The bacteria which take purple color are called gram positive bacteria and those which take up pink color are gram negative bacteria. When these bacteria were counter stained with safranin it was observed that some of the bacteria retained purple color and others take up pink color. On washing them with acetone, few bacteria became purple where as others remained colorless. In 1884, a scientist named Gram tried to stain the bacterial cells with crystal violet and iodine solution. Bacterial cell wall contributes to the pathogenicity in other words, disease causing ability of bacterial cells.The cell wall helps in keeping out certain molecules which may be toxic. The cell keeps moving from one environment to other and moreover as water can freely move from both the cell membrane and the cell wall, the cell is at risk of osmotic imbalance thereby causing osmotic lysis of the cell. Cell wall protects the cell from the osmotic lysis.It helps maintain the cell shape, thereby helping the cell to grow, reproduce, obtain nutrients and also move about.The main function of the bacterial cell wall is to provide overall strength to the cell.The inclusion of both L and D amino acids in the structure provides protection from digesting effect of proteases. Whereas in Gram negative bacteria and myxobacteria, L-lysine is replaced by diaminopimelic acid (DAP). The four amino acids that compose the tetra peptide are: L-alanine, D-glutamine, L-lysine and D-alanine in Gram positive bacteria and actinomycetes. The NAG and NAM chains are cross-linked to one another by tetra peptides that extend off the NAM unit forming a lattice-like structure. This linkage gives stability and strength to the cell wall. The alternating units of NAG and NAM are linked together by a glycosidic bond (β-1, 4 linkages). Both NAG and NAM form the back bone of the cell wall structure. One of these two is NAM (N-Acetyl Muramic acid) and the other is NAG (N-Acetyl glucosamine). The saccharide component of the cell wall has alternating repeating units of two amino sugars related to glucose. Thus a bacterial cell wall is glycopeptide which is also known as peptidoglycan. Chemical composition of the bacterial cell wallĬell wall is composed of two polymers, one consisting of saccharide subunits and the other consisting of amino acid subunits. Bacterial cell has the ability to retain their original shape when subjected to very high pressures, due to the rigidity of the cell wall. Hence, the main function of the cell wall is to prevent the cell from expanding and eventually bursting in the hypotonic environments. Most of the bacteria live in hypotonic environments and tend to take up water due to the variation in the osmotic pressures between the bacterial cells and the existing environment. Structures internal to the cell include cytoplasmic membrane and all other cytoplasmic inclusions.Ĭell wall is a very rigid structure which provides support and gives shape to the cell. Structures external to the cell wall include flagella, capsules and sheaths. Some of the structures are confined only to certain species and some other structures act as the characteristic features of certain species. A Bacterial cell under an electron microscope reveals many components, some of which are external to the cell wall and some are internal to the cell wall.
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