Lipids

Lipids

1. Definition: naturally occurring organic compounds related by solubility in nonpolar organic solvents and general insolubility in water

   • Functions
     • component of membranes
     • storage form carbon and energy
     • precursor other impt substances
     • insulation barrier
     • lipoproteins that transport lipids in blood
     • natural appetite stimulant

2. Classification

   • Simple lipids
     • Trigelycerides, neutral fats
       • triesters of fatty acids with glycerol
       • found in plants and animals, major food groups of our diet
       • solid at room temp (fats; found in animals), liquid (oils; plants)
       • Animal and Plant Triglycerides
         • Animal
           • higher proportion of saturated fatty acids
           • increase melting point
           • solid or semisolid at room temp
           • palmitic and stearic acid; most abundant saturated fatty acid
         • Plant triglycerides
           • low melting point
           • liquid at room temp due to unsaturated fatty acids
           • oleic and palmitoleic acids most abundant unsaturated fatty acids
       • Functions
         • constitute fat depots, storage forms of carbon and energy
         • means by which ingested fatty acids are transported via lymphatic system and blood, in the form of lipoprotein (chylomicrons)
         • provide physical protection and thermal insulation
       • Reactions
         • Hydrolysis
           • Saponification
           • Enzymatic hydrolysis
           • Transesterification
         • Hydrogenation
         • Slow hydroylsis of fats
     • Waxes
       • neutral fats; esters of long fatty acids and high molecular alcohol
       • mixtures of chain length
       • found in several places in nature, surfaces of fruits, leaves, animal furs and feathers
   • Compound Lipids
     • Phospholipids
       • Phosphoglycerides/phosphoacylglycerols/gycerol phosphatides
       • Phosphatidic acid
       • Phosphatidylcholines
       • Phophatidylethanolamines
       • Phosphatidylinositol
       • Plasmalogens
       • Cardiolipin
     • Sphingolipids
       • Sphingomyelins
       • Cerebrosides
       • Gangliosides
     • Glycolipids
   • Derived Lipids
     • Terpenoids
       • widespread in nature; found in plants as constituents of essential oils
       • made up of isoprene units
       • 5n carbon atoms
     • Sterols
     • Fatty Acids
       • carboxylic acids w/linear hydrocarbon chains
       • unsaturation is common; confined to c18 to 20
       • Double bond system of Polyunsaturated fatty acids
         • conjugated
         • nonconjugated
       • many c-c and c-h nonpolar bonds confer nonpolar character to entire molecule despite cooh polar group; ampiphatic due to nonpolar and polar groups
       • naturally ocurring saturated fatty acids with 1-8 atoms are liquid, more c atoms=solid
       • small amounts of free fatty acids present in nature as ester or amide; at physiologic pH, ionized
       • boiling point and melting pt increase, solubility decrease with increasing chain length, decrease with increasing unsaturation
       • higher melting pts of saturated fatty acids reflect uniform rod like shape of molecules
       • nomenclature
         • delta system
         • n system
       • reactions of fatty acids
         • due to COOH group
           • esterification
           • neutralization
         • due to double bond
           • catalytic hydrogenation
           • halogenation
           • nonezymatic peroxidation
           • iodine no
     • Steroids
       • Cholesterol
       • Bile acids
       • Adrenocorticol hormones
       • Sex hormones
       • Female hormones
       • Prostaglandins
       • Leukotrienes
       • Pheromones