of external signals, including hormones and other ligands, and sites for
the recognition and attachment of other cells. Internally, plasma membranes can act as points of attachment for intracellular structures, in
particular those concerned with cell motility and other cytoskeletal
functions. Cell membranes are synthesized by the rough endoplasmic
reticulum in conjunction with the Golgi apparatus.
###### Cell coat (glycocalyx)
The external surface of a plasma membrane differs structurally from
internal membranes in that it possesses an external, fuzzy, carbohydraterich coat, the glycocalyx. The cell coat forms an integral part of the
plasma membrane, projecting as a diffusely filamentous layer 2–20 nm
or more from the lipoprotein surface. The cell coat is composed of the
carbohydrate portions of glycoproteins and glycolipids embedded in
the plasma membrane (see Fig. 1.3).

The precise composition of the glycocalyx varies with cell type; many