The Cell Wall Matrix
Chemical and morphological structures that comprise the envelope can no longer be dealt with as unrelated entities. The investigator must now ask how these structuresinteract dynamically—both temporally during their assembly and functionally during their operation. Loretta Leive, Bacterial Membranes and Walls, 1973
Cell walls of prokaryotes aremore than just structural frameworks for the cells. The cell wall in bacteria is a highly complex region that contains different molecular components in addition to the peptidoglycan and the S-layer. InGram-negative bacteria, the cell wall encompasses an outer membrane that is unique in that it has a highly organized structure and functions as a permeability barrier for many compounds. Varioustypes of ionized molecules are attached to the peptidoglycan of Gram-positive bacteria and they distribute charges within the cell wall as well as at the surface. These extra components have diverse butspeciﬁc roles and may even enable bacteria to grow in hostile chemical environments. From various research reports concerning the cell walls of archaea, it can be inferred that these organisms alsocontain molecules in addition to those that are responsible for cell shape and cell stability. This chapter examines the chemical structure and biological functions of polysaccharides, acidic polymers,and proteins in the cell walls of prokaryotes. On the basis of the Gram-staining reaction, two distinct types of prokaryotes are differentiated and analysis of the cell wall of these two groups oforganisms indicates a fundamental difference in chemical composition. Besides providing structural rigidity for both Gram-positive and Gram-negative bacteria, the cell wall has additional functions thatinclude the following: (1) transports nutrients from the environment to the cell membrane; (2) enhances virulence of pathogens by attaching microbial cells to host animal cells through speciﬁc...