The bacterial cell wall contains a common and important component called peptidoglycan, which is only found in prokaryotes. Peptidoglycan is a polymer of alternating n-acetyl-glucosamine (NAG) and n-acetyl-muramic acid (NAM) which are linked by a covalent bond. Each NAM contains a chain of 4 amino acids. This amino acid chain crosslinks the adjacent polymers of amino sugars forming a lattice network around the exterior of the cell. It is this lattice that determines the shape of the cell (coccus, rod, or spiral). The lattice diversity results from a bridge being formed from different amino acids within the lattice. For example Staphylococcus may have the serine and glycine amino acid form a bridge as opposed to multimpl glycine residues. The cell wall of gram positive bacteria is made of up of 90% peptidoglycan. Most gram positive bacteria have teichoic acid in their cell wall as well. This is what creates the overall negative charge.
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