Biochemistry: The Chemical Reactions of Living Cells, Volume 1 - D. Metzler 1980

Setting the Stage
Eukaryotic Cells
Cell Envelopes, Walls, and Shells

Like Bacteria, Cells of Higher Plants and animals are frequently coated with extracellular material. For instance, plant cells feature a rigid Cell wall containing abundant Cellulose and other polysaccharide polymers. Cells located on the outer surfaces of plants are often covered with a waxy layer. Animal cells are typically protected externally by Glycoproteins—complexes of CARBOHYDRATES and specific cell-surface Proteins. The intercellular space is filled with such "cementing substances" as Pectins in plants and hyaluronic acid in animals. Insoluble proteins—Collagen and Elastin—are secreted by Connective Tissue cells. Cells situated on surfaces (epithelial or endothelial) frequently border on the other side with a thin, collagen-containing basement membrane (Fig. 1-3). Often, As a result of the concerted action of various cell types, Inorganic Compounds are deposited, including calcium phosphate (in bones), calcium carbonate (eggshells and sponge spicules), silicon dioxide (diatom frustules), and so forth. Thus, METABOLISM takes place to a significant extent outside of cells.