Cell Wall
By Megarathan.J
❖ Gives shape to a cell ❖ provides rigidity to a cell❖ 10-25 nm thick❖ 20-30% of the dry weight of the cell❖ Permeable to the passage of liquid
nutrient material❖ Antigenic
Properties :
Structure :➔ Made of peptidoglycans➔ Peptidoglycans are also known as
mucopeptide or murein➔ It has 3 Components:
◆ Backbone● N-Acetyl Glucosamine● N-Acetyl Muramic Acid
◆ Set of Identical Tetrapepide bridge◆ Set of Pentapeptide Cross Bridge
Structure (cont.):
All bacterial species have the same backbone, but the Tetrapeptide and the Pentapeptide cross bridges vary with each species.
Gram Positive Cell Wall:
★ 80nm thick★ 50-90 % of the dry weight of the cell wall.★ Peptidoglycan- several layers thick★ Teichoic acid- two types
○ Cell wall○ Membrane
★ Antigens- ○ proteins○ polysaccharides
Gram Negative Cell wall :
Thinner than Gram Positive cell wall but more complex Structurally Contains:
Peptidoglycan Lipoprotein Lipopolysaccharide Outer Membrane
Gram Negative Cell wall (cont.):
Thinner peptidoglycan layer – one layer.
Outer membrane is outer to Peptidoglycan layer.
Outer membrane is anchored to the
peptidoglycan by a lipophilic lipoprotein.
Structure similar to cell membrane – phospholipid bilayer.
Proteins – Outer Membrane Proteins and Porins are embedded in Outer membrane
Gram Negative cell wall (cont.):
Special channels – consisting of Porin proteins permit the passive diffusion of low molecular weight hydrophilic compounds –sugars, amino acids and ions.
Large antibiotic molecules cannot penetrate outer membrane easily.
This is responsible for Antibiotic Resistance.
Gram Negative Cell Wall (cont.):
Acid Fast Cell Wall
Mycobacterium & Nocardia have a gram
positive structure
They have a waxy layer of glycolipids and
fatty acids bound to the exterior of the cell –
makes them acid fast