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Spring 2011 Chem 674 2
LIPIDS• Lipids serve as energy sources, structural components, coenzymes,
electron carriers, light absorption, protein anchors, signaling• Lipids are fatty acid derivatives• Fatty acids are carboxylic acids with a hydrocarbon chain (C4 to C36)
• Hydrocarbon portion is saturated or partially unsaturated
ω3,6-PUFAs
Sources of Lipids
• Biosynthesis from acetyl-CoA• Dietary intake• Limited ability to synthesize
unsaturated fatty acids (humans)
Acyl Chains
• Vary in length
• Vary in Saturation
-double bond restricts rotation
• Van der Waals forces
-double bond interrupts
Structural Aspects• Double bonds in unsaturated FA are in cis configuration• Length and saturation determine melting point• At RT, C12:0 to C24:0 are waxy, whereas unsaturated FA are oily
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Glycerophospholipids
• Polar or charged group is attached to the third carbon of glycerol– Basis for
nomenclature
• Most abundant lipid in biological membranes
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Sphingolipids
• One fatty acid joined to sphingosine
• Polar head group
• Sphingomyelin, Glycosphingolipids,Gangliosides
• Sphingomyelin - animal cells, especially myelin
• Some involved in signal transduction & cell surface recognition
Steroids
• SteroidsSteroids:: a group of plant and animal lipids that have this tetracyclic ring structure.
Cholesterol• Cholesterol is the major sterol in animal
tissues– It is a component in plasma membranes in all
animal cells.– It is the precursor of all steroid hormones, some
vitamins and bile acids.
Close packing of cholesterol with lipids
• Makes membrane thicker• Decreases translational diffusion
Asymmetric distribution of lipids
Figure 2.14 erythrocyte
• Outer membrane is 6-fold higher in sphingolipids
• Interdigitation decreases membrane thickness
• Cholesterol stabilizes acyl chains in most extended form
Polymorphic phases of phospholipids
S = Cross-section area of polar headgroup x lipid length/ lipid volume
•S = 1 for cylindrical, conical S > 1, wedge-shaped S < 1
•Important for fusion, endocytosis, crystallization
Lipid Rafts
• Lipid ordered phase = Lo
• Eukaryotes have 1 million rafts
• Evidence of rafts in intracellular membranes
• May be just outer leaflet
• High in cholesterol, saturated FA, proteins
• Treatment with β-cyclodextrin
• Size range from 10 nm to 200 nm
• Detergent resistant?• Used by the golgi for
protein trafficking• Some contain
caveolae• Important in signaling