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Bacterial cell walls are made of peptidoglycan (also called murein). on the basis of their bacterial cell wall the bacteria are of two types. The first one is gram positive bacteria and second one is gram negative bacteria. The difference between these two are as follow.
Composition of Peptidoglycan
| Gram Positive Bacteria | Gram Negative Bacteria |
| Four amino acids are present in gram positive bacteria. | Along with three amino acids, gram positive bacteria have fourth one. |
| 1: L- alanine
2: D-alanine 3: D- gultamic acid 4: L- lysine
|
1: L- alanine
2: D-alanine 3: D- gultamic acid 4: Diamineopimelic acid (DPA)
|
Gram Positive and Gram Negative Bacterial Cell Wall
Gram Positive Bacterial Cell Wall
Now we have to see. How these components of peptidoglycan are joined together (linked together)?
- First of all, we are discussing the Gram Positive Bacterial cell wall arranging material.
- The components which are shown here is glycan portion. Which is made up of modified sugars present in chain through alternative arrangement. It means in glycan portion, there is formation of chain portion. This chain portion arrangement is amino acids and are known as Tetrapeptide Chains to NAM.
- Tetrapeptide chains are linked together by chains of five amino acids (pentapeptide chain).
- Sugars form back bone in gram positive bacteria that are linked with the help of amino acids chains.
- So, organization of gram positive bacterial cell wall has completed.
Gram Negative Bacterial Cell Wall
In gram negative, bacteria or bacterial cell wall:
- Again, sugars are associated in alternative manners (one NAM and one NAG).
- Again, attachment of tetrapeptide chain to NAM.
- Pentapeptide chain is absent in gram negative bacteria. So, there is direct linkage between tetrapeptide chain. Therefore, we can conclude one difference there.
Difference Between Gram Positive and Gram Negative Bacterial Cell Wall
Difference between gram positive and gram negative bacteria is in the following table.
|
Gram Positive Bacteria |
Gram Negative Bacteria |
| Teichoic acid
It is a thread like structure composed of carbohydrates, alcohol and phosphate. They have antigenic characteristics. |
Teichoic acid
It is absent in gram negative bacteria. Antigenic characteristics in gram negative bacteria are develop by lipopolysaccharides. |
| Porin Protein
It is absent in gram positive bacteria due to absence of lipopolysaccharides. |
Porin Protein It is present in gram negative bacteria (Intrinsic proteins with pores). They involve in uptake of hydrophilic compound with lower molecular weight |
| Peptidoglycan is thick (150-200 A) | Peptidoglycan is thin (70-120 A) |
| Only single membrane system | Double membrane system |
| Cell wall of gram positive bacteria composed of only one layer of Peptidoglycan.
So, cell wall of this bacteria is composed of single one component peptidoglycan. Therefore, cell wall is Homogenous. |
Cell wall of gram negative bacteria composed of two layers: Lipopolysaccharides (Made up of Lipid Bilayer). Peptidoglycan (Inner)
|
| There is indirect linkage of two tetrapeptides with the help of pentapeptide. | There is direct linkage of two tetrapeptides due to absence of pentapeptide chain. |
| More linkages are present. Therefore, network of cell wall is strong. | Less linkages are present |
| In these bacteria, one phospholipid bilayer is present below cell wall in the form of plasma membrane. | In these bacteria, there are two layers of phospholipids. One in the form of Plasma Membrane (inner membrane). Second one in the form of LPS (Lipopolysaccrides) outer membrane. |
|
Effect of Lysosome Lysosome eats the peptidoglycan of cell wall. The only thing remain is then plasma membrane and cytoplasm. Simply the plasma membrane and cytoplasm is collectively called as protoplast |
Effect of Lysosome
In case of gram negative bacteria there is partial digestion of peptidoglycan layer. The partially digested cell is also known as Sphaeiplast (Spheroplast). |