Microbiology – Cell Wall of Gram Positive Bacteria.


  • A bacterial cell shows various parts and these parts have specific structure and functions.
  • These parts are separated by a rigid cell wall some parts are on the internal side of the cell wall and some parts are on the external side of the cell wall.
  • The parts present on the internal side of the cell wall are cell membrane, cytoplasm, nuclear region, reserve food material etc.
  • The cellular parts present on external to the cell wall are flagella, capsule and pilia.

Structure and function of Cell wall

  • The cell wall is the outer covering of bacterial cell in absence of capsule.
  • This cell wall is rigid in nature which imparts a proper shape to bacteria.
  • Cell wall encloses all internal parts of the cell.
  • On the basis of typical structure, composition and Gram staining they are classified

A)   Gram-positive bacteria.

B)   Gram-negative bacteria. Types of bacterial cell

Types of bacterial cell

A) The cell wall of Gram-positive bacteria.

  •  It is thick monolayered and accounts about 10 to 50% dry weight of cell.
  • Gram-positive cell wall is mainly composed of two important components.

     1. Peptidoglycan.    

     2. Teichoic acid.

1. Peptidoglycan  

Components of peptidoglycan of Gram-positive cell.

Components of Peptidoglycan of Gram positive cell wall
Components of Peptidoglycan of the Gram-positive cell wall.
  • Peptidoglycan is an important component of the cell wall.
  • It is also called as glycopeptide and mucopeptide.
  • Peptidoglycan is present almost in all bacteria except Halococcus and Halobacter.
  • The three main components of peptidoglycan are

a ) Glycan backbone strand.

b ) Tetrapeptide side chain.

c ) Cross bridges.

Structure of peptidoglycan of the gram positive cell wall.

Peptidoglycan structure of Gram positive cell wall
Peptidoglycan structure of Gram-positive cell wall

a ) Glycan backbone strand.

  • Glycan backbone strand contains a long chain of amino sugars these sugars are              N-acetylmuramic acid and N-acetyl glucosamine.
  • These sugars are linked to each other by Beta-1,4 linkage.
  • It is the unbranched chain.

b ) Tetrapeptide side chain

  • Tetrapeptide side chain consists of four amino acids in a particular sequence.
  • The sequence is L-alanine, D-glutamic acid, L-lysin, D-alanine.
  • Each N-acetylmuramic acid of glycan strand is linked to four amino acid by the peptide bond.
  • It is called as tetrapeptide side chain.

c ) Cross-linkage

  • When two adjacent tetrapeptide side chain is linked to each other by a glycan molecule called as cross-linkage.
  • The carboxyl group of fourth amino aid D-alanine of the side chain is linked to amino group third amino acid L-lysin of second tetrapeptide side chain.
  • The linkage of carboxyl group and the amino group is formed by five glycan molecules so called as a cross bridge.

2. Teichoic acid

  • Teichoic acid is the second most important component of the Gram-positive bacterial cell wall.
  • Teichoic acid is a water-soluble polymer.
  • It has repeating sugars.
  • Depending on types of repeating sugars teichoic acid is of two types.
  • They are Glycerol teichoic acid and Ribitol teichoic acid.

    Components of teichoic acid
    Components of teichoic acid of Gram-positive cell wall

1.Glycerol teichoic acid 

  • It is a long chain of glycerol 3 phosphate molecule.
  • These glycerol 3 phosphate are linked by phosphodiester bonds.

2. Ribitol teichoic acid.

  • It is a long chain of ribitol 5 phosphate molecule.
  • These are also linked by phosphodiester bonds.

Functions of the cell wall.

  • Cell wall gives rigidity, specific size and shape to the cell.
  • Cell wall protects the cell from osmotic pressure.
  • In high salt concentration cell wall protects the cell from the explosion.
  • It plays important role in growth and cell division.
  • Cell wall components such as lipopolysaccharides and teichoic acid provide an attachment site for bacteriophages.
  • The cell wall is a permeable membrane and because of its permeability, it provides transport of salts, water and other nutrients in the cell.


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