CELL ENVELOPE AND IT’S MODIFICATIONS

• · Bacteria that can take up gram stain is Gram positive bacteria and that does not take up gram stain is gram negative bacteria.
• · Cell envelope has 3 layered structure – outermost glycocalyx followed by cell wall and then plasma membrane. it acts as a protective unit.

• · Glycocalyx differs in composition and thickness among different bacteria.

• Slime layer- Made up only polysaccharides. It is a loose sheath.

2.Capsule- Made up of both polysaccharides and polypeptides. It is thick and tough.

• · Cell wall determines shape of cell and provides strong structural support to prevent bacterium from bursting and collapsing.
• · Plasma membrane is semi- permeable membrane interacts with outside world.
• · Mesosome is a special membrane structure formed by extension of plasma membrane into the cell. These are in form of vesicles, tubules, lamellae, help in cell wall formation, DNA replication and distribution to daughter cell.
• · Mesosomes help in respiration, secretion process, to increase the surface area of plasma membrane and enzymatic content.
• · In some prokaryotes called cyanobacteria, there are other membranous extensions into the cytoplasm called chromatophores which contain pigments.
• · Flagellum in bacterial cell helps in motility. Bacterium flagellum has 3 parts – filament, hook, and basal body. The filament is the longest portion and extends from the cell surface outside.
• · Pili and Fimbriae are also present; they do not play any role in motility. The pili are elongated tubular structures made of a special protein.
• · The fimbriae are small bristle like fibers sprouting out of the cell.