lipids and membranes

lipids are water-insoluble that are either hydropinghobic (nonpolar) or amphipathic (polar and nonpolar regions).

there are many types of lipids:
1) fatty acids
• the simplest with structural formula of r-cooh where r = hydrocarbon chain.
• they differ from each other by the length of the tail, degree of unsaturation, and position of double bonds.
• pka of -cooh is 4.5-5.0 > ionized at physiological ph.
• if there is no double bond, the fatty acid is saturated.
• if there is at least one double bond, the fatty acid is unsaturated.
• monounsaturated fatty acids contain 1 double bond polyunsaturated fatty acids have >2 double bonds.
• iupac nomenclature =?n represents where double bond occurs as you count from the carboxyl end (see table 9.1).
e.g. -enoate one double bond
-dienoate 2 “
-trienoate 3 “
-tetraenoate 4 “
• can also use a colon separating 2 numbers, where the first number represents the number of carbon atoms and the second number indicates the location of the double bonds.
e.g. linoleate 18:2?9,12 or cis,cis -?9,12octadecadienoate
• physical properties differ between saturated and unsaturated fatty acids.
saturated = solid at rt often animal source e.g. lard
unsaturated = liquid at rt plant source e.g. vegetable oil
• the length of the hydrocarbon tails influences the melting point.
• as the length of tails increases, melting points increases due to number of van der waals interactions.
• also affecting the melting point is the degree of unsaturation.
• as the degree of unsaturation increases, fatty acids become more fluid > melting point decreases ( kinks in tails decrease number of van der waals interactions