Essential Cell Biology 5th edition

368 CHAPTER 11 Membrane Structure
polar
(hydrophilic)
head
CHOLINE
PHOSPHATE
GLYCEROL
O
O
CH CH 2
CH 2 N + (CH 3 ) 3
CH 2
O
P O _
head
CH 2
CH 2
O
O
nonpolar
(hydrophobic)
tails
1 2
HYDROCARBON TAIL
HYDROCARBON TAIL
C O
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 3
C
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH
CH
O
double
bond
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 3
(D)
tails
(A)
(B)
(C)
Figure 11–6 Phosphatidylcholine is the most common phospholipid in cell membranes. It is represented
schematically in (A), as a chemical formula in (B), as a space-filling model in (C), and as a symbol in (D). This particular
phospholipid is built from five parts: the hydrophilic head, which consists of choline linked to a phosphate group;
two hydrocarbon chains, which form the hydrophobic tails; and a molecule of glycerol, which links the head to the
tails. Each of the hydrophobic tails is a fatty acid—a hydrocarbon chain with a carboxyl (–COOH) group at one end;
glycerol attaches via this carboxyl group, as shown in (B). A kink in one of the hydrocarbon chains occurs where there
is a double bond between two carbon atoms. (The “phosphatidyl” part of the name of a phospholipid refers to the
phosphate–glycerol–fatty acid portion of the molecule.)
ECB5 e11.06/11.06
+
NH 3
serine
H C COO
CH 2
hydrophilic heads
O
O
P
O
Gal
CH 2
O
CH
O
C O C O
O
CH 2
OH
CH 3
OH
CH
CH
CH
O
CH CH 2
NH
C O
Figure 11–7 Different types of membrane
lipids are all amphipathic. Each of the three
types shown here has a hydrophilic head and
one or two hydrophobic tails. The hydrophilic
head is serine phosphate (shaded blue
and yellow) in phosphatidylserine, an –OH
group (blue) in cholesterol, and the sugar
galactose plus an –OH group (both blue) in
galactocerebroside. See also Panel 2–4,
pp. 72–73.
HYDROCARBON TAIL
HYDROCARBON TAIL
phosphatidylserine
(a phospholipid)
hydrocarbon tail
cholesterol
(a sterol)
CH 3 CH 3
CH
CH 2
CH 2
CH 2
CH
CH 3 CH 3
HYDROCARBON TAIL
HYDROCARBON TAIL
galactocerebroside
(a glycolipid)