Bacterial cell wall | Its Structure and Function
The bacteria cell wall is an important structure which is rigid and non living envelop around the cell.
It is present just above the cell membrane and gives a specific shaped to the cell.
Because of this cell wall, bacteria can survive harshest environmental conditions like the drought, heat, chemical exposure, pressure, etc.
If the harsh conditions persist, then bacteria cell wall forms endospores. These spores are dormant and give rise to new bacteria when conditions improve. Thus cell wall makes the bacteria immortal.
The bacterial cell wall structure:
The bacterial cell wall is made of mucopolysaccharides and mucopeptides. The muco peptide is a polymer of N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG). Besides them, an aminoacid called diaminopimetic acid and a polysacharide called muramic acids arepresent in cell wall.
Structure of the bacterial cell wall is classified into two types. The one present in gram-positive bacteria and the other present in gram-negative bacteria. Below you can see the images for structures of two cell walls.
Gram-positive bacteria cell wall:
This cell wall of this bacteria is very rigid. It has thick layer of peptidoglycan. Peptidoglycan is a combination of protein and carbohydrate molecules.
Because of this high amount of peptidoglycan layer, the bacteria show blue color when stained with gram stain. The layer does not take up the saffron color of stain, unlike gram-negative bacteria. This difference in cell wall structure makes the bacteria susceptible to antibiotics which act on the cell wall.
Gram Negative bacteria cell wall:
This cell wall is entirely different from the one above. The amount of peptidoglycan layer is very much low.
a) The upper most layer is made of lipoproteines.
b) The second layer is made of lipopolysacharides
c) The bottom layer covering cell membrane is made of mucopeptides.
Besides it also has phospholipids teichoic acid, etc.
This cell wall when stained with grams stain, it attains saffron color. The lipopolysaccharide layer holds the saffron dye in the stain and is responsible for the color.
Functions of bacteria cell wall:
- It helps to provide a fixed shape to the cell.
- It facilitates the movement of gases and water into and outside the cell.
- It prevents the cell from getting dried during extremely hot conditions.
- It protects from chemicals and other harsh condition of the environment. Hence we use heat sterilization to kill bacteria.
- The outer most layer also called S-layer helps the bacteria to escape from phagocytosis by host immune cells.
For the man, it is an essential target in health care to cure bacterial infections. Humans target them by giving drugs (antibiotics) which destroy the cell wall. Since human cells don’t have a cell wall, they are unaffected. Similarly, due to the difference in gram +ve and gram -ve bacteria, an antibiotic with specificity to one type of bacteria can be given.
Thus the presence of cell wall is good for bacteria but also provides a safe option for human health care.
Further, cell wall is a characteristic feature of plants. So, some scientists classify bacteria under the plant kingdom. But unlike plants, the contents of the wall are entirely different.