable oils
• Triacylglycerols are essential for long-term energy storage and insulation in the body, being nonpolar, hydrophobic, and insoluble in water
• Oils are mixtures of triacylglycerols (TAGs)
• Triacylglycerols (TAGs) are tested for the degree of unsaturation using the iodine number, which measures the number of grams of iodine that adds to 100g of the sample
• The degree of unsaturation in fats and oils influences the firmness of foods at room temperature
• Vegetable oils tend to be liquid while animal fats tend to be solid due to the degree of unsaturation
• Manufacturers protect fat-containing products against rancidity by sealing products in air-tight, non-metallic containers, adding antioxidants like BHA and BHT, and through hydrogenation
• Fatty Acids (FAs) are the simplest lipids, many other types of lipids either contain FAs or are derived from FAs
• Energy is stored as fat (TAGs) because it yields more energy per gram than carbohydrates or proteins
• Waxes are esters of long chain fatty acids and long chain alcohols
• In an aqueous environment, amphiphatic lipids form micelles, bilayers, or liposomes depending on the lipid concentration and the nature of the polar head groups
• Cholesterol can form esters with organic alcohols and plays a role in biological membranes
• Sphingolipids, based on the alcohol sphingosine, have a variable polar head group and are involved in the development of myelin sheathing
• Phospholipase A2 cleaves arachidonic acid-containing membrane phospholipids in response to hormonal signals, releasing arachidonate which is metabolized by COX to yield biologically potent molecules
• Arachidonate metabolites like eicosanoids (prostaglandins, thromboxanes, and leukotrienes) have various physiological effects including muscle contraction, inflammation, and blood clot formation
• Steroid hormones derived from cholesterol affect gene expression and are synthesized from cholesterol
• Bile salts, synthesized from cholesterol in the liver, act as detergents in the small intestine
• Active vitamin D3 is synthesized from cholesterol through steps in the skin, kidney, and liver
• Triacylglycerols (TAGs)


  Oils are mixtures of triacylglycerols

  
• Iodine number


  Used as a test for the degree of unsaturation in fats and oils - no. of grams of iodine that adds to 100g of the sample
• Lipid


  Amphiphilic (amphipathic) molecule, can be hydrolysable or non-hydrolysable, and can be simple or complex

  
• Lipids


  • Different kinds of lipids have different roles
  • Fatty acids can be represented using different nomenclature
  • Lipid structures relate to their physical properties, reactions, and functions
  • Different classes of lipids can be recognised from their chemical formulae

  
• Saponification


  Action of soap
• Degree of unsaturation in fats and oils

  • Influences the firmness of foods at room temperature
  • Influences stability with respect to oxidation
• Antioxidants (BHA and BHT)


  Added to fat-containing products to compete for oxygen and protect against rancidity
• Hydrogenation


  One of the ways manufacturers protect fat-containing products against rancidity
• Fatty acids (FAs)


  The simplest lipids, many other lipids either contain FAs or are derived from FAs
• Formation of a triacylglycerol

  Ester formation

  
• Waxes


  Esters of long chain fatty acids and long chain alcohols

  
• Beeswax is solid at temperatures below 40°C
• Amphiphatic lipids


  In an aqueous environment, they will form micelles, bilayers or liposomes depending on lipid concentration and nature of polar head groups