Part I1. Antibiotics are organic chemicals that selectively kill bacterial cells

Question

Part I1. Antibiotics are organic chemicals that selectively kill bacterial cells (without harming eukaryotic cells). Many antibiotics work by attacking and disrupting different parts of the bacterial cell wall or membrane. For example, vancomycin is an antibiotic that has become critical for controlling penicillin-resistant bacteria. This large glycopeptide (molecular wt1449 Daltons) binds t peptidoglycan synthesis. ell wall precursors and interferes with The polymyxins are a group of antibiotics that are particularly effective as a topical antibiotic against skin infections. These large polypeptides (molecular wt. 1202 Daltons) can disrupt some bacterial membranes by binding preferentially to lipid A molecules. In the experiments below, different prokaryotic cells were grown in broth cultures in the presence or absence of an antibiotic (either vancomycin or polymixin). After 1 hour, cells were rinsed, and the percent of bacteria that survived was determined. with antibiotic without antiblotic 100 100 Bacillus E coli Methanoge n Bacilhus E coli Methanogen Using the data above, predict which experiment (A or B) was done using done using polymyxin, and explain your rationale. NOTE: Bacillus has a Gram (+) type envelope; E. coli has a vancomycin and which experiment was and Methanobacterium is an Archaca. (Hint: think about cell wall and membrane structure).

Explanation / Answer

Experiment A was conducted using polymyxin as E. coli shows the least growth in presence of this antibiotic. This antibiotic disrupts the cell membrane. Bacillus is least affected as it has a sturdy cell wall. Archae has a different membrane composition , hence it is least affected.

Experiment B was conducted using vancomycin as E. coli shows the least affected in presence of this antibiotic. This antibiotic disrupts the cell wall formation. Bacillus is most affected as it has a sturdy cell wall. Archae has a different membrane composition , hence it is least affected.

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