Page 31 - MNU microbiology theoritical 2025

General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025

Cell wall

• A cell wall, not just of bacteria but for all organisms, is found outside of the cell

membrane.

• Most prokaryotes have a rigid cell wall.

• The rigidity of bacterial cell walls is due to a layer of peptidoglycan, a macromolecule

found only in bacteria

Function

- It protects the cell from mechanical damage and from osmotic rupture or lysis.

- It provides the definite shape of the bacteria.

- The cell wall is the basis for classification of bacteria according to the Gram

stain.

Structure of Peptidoglycan (murein layer)

• Peptidoglycan is a polysaccharide made of two glucose derivatives, N-

acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), alternated in

long chains.

• The chains are cross-linked to one

another by a tetrapeptide that extends

off the NAM sugar unit, allowing a

lattice-like structure to form.

• The four amino acids that compose

tetrapeptide are:

- L-alanine

- D-glutamine

- L-lysine or meso-diaminopimelic acid

(DPA)

- D-alanine.

General Microbiology & Immunology (PM 401) theoretical handbook Page 20