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Gram Positive and Gram Negative Bacteria It is a well-known fact that bacterial cells, like plant cells, are surrounded by a cell wall. However, few people know that their cell walls are quite different. Bacterial cell walls are made up of polysaccharide chains linked to amino acids. At the same time, plant cell walls are made up of cellulose, which contains no amino acids.
In the same way, bacterial cell walls themselves differ from one another. Scientists distinguish two types of bacteria cells, gram-negative and gram-positive, which are somewhat different due to some of their characteristics. There are two major types of walls: gram positive and gram negative. The cell wall of gram positive bacteria is composed of numerous polymer layers of peptidoglycan connected by amino acid bridges. The peptidoglycan polymer is made of some variable sequence of N-acetyl glucosamine and N-acetyl-muraminic acid. It is quite easier to just remember the following abbreviation NAG and NAMA.
Each peptidoglycan layer is linked to the other by a bridge made of amino acids and amino acid derivatives. However, the particular amino acids may alternate among different species. The connected peptidoglycan molecules organize a network which covers the cell like a grid. Besides, 90 % of the gram positive cell wall is comprised by peptidoglycan. On the contrary to the gram positive bacteria, the cell wall of gram negative bacteria is much thinner, consisting of only 20 % peptidoglycan. Gram negative bacteria also have two unique sections which surround the outer plasma membrane.
They are the periplasmic space and the lipopolysaccharide layer. The periplasmic space separates the outer plasma membrane from the peptidoglycan layer. It holds proteins destroying potentially dangerous foreign matter present in this space. The lipopolysaccharide layer can be seen next to the exterior peptidoglycan layer. It is a phospholipid bilayer construction which is similar to that in the cell membrane and is attached to the peptidoglycan by lipoproteins. The lipid portion of the LPS contains a toxic substance, called Lipid A.
The latter is responsible for most of the pathogenic affects associated with harmful gram negative bacteria. Polysaccharides extending out from the bilayer also contribute to the toxicity of the LPS. The LPS, lipoproteins, and the associated polysaccharides form what is called the outer membrane. By the way, it is important to keep in mind that the cell wall is not a regulatory mechanism like the cell membrane. It is certainly a porous structure. Yet it is not selectively pervious and will obviously let anything pass that can fit through its gaps.
Unlike gram negative, gram positive bacteria have a violet color in gram staining. Due to high lipid and low peptidoglycan content of the cell wall of gram negative bacteria, the primary crystal-violet escapes from the cell when the decolorizes is added. This is because primary stains like to bind with peptidoglycan a substance the gram negative cell has very little of. Gram negative bacteria often become a cause of a lot of problems because many species are pathogenic. This pathogenic capability is usually associated with certain components of their cell walls, particularly the lipopolysaccharide or endotoxin layer.
It is enough to remember the Black Plague which made a third of the population of Europe to be wiped out. It happened due to the tiny gram negative rod, Yersinia pestis. Most enteric or bowel related diseases can also be related to this group of bacteria. As it has been mentioned above, gram positive bacteria are characterized by their blue-violet color reaction. Such kind of reaction happens when crystal-violet complexes with the iodine mordant. Adding the decolorizes causes a slow dehydration of the crystal-violet / iodine complex.
This can be observed due to the closing of pores running through the cell wall. Being still present in the cell, the crystal-violet maintains the cell's blue-violet color. There is a distinguishing factor among gram positive bacteria: approximately 90 % of their cell wall is made of peptidoglycan. At the same time, a gram positive bacteria can have more than 20 layers of peptidoglycan stacked together to form the cell wall.
That is a quite thick structure. Common examples of gram positive cells are Staphylococcus aureus and Streptococcus cremoris. These bacteria are used in dairy production. The bacterial cell wall is a unique structure which surrounds the cell membrane. The cell wall is not present in every bacterial species. However, it is extremely important as a cellular component.
The cell walls of all existing bacteria are not completely identical including the cell walls of gram positive and gram negative bacteria. In fact, it is very important to realize the difference because cell wall structure is one of the most important factors in bacterial species analysis and differentiation. Bibliography: Button, Edward J. Unusual Microorganisms: Gram Negative Fastidious Species. New York, NY: M. Dekker, 1983.
Gram Negative Bacteria. An Australian website about Gram Negative bacteria. web 11 March 1998. Gram Positive Bacteria. An Australian website about Gram Positive bacteria. web 11 March 1998.
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Research essay sample on Gram Positive And Negative Bacteria
