BACTERIAL MORPHOLOGY CONTD...
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.
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