Lipids

• Lipids


  Compounds that are insoluble in water but soluble in nonpolar organic solvents
• Groups of lipids


  • Open-chain compounds with a polar head group and a long nonpolar tail (fatty acids, triacylglycerols, phosphoacylglycerols, sphingolipids, glycolipids)
  • Fused-ring compounds (steroids)
• Glycerol, fatty acids, and phosphoric acid are frequently obtained as degradation products of lipids
• Fatty acids


  Carboxylic acids that may or may not have double bonds in their hydrocarbon portion
• Triacylglycerols


  Storage forms of fatty acids in which the acid part is esterified to glycerol
• Phosphoacylglycerols


  Differ from triacylglycerols in having a phosphorus-containing portion esterified to glycerol, important components of biological membranes
• Waxes


  Esters of long-chain fatty acids and long-chain alcohols
• Sphingolipids


  Do not contain glycerol, have a long-chain alcohol called sphingosine as part of their structure
• Glycolipids


  Have a carbohydrate portion covalently bonded to the lipid
• Steroids


  Have a characteristic fused-ring structure, unlike other open-chain lipids
• Lipid bilayer


  The lipid part of a biological membrane, with polar head groups in contact with aqueous interior/exterior and nonpolar portions in the interior
• Membrane fluidity


  • Presence of unsaturated fatty acids leads to greater fluidity, presence of saturated fatty acids and cholesterol tends to stiffen the bilayer, packing of molecules can undergo reversible transition from order to disorder, lateral motion of lipid molecules within one layer occurs frequently
• Membrane proteins


  Peripheral proteins are loosely attached to one surface, integral proteins are embedded solidly in the membrane
• Fluid-mosaic model


  Describes the interaction of lipids and proteins in biological membranes, proteins "float" in the lipid bilayer
• Functions of membranes


  • Transport across the membrane
  • Catalysis carried out by enzymes bound to the membrane
• Passive transport


  Substance moves from higher to lower concentration, requires no energy expenditure
• Active transport


  Moves substances against a concentration gradient, requires energy and a carrier protein
• Membrane receptors


  Bind biologically important substances that trigger a biochemical response, can be ligand-gated channel proteins
• Lipid-soluble vitamins


  • Vitamin A
  • Vitamin D
  • Vitamin E
  • Vitamin K
• Prostaglandins and leukotrienes


  Compounds derived from the unsaturated fatty acid arachidonic acid, have a wide range of physiological activities including stimulation of smooth-muscle contraction, induction of inflammation, control of blood pressure, and inhibition of blood-platelet aggregation
• Monomer


  Unit of protein - amino acids
• Monomer


  Unit of carbohydrate - monosaccharides
• Amphipathic substance


  Part of the molecules that consider a polar and non-polar
• Lipids they cannot perform a covalent bond
• Hydrolyzable lipids


  • Waxes
  • Triacylglycerols
  • Phospholipids
• Energy-storage lipids


  Lipids stored for use when energy demand is high
• Energy-storage lipids


  Triacylglycerols (Fats, Oils)
• Membrane lipids


  Lipids that are structural components of cell membranes
• Membrane lipids


  • Phospholipids (Glycerophospholipids [Lecithins, Cephalins], Sphingophospholipids [Sphingoglycolipids])
  • Cholesterol
  • Sphingoglycolipids (Cerebrosides, Gangliosides)
• Emulsification lipids


  Lipids that stabilize and disperse water-insoluble materials in aqueous solution
• Emulsification lipids


  Bile acids (Cholic acid, Deoxycholic acids)
• Messenger lipids


  Regulatory lipids that act in the tissues when they are synthesized or at other locations after transport via the bloodstream
• Messenger lipids


  • Steroid hormones
  • Eicosanoids
• Steroid hormones


  • Sex hormones
  • Adrenocorticoids
• Sex hormones


  • Estrogen
  • Androgens
  • Progestins
• Adrenocorticoids


  • Mineralocorticoids
  • Glucocorticoids
• Eicosanoids


  • Prostaglandins
  • Thromboxanes
  • Leukotirmes
• Nonhydrolyzable lipids


  • Fat-soluble vitamins
  • Eicosanoids
  • Terpenes
  • Steroids
• Protective-coating lipids


  Water-insoluble, water-repellent lipids with protective-coating and lubricant functions
• Protective-coating lipids


  Biological waxes