Lipids

Lipids

1. Fatty Acids

   • Carboxylic Acids with hydrocarbon chains containing between 4-36 carbons.
     • Natural fatty acids have an even Number of Carbons and are unbranched.
   • Saturated: no double bonds between carbons in the chain
     • Pack in an orderly way - extensive favorable interactions especially van der waals
   • Unsaturated
     • Two types:
       • Polyunsaturated: more than one double bond in the alkyl chain
       • Monounsaturated: one double bond between the carbons in the alkyl chain
     • Trans Fatty Acid
       • Formed due to partial hydrogenation of vegetable oils which raise LDL and increase inflammination respose
       • Trans double bond allows a given fatty acid to adopted extended conformation
         • This means they are packed more regularly and therefore have a higher melting point than cis forms
     • Cis Fatty Acid
       • Help prevent tight packing in biological molecules
         • This keeps the membranes more fluid - the degree of unsaturation in the fatty acid chain has affect on membrane fluidity. The more double bonds the more fluid.
         • It takes less thermal energy to disrupt disordering packing of unsaturated fatty acids therefore unsaturated cis fatty acids have a lower melting point.

2. Triglycerides

   • Non-polar
   • Solid ones are fats and liquid ones are oils
   • Majority of lipids found in this form
     • Primary storage form of lipids (body fat)
   • Less soluable in water than fatty acids due to the lack of charged carboxyolate groups
     • Less dense than water: fats and oils float
   • Glycerol is esterified to 3 fatty acids

3. Waxes

   • Esters of long chained saturated and unsaturated fatty acids with long chain alcohols
   • Insoluble and have high melting points
   • Variety of functions
     • storage of metabolic fuel in plankton
     • Protection and pliability of hair and skin in vertebrates
     • waterprofing of feathers in birds
     • Protection from evaporation in tropical plants and ivy
     • Used by people in lotions, ointments and polishes

4. Polar Lipids

   • Contain polar head and non-polar tail
     • Major component of biological membrane
   • Diversication
     • Modifying a different backbone
     • Changing the fatty acid
     • Modifying the head groups
   • Amphipathetic
     • Contains both hydrophobic and hydrophilic groups
     • Polar heads and 2 polar tails
     • Polar lipids replace one of the fatty acids with polar group which means that the new polar group allows more solubility in water
   • Also form micells, bilayers and liposomes

5. Membrane Lipids

   • Glycerophospholipids
     • unsaturated fatty acids often found connected to carbon 2
     • The highly polar phosphate group may be further esterifed by an alcohol such groups are called head groups.
   • Phosphatidylcholine
     • major component of most eukaryotic cell membranes
     • Many prokaryotes can synthesise this lipid
   • Sphingolipids
     • Backbone is not glycerol it is a long chain amino alcohol sphingosine
       • Joined via amide linkage opposed to ester
       • Polar head is connected to sphingosine via glycosidic or phosphodiester linkage
     • Found in the outer surface of plasma membranes
     • Sphingomyelin
       • Ceramide (sphingosine +amide-linked fatty acid) + phosphocholine attached to the alcohol
       • Abundant in myelin sheath that surrounds some nerve cells in animals