محاضرة الدهون 2

lipids are non-polar (hydropinghobic) compounds, soluble in organic solvents.
most membrane lipids are amphipathic, having a non-polar end and a polar end.
fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end.
a 16-c fatty acid: ch3(ch2)14-coo-
non-polar polar
a 16-c fatty acid with one cis double bond between c atoms 9-10 may be represented as 16:1 cis ?9.
double bonds in fatty acids usually have the cis configuration.
most naturally occurring fatty acids have an even number of carbon atoms.
some fatty acids and their common names:
14:0 myristic acid 16:0 palmitic acid 18:0 stearic acid 18:1 cis?9 oleic acid
18:2 cis?9,12 linoleic acid
18:3 cis?9,12,15 ?-linonenic acid
20:4 cis?5,8,11,14 arachidonic acid
20:5 cis?5,8,11,14,17 eicosapentaenoic acid (an omega-3
there is free rotation about c-c bonds in the fatty acid hydrocarbon, except where there is a double bond.
each cis double bond causes a kink in the chain.
rotation about other c-c bonds would permit a more linear structure than shown, but there would be a kink.
glycerophospholipids (phosphoglycerides), are common constituents of cellular membranes.
they have a glycerol backbone.
hydroxyls at c1 & c2 are esterified to fatty acids.
an ester forms when a hydroxyl reacts with a carboxylic acid, with loss of h2o
sphingomyelin has a phosphocholine or phosphethanolamine head group.
sphingomyelins are common constituent of plasma membranes
sphingomyelin, with a phosphocholine head group, is similar in size and shape to the glycerophospholipid phosphatidyl choline.
a cerebroside is a sphingolipid (ceramide) with a monosaccharide such as glucose or galactose as polar head group.
a ganglioside is a ceramide with a polar
head group that is a complex oligosaccharide, including the acidic sugar derivative sialic acid.
cerebrosides and gangliosides, collectively called glycosphingolipids, are commonly found in the outer leaflet of the plasma membrane bilayer, with their sugar chains extending out from the cell surface.
amphipathic lipids in association with water form complexes in which polar regions are in contact with water and hydropinghobic regions away from water.
depending on the lipid, possible molecular arrangements:
? various micelle structures. e.g., a spherical micelle is a stable configuration for amphipathic lipids with a conical shape, such as fatty acids.
? a bilayer. this is the most stable configuration for amphipathic lipids with a cylindrical shape, such as phospholipids.