Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morgan, Martin Raff, Keith Roberts, Peter Walter by by Bruce Alberts, Alexander Johnson, Julian Lewis, David Morg

THE LIPID BILAYER
567
hydrophilic
head group
hydrophobic
tails
phosphatidylcholine are the most abundant ones in mammalian cell membranes
(Figure 10–3A–C).
Another important class of phospholipids are the sphingolipids, which are built
from sphingosine rather than glycerol (Figure10–3D–E). Sphingosine is a long acyl
chain with an amino group (NH 2 ) and two hydroxyl groups (OH) at one end. In
sphingomyelin, the most common sphingolipid, a fatty acid tail is attached to the
amino group, and a phosphocholine group is attached to the terminal hydroxyl
group. Together, the phospholipids phosphatidylcholine, phosphatidylethanolamine,
phosphatidylserine, and sphingomyelin constitute more than half the
MBoC6 m10.02/10.02
mass of lipid in most mammalian cell membranes (see Table 10–1, p. 571).
CH 2
O
(A)
O
CH
O
C O C O
+ NH 3
CH 2
CH 2
O
P
O
CH 2
CHOLINE
PHOSPHATE
GLYCEROL
1 2
FATTY ACID TAIL
O
FATTY ACID TAIL
CH 2
O
H
O
CH
O
C O C O
+ NH 3
C
CH 2
O
P
O
CH 2
(B)
COO
O
CH 2 CH CH 2
O O
C O 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 cis-double
bond
CH 2 CH
CH CH 2
2
CH
CH 2
2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH
CH 2
3
CH 3
CH 2
O
O
CH 3 CH 3
CH 3 CH 3 CH 3 CH 3
+ N
+ N
CH 2
CH 2
O
CH
O
C O C O
CH 2 N + (CH 3 ) 3
CH 2
O
P O _
O
CH 2
O
P
O
CH 2
O
OH
CH
CH
CH
(C)
O
CH
NH
C
O
CH 2
O
P
O
CH 2
O
Figure 10–2 The parts of a typical
phospholipid molecule. This example
is a phosphatidylcholine, represented (A)
schematically, (B) by a formula, (C) as a
space-filling model (Movie 10.1), and
(D) as a symbol.
Figure 10–3 Four major phospholipids in
mammalian plasma membranes. Different
head groups are represented by different
colors in the symbols. The lipid molecules
shown in (A–C) are phosphoglycerides,
which are derived from glycerol. The
molecule in (D) is sphingomyelin, which
is derived from sphingosine (E) and is
therefore a sphingolipid. Note that only
phosphatidylserine carries a net negative
charge, the importance of which we discuss
later; the other three are electrically neutral at
physiological pH, carrying one positive and
one negative charge.
OH
OH
HC CH CH 2
CH NH +
3
CH
(D)
hydrophilic
head
hydrophobic
tails
FATTY ACID TAIL
FATTY ACID TAIL
FATTY ACID TAIL
FATTY ACID TAIL
FATTY ACID TAIL
FATTY ACID TAIL
FATTY CHAIN
FATTY ACID TAIL
FATTY CHAIN
phosphatidylethanolamine phosphatidylserine phosphatidylcholine sphingomyelin sphingosine
(A) (B) (C) (D) (E)