Page 76 - Atlas of Histology with Functional Correlations
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FIGURE 2.2 ■ Composition of cell membrane.
MOLECULAR ORGANIZATION OF THE
CELL MEMBRANE
The lipid bilayer of the cell membrane has a fluid consistency, and as a result,
the compositional structure of the cell membrane is characterized as a fluid
mosaic model. The phospholipid molecules of the cell membrane are distributed
as two layers. Their polar heads are arranged on both the inner and outer
surfaces of the cell membrane. The nonpolar tails of the lipid layers face each
other in the center of the membrane. Images of cell membrane viewed with the
transmission electron microscope, however, appear as three distinct layers,
consisting of outer and inner electron-dense layers and a less dense or lighter
middle layer. This discrepancy is due to the osmic acid (osmium tetroxide) that
is used to fix and stain tissues for electron microscopy. Osmic acid binds to the
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