The peptidoglycan cell wall is a branched polymer made of alternating NAG Iβ-D-N- acetylglucosamine,乙酰葡糖胺]and NAM IB-D-N- acetylmuramic acid,乙酰壁氨酸] residues. Polypeptide chains are attached to the nam residues and these vary depending on the strain of bacteria. The mechanism for cross-linkage is shown below. It is the terminal Dd-alanyl-D alanine residues of the polypeptide chain off of the nam residues that binds to the transpeptidase which cross-links that chain with the adjacent peptidoglycan strand. Penicillin binds at the active site of the transpeptidase enzyme that cross-links the peptidoglycan strands. It does this by mimicking the D-alanyl-D-alanine residues that would normally bind to this siteThe peptidoglycan cell wall is a branched polymer made of alternating NAG [β-D-N-acetylglycosamine,乙酰葡糖胺] and NAM [β-D-N-acetylmuramic acid，乙酰壁氨酸] residues. Polypeptide chains are attached to the NAM residues and these vary depending on the strain of bacteria. The mechanism for cross-linkage is shown below. It is the terminal D-alanyl-D￾alanine residues of the polypeptide chain off of the NAM residues that binds to the transpeptidase which cross-links that chain with the adjacent peptidoglycan strand. Penicillin binds at the active site of the transpeptidase enzyme that cross-links the peptidoglycan strands. It does this by mimicking the D-alanyl-D-alanine residues that would normally bind to this site