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