Differentiate between prokaryotic and eukaryotic ribosomes. Briefly describe the structure of the peptidoglycan layer. Differentiate between Gram-negative cell wall and Gram-positive cell wall. Why is oxygen toxic to obligate anaerobes?

The peptidoglycan layer is a rigid mesh-like structure found in the cell walls of most bacteria. It is primarily composed of alternating units of two amino sugars: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). These sugar units are linked by $\beta$-(1,4) glycosidic bonds to form linear glycan chains. Adjacent glycan chains are cross-linked by short peptide bridges attached to the NAM residues, providing strength and structural integrity to the bacterial cell wall.