10.4 Working with Lipids Flashcards
separation of lipids
lipids are insoluble in water
in general, complex mixtures of lipids are separated by differences in polarity or solubility in nonpolar solvents
lipid extraction requires
organic solvents
neutral lipids are extracted with
ethyl ether, chloroform, or benzene
-does not permit lipid clustering driven by the hydrophobic effect
membrane lipids are extracted by
ethanol or methanol
-reduces the hydrophobic interacts among lipid molecules
-weakens the hydrogen bonds and electrostatic interactions that bind membrane lipids to membrane proteins
commonly used extractant: chloroform, methanol, water mixture
mixture separates into 2 phases: methanol/water (top phase), chloroform (bottom phase)
-lipid remains in the chloroform layer
-more polar molecules (proteins and sugars) partition into the methanol/ water layer
adsorption chromatography separates lipids of different polarity
lipids in mixtures can be separated based on their polarity and interactions with polar material such as silica, using adsorption chromatography methods such as HPLC or TLC
HPLC: polar lipids are eluted in order of increasing polarity
TLC: less polar lipids move farthest, since less tendency to bind to silicic acid
gas chromatography resolves mixtures of volatile lipid derivatives
GC volatilizes lipids so that they can be carried by a stream of inert gas and resolved based on their ability to partition into a soluble column material
specific hydrolysis aids in determination of lipid structure
-all ester-linked fatty acids are released by mild acid or alkaline treatment
-harsher hydrolysis conditions release amide-bound fatty acids from sphingolipids
-phospholipases specific for one of the bonds in a phospholipid generate simpler compounds
mass spectrometry reveals complete lipid structure
-allows the analysis of crude mixtures of lipids without prefractionation
-can determine the length of a hydrocarbon chain or positions of double bonds!!!!!!
