This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General, Subject name: Microbiology
Which one of the following antibiotics inhibits the final peptide bond between d-alanine and glycine? 
Select and explain. 
A. Penicillin, B. Amdinocillin, C. Amphotericin, D. Chloramphenicol
A: Penicillin
Answer: A: Penicillin 
Explanation: The antibiotics in these questions have significantly different modes of action. Recent evidence suggests that while penicillin inhibits the final cross-linking of the cell wall, it also binds to penicillin-binding proteins and inhibits certain key enzymes involved in cell-wall synthesis. The mechanism is complex. Amdinocillin, although classified as a penicillin, selectively binds to penicillin-binding protein-2 (PBP-2). Binding to PBP-2 results in aberrant cell-wall elongation and spherical forms, seen when E. coli, for example, is exposed to mecillinam.