Essential Cell Biology 5th edition

74
PANEL 2–5 FATTY ACIDS AND OTHER LIPIDS
FATTY ACIDS
All fatty acids have a carboxyl
group at one end and a long
hydrocarbon tail at the other.
COOH COOH COOH
Hundreds of different kinds of fatty acids exist. Some have one or more double bonds in their
hydrocarbon tail and are said to be unsaturated. Fatty acids with no double bonds are saturated.
– O
– O
O O
C
C
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
oleic
acid
This double bond
is rigid and creates
a kink in the chain.
The rest of the chain
is free to rotate
about the other C–C
bonds.
stearic
acid
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH
CH 2
CH 2
CH 2
CH 2
CH
CH 2
space-filling model carbon skeleton
UNSATURATED
SATURATED
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 2
CH 3
stearic
acid
(C 18)
CH 2
CH 2
CH 2
CH 3
palmitic
acid
(C 16)
CH 2
CH 2
CH 2
CH 2
CH 2
CH 3
oleic
acid
(C 18)
TRIACYLGLYCEROLS
H 2 C O
O
C
HC O
O
C
H 2 C O
O
C
Fatty acids are stored in cells as an energy reserve
(fats and oils) through an ester linkage to
glycerol to form triacylglycerols.
H 2 C
HC
H 2 C
OH
OH
OH
glycerol
CARBOXYL GROUP
PHOSPHOLIPIDS
Phospholipids are the major constituents
of cell membranes.
If free, the carboxyl group of a
fatty acid will be ionized.
C
O
O _
CH 2
CH
O
polar group
O
P O _
O
CH 2
hydrophilic
head
choline
But more often it is linked to
other groups to form either esters
O
C
O
C
hydrophobic
fatty acid tails
or amides.
O
phosphatidylcholine
C
N
H
general structure of
a phospholipid
In phospholipids, two of the –OH groups in
glycerol are linked to fatty acids, while the third
–OH group is linked to phosphoric acid. The
phosphate, which carries a negative charge, is
further linked to one of a variety of small polar
groups, such as choline.