The cell wals of almost all the eubacteria are made up of peptidoglycan also called murein or mucopeptide cell wall. The glycan portion which forms the backbone of peptidoglycan is composed of alternating units of Amino sugars N-acetyl glucosamine (NAG) and N-acetylmuramic acid (NAM).

Introduction:
Muramic acid is a component of the cell walls of certain organisms. It is a unique characteristic of bacteria and blue-green algae, making it an important tool for their identification and classification.

Bacteria and Blue-Green Algae:
- Muramic acid is a major component of the peptidoglycan layer in bacterial cell walls. Peptidoglycan is a polymer made up of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) molecules.
- NAM contains a unique peptide chain that is cross-linked to neighboring NAM molecules, providing structural stability to the cell wall.
- This unique structure of the peptidoglycan layer, with its muramic acid content, is specific to bacteria and blue-green algae, allowing for their differentiation from other organisms.
- The presence of muramic acid can be detected through various staining techniques, such as the Gram stain, which is commonly used to classify bacteria based on their cell wall composition.

Green Algae:
- Green algae, on the other hand, do not possess cell walls made of peptidoglycan or contain muramic acid.
- Instead, they have cell walls composed of cellulose, which is a polysaccharide.
- Cellulose provides structural support to the cell and is also found in the cell walls of plants and some other algae.
- The absence of muramic acid in the cell walls of green algae is one of the distinguishing features between bacteria/blue-green algae and green algae.

Yeast:
- Yeast, which is a type of fungus, also does not contain muramic acid in its cell walls.
- Fungal cell walls are composed of a variety of polysaccharides, such as chitin or glucans, depending on the species.
- Chitin, a polymer of N-acetylglucosamine, is the primary component of the fungal cell wall and provides structural rigidity.
- The absence of muramic acid in yeast cell walls further differentiates them from bacteria and blue-green algae.

Conclusion:
In summary, muramic acid is present in the cell walls of bacteria and blue-green algae, but not in green algae or yeast. This unique component of the peptidoglycan layer allows for the identification and differentiation of bacteria and blue-green algae from other organisms.