Cell wall
Cell wall is tough and rigid structure surrounding bacterium like a sheel.
Bacterial Cell wall contains network of peptidoglycan chains.
Types of cell walls of bacteria
Two types of cell walls of bacteria-
1. Gram-Negative cell wall
2. Gram-Positive cell wall
1. Cell wall of Gram Positive Bacteria
1. Peptidoglycan
Gram Positive Bacteria usually have much greater amount of peptidoglycan in their cell wall (16-80 nm) than gram negative bacteria (2 nm).
2. Teichoic acid
Gram positive cell wall contains teichoic acid. Teichoic acid helps to hold peptidoglycan chain together.
Teichoic acid absent in gram negative bacteria.
Teichoic acid act as surface antigen, protect bacteria from thermal injury of Gram Positive Bacteria.
2. Cell wall of Gram negative bacteria
Cell wall of Gram negative bacteria has no teichoic acid and thin peptidoglycan layer.
This is why, it loses crystal violet stain during gram staining.
Lipoproteins layer
Outer portion of cell wall consist of an outer membrane, not found in gram positive.
Lipoprotein layer connects peptidoglycan to outer membrane.
Outer membrane
Contain certain proteins named outer membrane proteins. These are target sites for phages, antibiotics.
Lipopolysaccharides (LPS)
LPS constitute endotoxin of gram-negative bacteria.
Lipopolysaccharide composed of -
1. Lipid A; Lipopolysacchaide layer consist of lipid A.
2. Polysaccharide; which attach to polysaccharide.
3. Polysaccharide O antigen; polysaccharide determines major surface antigen, O antigen.
4. The periplasmic space is space in between the inner and outer membranes, provide resistance to gram negative cells from antimicrobial agent dyes, disinfectant and lysozymes.
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