Table 1.7 Examples of the classification ofa-phosphatidyl lipids. Common names are
given in bracketsR 2 Classification Glycerol Phosphatidyl glycerolCholine Phosphatidyl choline
(lecithins)Inositol Phosphatidyl inositolSerine Phosphatidyl serine Ethanolamine Phosphatidyl ethanolamine
(a-cephalins)Thea-phosphatidyl lipids are further subdivided according to the nature of
their R 2 residues (Table 1.7). The R 2 groups of plasmalogens and ether phos-
pholipids are similar to the R 2 groups of the phosphatidyl lipids, whilst the
sphingomyelins have a choline residue.
Phospholipid molecules form the lipid bilayer of cell membranes (Appendix 3).
Plasmalogens and sphingomyelins are particularly abundant in brain tissue.
1.5.7 Glycolipids
Most glycolipids are glycosides with a sphingosine derivative (ceramide) acting
as the aglycone. They are subdivided according to the nature of the carbohy-
drate residue (Table 1.8).
Cerebrosides occur mainly in brain and nervous tissues. Sulphatides are the
main sulpholipids in the brain, where they account for approximately 15%of the
white matter. Gangliosides are particularly abundant in the cells of the central
nervous system. They are believed to be the receptors (Figure A4.1 and Appen-
dix 5) for toxins, such as cholera and tetanus toxins, and some viruses, such as
the influenza virus.
Table 1.8 Examples of the subclassification of glycolipids. R groups are normally long saturated
hydrocarbon chains with 21–25 carbon atoms (a C22–C26 fatty acid residue)
Subclassification Structure
Cerebrosides (neutral glycolipids)
have either a glucose or galactose
carbohydrate residue.
CHCHCHNHCORO
OHOHOCH 2HH
HOHH OHCH 2CH 3 (CH 2 ) 12 CHOHAβ-D-glucose residue(continues overleaf)LIPIDS 25