Question

Explain the composition of the bacterial cell envelope including plasma membrane (Gram-&+), cell wall (Gram-&+) and outer membrane (only Gram-) as well as their individual components. Compare Gram+ and Gram- with regards to differences & similarities.

Answer 1

The cell envelope represents the outermost layer of the bacterial cell that has as general functions the protection of the cell, communication with the environment, maintenance of cellular shape, stability, and rigidity of the cell, as well as allowing appropriate metabolism, growth, and division of the cell. Important components of the cell envelope are carbohydrate-based and carbohydrate-containing macromolecules that contribute significantly to all of these functions, independent of which variation of the cell envelope occurs, i.e. Gram-positive, Gram-negative, mycobacterial, or archaeal. The Gram-positive, Gram-negative, and mycobacterial cell envelopes possess a general and typical architecture, whereas the archaeal cell envelope shows a broader variety of constructions and may be comprised of only a membrane. This chapter introduces the various types of bacterial cell envelope and their carbohydrate-related molecules, as well as the glycoprotein S-layers that can be found in all bacteria except mycobacteria. It describes the structures, syntheses, and functions of carbohydrate-containing macromolecules such as lipopolysaccharides, peptidoglycan, lipoteichoic acids, teichoic acids, capsule polysaccharides, and lipoarabinomannan.

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