As discussed in class and in Chapter 6 of Lehninger, the antibiotic penicillin is a mechanism based inhibitor that blocks crosslinking of the peptidoglycan peptides by inactivating the enzyme transpeptidase. The antibiotic vancomycin, a "drug of last resort" for infections that resist other antibiotics, also blocks transpeptidase activity, but uses a mechanism different from that of penicillin. It acts in part by binding to the D-Ala D-Ala sequence on the peptide substrate. Some bacteria have a subtle mutation to their cell wall peptides that replaces D-Ala D-Ala with D-Ala D-Lac, where Lac is lactic acid. This mutation renders them resistant to vancomycin. Suggest a rationale for why the mutation might confer bacterial resistance to vancomycin, referring specifically to the difference in chemical structure created by replacing D-Ala with D-Lac in the peptide substrate. 2. The danger of influenza pandemics has led to interest in antivirals that limit the spread of influenza infection. The antiviral drugs Tamiflu (oseltamivir) and Relenza (zanamivir) bind to the influenza protein neuraminidase, a lectin that specifically recognizes the sugar N-acetylneuraminic acid and plays a key role in the infection cycle. As shown in Fig 7-30 of Lehninger 8th edition, the drugs bind strongly to neuraminidase because they mimic the N-acetylneuraminic acid. Unfortunately, oseltamivir-resistant viruses carrying mutated versions of neuramidinase have been isolated from human patients. Fig 7-30 explains the specific case of a His274Tyr mutation. Would you predict that influenza viruses carrying the His274Tyr mutation would also be resistant to zanamivir? Explain your answer.