Phospholipids:
Phosphoglyceride and sphingolipids
Glycolipids
Sterols ( is only found in animals)
Membrane lipids are amphipathic.
There are three major classes of lipids:
Figure 10-2. The parts of a phospholipid molecule. Phosphatidylcholine, represented schematically (A), in formula (B), as a space-filling model (C), and as a symbol (D). The kink due to the cis-double bond is exaggerated in these drawings for emphasis.
Figure 10-3. A lipid micelle and a lipid bilayer seen in cross-section. Lipid molecules form such structures spontaneously in water. The shape of the lipid molecule determines which of these structures is formed. Wedge-shaped lipid molecules (above) form micelles, whereas cylinder-shaped phospholipid molecules (below) form bilayers.
Figure 10-4. Liposomes. (A) An electron micrograph of unfixed, unstained phospholipid vesicles (liposomes) in water. The bilayer structure of the vesicles is readily apparent. (B) A drawing of a small spherical liposome seen in cross-section. Liposomes are commonly used as model membranes in experimental studies. (A, courtesy of Jean Lepault.)
Figure 10-5. A cross-sectional view of a synthetic lipid bilayer, called a black membrane. This planar bilayer is formed across a small hole in a partition separating two aqueous compartments. Black membranes are used to measure the permeability properties of synthetic membranes.
Figure 10-6. Phospholipid mobility. The types of movement possible for phospholipid molecules in a lipid bilayer.
Figure 10-7. Influence of cis-double bonds in hydrocarbon chains. The double bonds make it more difficult to pack the chains together and therefore make the lipid bilayer more difficult to freeze.
Figure 10-8. The structure of cholesterol. Cholesterol is represented by a formula in (A), by a schematic drawing in (B), and as a space-filling model in (C).
Figure 10-9. Cholesterol in a lipid bilayer. Schematic drawing of a cholesterol molecule interacting with two phospholipid molecules in one leaflet of a lipid bilayer.

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