Biology Reference
In-Depth Information
--
HO
2
S
O
CH2
HO
O
OH
CH2
O
OH
HO
O
O
CH2
O
R'
OH
C
HC
2HC
O
O
R"
C
O
OH
MGDG
DGDG
SQDG
FIGURE 5.25
Structure of three closely related galactosyl diacylglycerols commonly found in plant thylakoid
(photosynthetic) membranes.
G.
MEMBRANE LIPIDS FOUND IN LOW ABUNDAN
CE
There are countless numbers of unusual lipids found in membranes in almost undetect-
able amounts. For example, the oxidation of polyunsaturated fatty acids produces countless
byproducts whose structures and biological functions are largely unknown. A few of the
more common lipids whose structures and function are appreciated are discussed below.
Free Fatty Acids and Lysolipids
Under physiological conditions phospholipids are degraded (hydrolyzed) by a variety of
phospholipases (
Figure 5.24
)
[38]
. The phospholipases A
1
and A
2
cleave the hydrophobic
TABLE 5.4
Polar Lipid Composition of the Plant Thylakoid (Photosynthetic)
Membrane.
Lipid
Mol %
MGDG
48
DGDG
25
PG
13
SQDG
8
PC
2
Other
4
