Читать книгу An Introduction to Molecular Biotechnology - Группа авторов - Страница 30

Some cell types are enclosed by a cell wall:

 Bacterial cells are surrounded by a peptidoglycan layer (Figure 3.27). Gram‐positive bacteria (e.g. members of the Bacillus genus) have a thick cell wall, which borders immediately to the outside milieu, whereas in Gram‐negative bacteria (e.g. Escherichia coli), a thin cell wall is surrounded by a second lipopolysaccharide membrane as an outer shell vfd (Figure 1.1). The outer membrane has porin proteins that allow the entry of food molecules. The cell wall is an important target structure for antibiotics – penicillins and cephalosporins inhibit cross‐linking of linear glycopeptide strands. Bacitracin inhibits the synthesis of polyprenol, which is a prerequisite for the formation of a murein sacculus.

 Fungal cells are surrounded by a chitin wall.

 Plant cells have cell walls consisting of cellulose, hemicellulose, and pectin. They can be enzymatically digested by cellulases, producing protoplasts, which are useful for plant biotechnology.

Figure 3.27 Schematic view of bacterial cell walls. (a) Gram‐positive bacteria. (b) Gram‐negative bacteria.

Cell walls serve mostly to protect and stabilize cells. They also ensure against lysis from osmotic swelling, when have taken up too much water through osmosis.