Bacterial Cell Wall

Article by Deepika

         Every small thing that is created by a nature is of one or the other use, therefore whenever we learn something basically we must know, 

1. What is it? and 

2. What is the use of it? 

           When we talk about cell wall, in simple words it can be defined as 'A surrounding layer of the cell which is tough, rigid & sometimes flexible' depending on the environment. Basically it functions to protect inner material of the cell like DNA & RNA (Genetic material), soluble enzymes, solutes, organelles etc. from the environment in which cell is growing or surviving. 

           Now coming to the bacterial cell walls, there is a fundamental difference in ultra structure (detailed structure) of cell wall of some bacteria on the basis of which these are classified in two groups,

 1. Gram Positive and 

 2. Gram Negative  

Note :- (Cells are divided in these groups with the help of staining procedure namely 'Gram staining' discovered by  scientist "Hans Christian Joachim Gram")

This difference in structure is associated with amount of peptidoglycan in cell wall. 

Made by Deepika

     Gram Positive cells have,

• Relatively thick cell wall.
• Major Component ( ~50%) is peptidoglycan .
• No lipids and often no proteins are found.
• Polymers such as Teichoic or Lipo teichoic acids are co-valently linked to peptidoglycan.

     Gram Negative Cells have,

• Cell envelope which consists of pair of membranes (Cytoplasmic & outer) with  thin layer of peptidoglycan.
• Outer layer consist of Lipo-polysaccharides (LPS) as well as lipids and proteins.
• LPS is located exclusively in the outer membrane.
• No teichoic or lipo teichoic acids are present. 

Cell walls of bacteria are made of different components such as proteins, lipo-proteins, lipids, polymers etc but peptidoglycan is the most important part of the bacterial cell wall.

    What is peptidoglycan?

• Peptidoglycan or murein is a sheet of polysaccharides, formed by cross linking glycan (poly or oligo-saccharides) chains with the help of peptide bonds or Glycan chains linked with peptide bonds forms peptidoglycan.
• This cross linking increases the strength and gives rigidity.
• Repeating units of peptidoglycan polymer is composed of two sugars,     

              1. N-acetyl-muramic-acid (NAM or MurNAc)

              2. N-acetyl-glucos-amine (NAG or GlcNAc) 

• Peptidoglycan is present in almost all bacteria except for Mycoplasmas and Archaebacteria.
• THIS IS UNIQUE TO BACTERIA.
• It has common architecture but variations are found in structural details. 
• It is ideal target for selective toxicity.

More details about ultra structure of cell walls will be covered in coming posts.....

Reference:- Madigan, Martinko, Dunlap, Clark. BROCK Biology of Microorganisms, 12th edition.