Fatty Acids and Lipids Biochem 4511 Figures Essential Biochemistry 3rd Ed Pratt and Cornely Principles of Biochemistry 5th Ed Moran et al Lehninger Principles of Biochemistry 5th Ed Nelson Cox Biochemistry 3rd Ed Voet Voet Fundamentals of Biochemistry 2nd Ed Voet Voet Pratt Biochemistry 5th Ed Berg Tymoczko Stryer Fatty Acids Saturated Stearate Unsaturated Oleate Hydrophobic Tails Fatty acids Fatty acids Carboxylic acids with long hydrocarbon tails typically contain even numbers of carbons commonly C16 and C18 Saturated No double bonds Unsaturated Contain double bonds Double bonds are almost always cis and not conjugated extra methylene group separating double bonds Fatty Acids Know C12 C18 saturated fatty acids palmitoleic acid linoleic acid oleic acid and systematic names for others Unsaturated Fatty Acids Alternative naming and numbering schemes omega is the terminal carbon of the tail Unsaturated 3 fatty acid One double bond Polyunsaturated 3 fatty acids like linolenic acid multiple double bonds of which one begins at 3 Omega 6 fatty acid one in which the first double bond is 6 carbons away from terminus like linoleic acid Unsaturated Fatty Acids Nomenclature CH3CH2 CH CHCH2 5 CH2 2COOH Omega numbering Count in from the methyl end to the first double bond How would you characterize oleic acid CH3 CH2 7CH CH CH2 7COOH Nomenclature Polyunsaturated 3 fatty acids like linolenic acid have multiple double bonds starting at 3 Omega 6 fatty acid one in which the first double bond is 6 carbons away from terminus linoleic acid Alternate naming for linolenic acid is all cis 9 12 15 octadecatrienoic acid 18 carbons 3 double bonds at 9 12 and 15 Waxes Esterified Fatty Acids Waxes are long chain fatty acids C14 C36 esterified with a long chain alcohol High melting points and extremely hydrophobic water repellent Triacylglycerols Fat Storage in Cells Triacylglycerides are formed from the condensation of Stored as Fats and oils in animals and plants a mixture glycerol with 3 fatty acids of triglycerides Neutral at physiological pH Triacylglycerols Fat Storage in Cells Left Guinea pig adipocytes fat storage cells Right Arabidopsis seed cell dark spots are protein lighter surroundings are oil bodies Energy Storage and Triacylglycerols Polar bears eat for several weeks in a winter time and then go without food for up to 8 months yet remain active while fasting Polar bears consume predominantly seal fat that is VERY high in triacylglycerols The body mass of polar bears can more than triple over this short period and their bodies may consist of more than 50 percent adipose tissue During the summer polar bears don t eat or even drink as they satisfy all they dietary needs by metabolizing 2 3 pounds of fat daily Lipids Classifications Lipids for Membrane are amphipathic Hydrophobic tail Polar head group Biological membranes are composed primarily of lipids and proteins forming non covalent assemblies that define the boundaries of cells and organelles Membrane Lipids Membrane lipids combine fatty acids and polar head groups through covalent bonds Three main classes of membrane lipids o Phospholipids comprised of four components 1 Fatty acid tail groups 2 Platform to which fatty acids are attached 3 Phosphate group 4 Alcohol condensed to phosphate o Glycolipids o Cholesterol Phospholipids Four components 1 Fatty acid tail groups 2 Platform to which fatty acids are attached 3 Phosphate group 4 Alcohol attached to phosphate Alcohol head group defines the class of phospholipid Phospholipids are abundant in biological membranes Phospholipases cleave phospholipids at specific sites Know which phospholipase cleaves which ester bond 2014 John Wiley Sons Inc All rights reserved Common Phospholipids Know Phosphatidyl serine choline and ethanolamine Space Filling Model 1 stearoyl 2 oleoyl 3 phosphatidylcholine cis double bond leads to kink Fats often saturated Oils often unsaturated Glycolipids Glycolipids are membrane lipids with a sugar head group Note the glycosidic bond no reducing end Sphingolipids Instead of using glycerol as a backbone sphingolipids use sphingosine as a backbone Sphingosine is often covalently bound to another fatty acid through amide bonds Sphingolipids N acyl fatty acid sphingolipids Head group could also be a phosphoethanolamine group O3P CH2CH2NH3 In sphingomyelin the hydroxyl group is esterified to phosphorylcholine Myelin sheath around nerve cells contains a lot of sphingomyelin Sphingolipids Glycosphingolipids Glycolipid Glycans Define Blood Groups Gangliosides Complex Sphingoglycolipids Don t memorize this structure but know that gangliosides are commonly found in brain membranes and the carbohydrates protrude from membrane surface Cholesterol Know cholesterol structure Cholesterol is Hydrophobic Cholesterol is a major component of some animal membranes Cholesterol is present in plants but in very low amounts below FDA required reporting levels The rigid ring structure of cholesterol alters membrane properties and is a key component of lipid rafts which we will be discussing later Vitamin D3 is Synthesized from 7 Dehydrocholesterol Vitamin D is produced in the skin by UV light irradiating 7 dehydrocholesterol In the liver a hydroxyl group is added and a second hydroxylation in the kidney produces the active hormone Vitamin D regulates the metabolism of Ca2 in kidney intestine and bone Lipids Monolayers A single layer of oils at an air water interface The film of a soap bubble is a bilayer What do you think it looks like Lipids Micelles Single tailed lipids such as fatty acids have a wedgelike van der Waals envelope These lipids tend to form micelles of a particular favored size for each different detergent based on length and rigidity of tail Lipids Micelles Large micelles containing too many fatty acid molecules would lead to a hollow core which would fill with solvent water thermodynamically unfavorable As the micelle began to flatten into the origins of a bilayer the tails do not completely fill in the space and water gaps remain Bilayer forming ability of some lipids Membrane Lipids Membrane Bilayers Membrane lipid bilayers can extend indefinitely in any direction to form Membrane Sheets Each lipid layer is termed a leaflet Membrane Lipids Membrane Bilayers Idealized view of a typical lipid bilayer 60 fully across 15 for each head group 2x 15 for each fully extended tail group 2x Lipid Mobility Lipid tails are constantly in motion Viscosity is estimated to be that of light