An excerpt from my Microbiology book...

[timmerton120]

Peptidoglycan is a molecule unique to bacteria that provides rigidity to the cell wall. The gram-positive cell wall is composed of a relatively thick layer of peptidoglycan as well as teichoric acids. The gram-negative cell wall has a thin layer of peptidoglycan and an outer membrane, which contains lipopolysaccharide.

UHHHHHH....