7) Ciprofloxacin belongs to a family of antibiotics called quinolones. Researche
ID: 145263 • Letter: 7
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7) Ciprofloxacin belongs to a family of antibiotics called quinolones. Researchers studying three quinolones added them separately to growing bacteria and then examined DNA synthesis rates over time compared to a culture not exposed to any drug. The results are shown in the figure below. 1601 Drug addition o No drug added 9 100 80 Norofloxacin 60 Ciprofloxacin 40 Naladxic acid et 20T -10 0 10 20 30 40 Time after drug addition (min) Source: Fournier, B, et al. 2000. Antimicrobial Agents and Chemotherapy 44:2160-2165 A) Which antibiotic inhibited DNA synthesis least rapidly? B) would you expect similar results if you were testing eukaryotic cells, such as human cells, in the presence of this antibiotic? Why or why not?Explanation / Answer
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A- According to the graph the Norfloxin is least rapidly ( slow, more time) inhibiting the rate of DNA synthesis as compared to the other two drugs. It can be clearly seen in the graph that after exposing the cells the DNA synthesis line drops least for norfloxin, it is taking more time whereas as Nalidixic acid reduces DNA synthesis rate rapdily, taking less time.
Nalidixic acid is faster in inhibiting the DNA synthesis than ciproflaxin and norfloxin. Ciprofloxin is intermediate in action.
Quinolones are group of antibiotics which are against DNA synthesis in bacterial cells, mycobacteria and also mycoplasma.
The target enzymes for quinolones are topoisomerase II also called DNA gyrase. Topoisomerase relaxes supercoiled DNA and causes transient breaks and rejoins phosphodiester bonds.
B- If similar experiments are carried out using human cells the result will not be same because quinolones are specific for bacterial topoisomerase II which is also present in eukaryotic cell but differ in the location as well as the subclass which reduces its specifity if applied to human cells.
Prokaryotes have type II topoisomerase with type I and II subclass.
Eukaryotes have only typeII subclass.
Cellular origin, and distribution also vary.
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