Structures and functions of bacteria

Cell wall :
• The bacteria are surrounding by rigid cell wall. The principal structural component of cell wall is peptidoglycan(PG). It is complex polymers (polysaccharide and polypeptide).
• Most bacteria are classified according to reaction of Gram stain with components of cell wall , into two major groups : Gram positive and Gram negative bacteria.
• Cell wall of Gram positive bacteria consist of thick layer of PG and teichoic acid, whereas Gram negative bacteria have thin wall (less PG) and no teichoic acid. In addition to above, the Gram negative bacteria have complex outer layer consisting of outer cell membrane which is composed of lipopolysaccharide (LPS) and lipoproteins. The LPS is act as endotoxine( LPS not found in G+ve). The space between inner and outer membrane in gram negative is called periplasmic space(it is not present in cell wall of G+ve). The large amount of PG makes gram positive bacteria susceptible to antibiotic that inhibit cell wall synthesis (such as penicillins).
• All bacteria have cell wall exceptMycoplasma species lack cell wall.Most bacteria have rigid cell wall, except spirochetes have flexible cell wall.
• Function of cell wall;
1. Protection of internal structures.
2. It gives shape of the cell.
3. It contains toxic components to host cell.
4. Cell wall acts as somatic antigen(O-antigen) that is used in Laboratory diagnosis.