lipids chem

• Lipids


  Compounds of biological origin that dissolve in nonpolar solvents such as chloroform and diethyl ether

  
• Lipids


  • Function as energy-storage molecules and chemical messengers
  • Include fats, waxes, oils, hormones, and certain components of membranes

  
• Functions of lipids


  • Storage molecules for energy (fats and oils)
  • Structural components of cellular membranes
  • Protective molecules (waxes)
  • Intracellular messengers
  • Pigments
  • Insulation

  
• Two main categories of lipids

  • Hydrolyzable lipids
  • Non-hydrolyzable lipids

  
• Hydrolyzable lipids


  Lipids that contain an ester functional group and may be hydrolyzed in water. Examples include waxes, triacylglycerols, and phospholipids.

  
• Non-hydrolyzable lipids


  Lipids that lack an ester functional group and are considered non-hydrolyzable. Examples include steroids, terpenes, eicosanoids, and fat-soluble vitamins (A, D, E, and K).

  
• Waxes


  • Simplest hydrolyzable lipid
  • Esters formed from a high molecular weight alcohol and a fatty acid
  • Very hydrophobic due to long carbon chains

  
• Waxes


  • Paraffin wax
  • Triacontanyl palmitate
• Triacylglycerols (TAGs)


  • Triesters of glycerol and fatty acids
  • Most long-chain carboxylic acids of biological origin are found as esters of glycerol
  • Oils from plants and fats of animal origin are triacylglycerols

  
• Types of fatty acids

  • Saturated fatty acids (compact, solid at room temperature, e.g. stearic acid)
  • Unsaturated fatty acids (less compact, liquid at room temperature, e.g. linoleic acid)
  • Trans fatty acids (created by hydrogenation, raise LDL cholesterol)

  
• Phospholipids


  • Major membrane lipids that consist of lipid bilayers
  • Act as a barrier to protect the cell and enable multiple cellular processes to occur in subcellular compartments

  
• Types of phospholipids


  • Phosphoacylglycerols (phosphoglycerides)
  • Sphingomyelins

  
• Phosphoacylglycerols


  Derived from glycerol

  
• Sphingomyelins


  • Derived from sphingosine
  • Component of the lipid bilayer of cell membranes
  • The coating that surrounds and insulates nerve cells, the myelin sheath, is rich in sphingomyelin and vital for proper nerve function
• Fat-soluble vitamins


  • Vitamin A
  • Vitamin D
  • Vitamin E
  • Vitamin K
• Vitamin A


  • Obtained from fish liver oils and dairy products, synthesized from β-carotene
  • Deficiency causes night blindness, dry eyes and skin
• Vitamin D


  • Vitamin D3 is the most abundant
  • Regulates calcium and phosphorus metabolism
  • Deficiency causes rickets
• Vitamin E


  • Group of structurally similar compounds, α-tocopherol is the most potent
  • Acts as an antioxidant, protects unsaturated side chains in fatty acids from oxidation
  • Deficiency causes neurological problems
• Vitamin K


  • Regulates the synthesis of prothrombin and other proteins needed for blood clotting
  • Deficiency leads to excessive and sometimes fatal bleeding due to inadequate blood clotting
• Eicosanoids


  • Derived from the word eikosi, meaning 20
  • Group of hormones belonging to the local hormones
  • Synthesized from arachidonic acid in response to external stimulus, not stored in cells
• Classes of eicosanoids


  • Prostaglandins
  • Thromboxanes
  • Leukotrienes
  • Prostacyclins
• Prostaglandins


  • Mediators of pain and inflammatory response
  • Produced in the hypothalamus in response to chemical messengers released during inflammation
  • Have various physiological effects such as lowering blood pressure, gastric secretions, and stimulating uterine contraction
• Thromboxanes


  Vasoconstriction, trigger blood platelet aggregation
• Leukotrienes


  Synthesized by immune cells, cause chemotaxis and airway narrowing in the lungs
• Prostacyclins


  Vasodilation, inhibit blood aggregation
• Terpenes


  • Aromatic compounds found mainly in plants, create characteristic scents
  • Made up of isoprene units
  • Terpenoids contain isoprene units and an oxygen atom
• Steroids


  • A class of lipid molecules identifiable by their structure of four fused rings
  • Although they do not resemble other lipids structurally, they are included in the lipid category because they are hydrophobic and insoluble in water
  • Many steroids also have an -OH functional group and are classified as alcohols, or sterols

  
• Cholesterol


  • The most common steroid, synthesized in the liver
  • Precursor to many steroid hormones, vitamin D, and bile acids
  • Key component of cell membranes, altering their fluidity and dynamics
  • Synthesized in the body from squalene
• Steroid hormones


  • Estradiol and estrone (estrogens)
  • Progesterone (pregnancy hormone)
  • Testosterone and androsterone (androgens)
• Adrenal cortical steroids


  • Cortisone and cortisol (anti-inflammatory, regulate carbohydrate metabolism)
  • Aldosterone (regulates blood pressure and volume by controlling Na+ and K+ concentration)
• Qualitative test for lipids

  
• Isolation of lecithin