Biology Reference
In-Depth Information
FATTY ACID
structure
omega class
STEARIC ACID
18:0
saturated
OH
C
O
OLEIC ACID
18:1
Δ
9
omega-9
OH
9
10
C
O
LINOLEIC ACID
18:2
Δ
9,12
omega-6
OH
12 13
9 0
C
O
α
-LINOLENIC ACID
18:3
Δ
9,12,15
omega-3
OH
12
13
15
16
9
0
C
O
γ
-LINOLENIC ACID
18:3
Δ
6,9,12
omega-6
12
13
9
10
6
7
OH
C
O
FIGURE 4.3
Structure of the 18-carbon sequence of important membrane fatty acids.
acids with their omega designations. For example,
a
-linolenic acid (18:3
6
9,12,15
) has the last
of its 3 double bonds 3 carbons from the terminal (omega) end and so is an omega-3 fatty
acid. Although docosahexaenoic acid (22:6
6
4,7,10,13,16,19
) has 4 more carbons in its chain
than
a
-linolenic acid, it too is an omega-3 fatty acid. The omega designation is therefore
independent of fatty acid chain length. It is now known that the 18-C omega-3 fatty acid
a
-linolenic acid is far more similar to the 22-C omega-3 fatty acid docosahexaenoic acid in
supporting human health than it is to the saturated 18-C stearic acid (18:0) or the monoun-
saturated 18-C oleic acid (18:1
6
9
). By this system the major classes of fatty acids are satu-
rated, omega-9, omega-6 and omega-3, although other minor classes of fatty acids also exist.
A strong case has been made for the number and location of double bonds being more
important for human health than chain length. The class known as omega-3s has been of
particular importance. Omega-3 fatty acids play crucial roles in cardiac, brain, and neuro-
logical function, as well as having roles in normal growth and development
[12,13]
.Since
man cannot make double bonds (desaturate) beyond the
9 position, essential omega-3
6
