BACTERIAL MORPHOLOGY CONTD...

A) STRUCTURE EXTERNAL TO CELL WALL

4)  Cell Wall:  1) Gram Positive Cell Wall : Gram Positive cell wall has greater amount of peptidoglycan (ie around 25 nanometer) & may account for 50% or more of total dry weight of cell. Besides, peptidoglycan gram positive cell wall contains Teichoic acid. It helps to link the peptidoglycan layer & provides negative charge to the cell wall. Though, much gram positive cell wall contains very little lipid but Mycobacteria & Cornyebacterium spp  & other are rich in lipids called Mycolic acid.

                                                      FIG:  B= GRAM NEGATIVE CELL WALL A= GRAM POSITIVE CELL WALL
                                             

             

2).Gram Negative Cell Wall:  Wall of Gram negative bacteria are more complex than those of Gram positive bacteria. It comprises lesser amount of peptidoglycan (2 nm to 3 nm) thick,which  accounts 10% of wall weight. The outer membrane is absent in Gram positive bacteria. The outer membrane is bi-layered structure consisting of phospholipid, proteins,  & lipopolysaccharides(LPS). LPS has toxic property & is also known as Endotoxin.  LPS is absent in gram positive bacteria & comprised of three parts: lipid A, Core Polysaccharide, O Side chain or O Antigen.
                             The protein part contains unique protein called porins which contains to  the passage of small molecules. Periplasmic space lies between outer membrane & cell membrane & it is filled with periplasm that contains digestive enzymes & transfer proteins.


                                          FIG: GRAM NEGATIVE CELL WALL 

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