lecithin and 23 °C for dimyristoyl lecithin. This heat absorption is the result of
changes in the form of molecules in the fatty acid chain; from a solid, trans zigzag
stage, it changes to a highly fluid liquid crystal state with a gauche conformation
(alternating rotated isomers; see Fig. 8.21).
The presence of unsaturated fatty acids lowers the phase transition temperature.
In the case of dioleyl lecithin, the temperature is around −22 °C. To preserve life
activities, the biomembrane must always be kept in a state to allow activity, and it is
entirely appropriate that the biomembrane lipids largely contain unsaturated fatty
Fig. 8.20 Sterol compounds
Table 8.2 Fatty acid composition in squid nerve cell membranes
Tissue and lipids
Brain
Fin nerves
Tissue weight (mg)
39.2
41.8
Total lipid weight (mg)
7.48
5.35
Cholesterols (%)
33
39
Cardiolipin (%)
2
0
Free fatty acids (%)
3
0
Phosphatidylethanolamine (%)
32
20
Phosphatidycholine (%)
19
29
Phosphatidylserine and phosphatidylinositol (%)
8
5
Sphingomyelin (%)
1
5
8.3 Bio Materials
251