Morphological and Histochemical Aspects of Glycoproteins at the Surface of Animal Cells

Abstract

Morphological and Histochemical Aspects of Glycoproteins at the Surface of Animal Cells This chapter emphasizes on the microscopic evidence for a carbohydrate-rich layer at the cell surface. There is a description and critical analysis of the histochemical techniques involved in that carbohydrate-rich layer's localization. According to Danielli-Davson model , the plasma membrane consists of a bimolecular lipid layer in which the polar heads are directed outward, coated on both inner and outer surfaces with protein. When the cell surfaces of animal cells are examined in the electron microscope after osmium or permanganate fixation, the so-called unit membrane in which two electron-dense layers are separated by a lighter zone. Recent data derived chiefly from cell electrophoresis and immunological studies performed on red blood cells or ascites tumor cells indicate that sialic acid-containing glycoproteins are important constituents of the cell surface. Furthermore, the improvement of preparative techniques for the electron microscope has permitted the visualization of a filamentous or globular material on the outer surface of the plasma membrane. The use of histochemical techniques for the detection of polysaccharides at the light and electron microscope levels has led to the identification of a carbohydrate-rich layer at the surface of most animal cells.