Cell Wall By Megarathan.J

❖ Gives shape to a cell ❖ provides rigidity to a cell ❖ 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 ★ % 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