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Cell Envelope  -

The cell envelope of the Gram-positive bacteria is much simpler in structure than that of the Gram-negative bacteria.

In the Gram negative bacteria. In the gram positive bacteria the cell envelope contains mainly the peptidoglycan and teichoic acids.

The peptidoglucan is a substituted sugar polymer found only in procaryotic organisms.

It consisits of acetylated aminosugars, n-acetyl glucosamine and n-acetylmuramic acid and small number of amino acids mainly D-glutamic acid, D and L-alanine

The adjacent peptide chains in a peptidoglycan may be cross linked by short peptides consisting of varying number of amino acids.

Variations in the structure of the peptidoglycan components occur and this has been used as a taxonomic tool.

The number of amino acids forming the cross link between two n-acetyl muramic acid residue can also vary .

Variations in the n-acetyl muramic acid are also known and these changes affect the compactness of the peptidoglycan considerably.

In the cell envelopes of Gram-negative bacteria two distinct layers are recognized.

One, a uniform inner layer about 2-3 nm wide and a thicker outer layer about 8-10 nm wide.

The outer layer is also called the outer membrane and the peptidoglycan is confined to the inner layer.

The outer membrane layer contains proteins. Lipoproteins and lipopolysaccbarides.