Phosphoglycerides (Membrane Lipids)
The most polar lipids are found in membranes surrounding both individual cells and the
organelles within the cell.
The most abundant lipids in membranes are phospholipids
(lipids that are phosphate esters), and primarily phosphoglycerides
Phosphoglycerides include two major types, plasmalogens
latter, the molecule is identical to a triglyceride up to the phosphoric acid unit, which is
esterified with another alcohol molecule other than glycerol.
Two common phosphatidates
(with ethanolamine group) and lecithins
(with choline group), where the
other alcohol is ethanolamine or choline (amino alcohols).
Both are important parts of
brain and nerve tissue.
Cephalins are involved with blood clotting, while lecithin, a
component of cell membranes, is the major phospholipid in pulmonary surfactant which
facilitates our respiration process.
These molecules, like soaps, are amphipathic, and this nature is central to the structure and
function of cell membranes.
An emulsifying agent aids in the suspension of triglycerides in water, and lecithins (from
soybeans, egg yolks) are used as such in foods (ice cream, mayonnaise).
Many foods are
emulsions (milk – butterfat emulsified in H
Nonglyceride Lipids (Sphingolipids)
are lipids not derived from glycerol
They are amphipathic, are structural
components of cell membranes, and derived from the amino alcohol sphingosine.
include sphingomyelins and glycosphingolipids.
The “simpler” ones are sphingomyelins
which each contain units from a fatty acid, phosphate, sphingosine, and choline.
25% of the myelin sheath which surrounds the axon are sphingomyelins (humans), as these
are essential to nerve transmission and proper cerebral function.
) include cerebrosides, sulfatides, and gangliosides.