PHOSPHOLIPIDS Phospholipids represent unique structures in lipid organic chemistry; they are structurally related to the triglycerides in that they have a polar head and a long polar tail. The main difference is that there is a phosphoric acid group at the polar end of the molecule. The hydroxyl groups on the phosphoric acid subunit can be made into a phosphodiester bond. These will have a phosphatidic acid linkage that will be a precursor molecule in the synthesis of triglycerides. Figure 120 shows a molecule of phosphatidyl choline, which is called “lecithin”:
Figure 120.
The phospholipid bilayer is what is seen in biological systems, such as cell membranes. This will be similar to micelles except that there will be phosphate groups on one side as well as on the opposite side of the membrane with a lipid component sandwiched in between. Figure 121 shows what a lipid bilayer looks like:
223
