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chapter 10
Heteropolysaccharides I: Glycoproteins and Glycolipids
(a)
Phosphoglycerldes
f i
G lycerol
moiety
I
S.
Q
Fatty ad d
resid ues
C H ,
C H ,
r o — CH ,— C H — N — C H ,
;...................
=
4
.........
Choline moiety
Phosphatidylcholine
(ledthin)
O
° %
/ °
.................. ...............
~ o '
' T o — C H ,— C H — N H *]
Ethanolam ine moiety
Phosphatidylethanolam ine
O — C H — C H — N H j ;
I
C O O "
.
Serin e moiety
Phosphatidylserine
O
F I G U R E 1 0 -5
C H ,
Structures of some membrane lipids.
synthetic detergents or bile salts to disrupt the lipid-protein
interactions.
Carbohydrate residues are covalently linked (exclu-
sively on the external side of the bilayer) to proteins or
lipids to form glycoproteins or glycolipids, respectively,
both of which are asymmetrically distributed in the lipid
bilayer (Figure 10-7). Fluidity of the membrane structure
is determined by the degree of unsaturation of the hydro-
carbon chains of the phospholipids and by the amount
of cholesterol in the membrane. Hydrocarbon chains
with cis-double bonds produce kinks and allow a greater
degree of freedom of movement for the neighboring alkyl
side chains; hence, these unsaturated chains give rise to
more fluidity than do saturated alkyl chains, which asso-
ciate in ordered arrays. Cholesterol, an inflexible poly-
cyclic molecule, is packed between fatty alkyl chains, the
ring bearing the polar hydroxyl group interacting with the
polar groups of phospho- and glycolipids. The presence
of cholesterol disrupts the orderly stacking of alkyl
side chains, restricts their mobility, and causes increased
