Gram Negative
Gram negative bacteria cells, unlike gram positive cells, cell walls consist mostly of outer membrane, not peptidoglycan, which is responsible for the strength of the cell. It’s like a second lipid bilayer but composed of lipid and polysaccharide, instead of protein and phospholipid. It’ made of one layer of lipopolysaccharide layer or LPS and the other is peptidoglycan. The polysaccharide in the lipopolysaccharide is made from O- specific polysaccharide and core polysaccharide. A unique characteristic of the lipopolysaccharide is its toxicity to animals. The lipid portion of the LPS layer is made of Lipid A, which contains an endotoxin that is responsible for its toxicity to animals. Another unique characteristic of the LPS layer in gram negative bacteria would be that the LPS acts like an anchor and types peptidoglycan to itself, creating a bilayer distinct from the cytoplasmic membrane. Between the cytoplasmic membrane and the outer membrane, is the periplasm. This space is filled with fluid that has a gel- like consistency due to all the proteins located there. Its purpose it to make sure that proteins that have activities outside the membrane do not diffuse away. The outer membrane is semipermeable to small molecules due to the presence of porins. It will not let in large molecules and proteins. Microbiologists are able to differentiate between gram positive cells and gram negative cells due to gram staining. Due to the structure of gram negative bacteria cell walls, it does not retain the purple color of the crystal violet iodine complex that forms in the cell, due to it being able to be extracted by alcohol. Thus it has to be counterstained with safranin, and appears pink. The thin layer of peptidoglycan is responsible for this occurrence.