Lecture 6 - Lecture6 Lecture6:LipidsandMembranes...

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Lecture 6 Lecture 6: Lipids and Membranes 10.1 Storage Lipids o fatty acids are hydrocarbon derivatives . highly reduced; oxidation is highly  exergonic  o chains are 4-36 carbons long o most commonly occurring have even numbers in unbranched chain of 12-24  carbons o common double bonds at 9, 12, 15; usually never conjugated but separated by  methylene groupl mostly in cis conformation o Nonpolar hydrocarbon chain makes it poorly soluble o Carboxylic acid is polar and accounts for slight solubility of short-chain fatty  acids o Melting points influenced by length and degree of unsaturation  o Saturated from 12-24 carbons have waxy consistency; unsaturated same length  are oily liquids o This is due to degree in packing ability: In saturated, free rotation about each C-C  bond gives chain great flexibility; the most stable conformation is the fully  extended form where sterics are minimized; these molecules can pack tightly in  crystalline  o For unsaturated, a cis forces a kink and cannot pack together as tightly; they have  a lower melting point than saturated fatty acids Triacylglycerols - have 3 fatty acids in ester linkage with single glycerol - when glycerol has two different fatty acids at 1 and 3, it is a chiral center - nonpolar, hydrophobic, insoluble in water, lower specific gravity than water so it  floats on top - Fat cells/adipocytes contain  lipases:  enzymes catalyze the hydrolysis of stored  triacylglycerols, releasing fatty acids to use as fuel - They are better for storage than glycogen or starch because the carbons are more  reduced than those of sugars, oxidation yields more than twice as much energy - Since they are hydrophobic and unhydrated, organism does not have to carry  around associated extra water weight - Provides insulation against low temperatures, has low density - Huge fat reserved for bear hibernation, polar animals, sperm whales to match  buoyancy of surrounding water during deep dives Sperm Whales 90% of head mass is blubbery mass of oil Mixture is liquid at normal temperature but begins to crystallize at about  31 degrees and become solid when the temperature drops Undergoes change in buoyancy to match density of surroundings Water is much colder and denser
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Lecture 6 Importance of freezing point of oil: then the temperature of oil is lowered  during deep dice, it congeals or crystallizes and becomes denser Mechanisms allow rapid cooling of oil during a dive When returning to surface, the hardened oil warms and melts, decreasing 
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