1.4.3 Inhibitors of nucleic acid synthesis

Differences between enzymes that carry out the synthesis of nucleic acids in eukaryotic and prokaryotic cells allow antibiotics to target these processes in bacteria.

For example, fluoroquinolones such as ciprofloxacin and levofloxacin (Figure 12) specifically inhibit bacterial enzymes that unwind the DNA double helix, separating the two strands so that the DNA can be copied. If the strands of DNA do not unwind and separate, bacterial replication is blocked.

Figure 12 The fluoroquinolone called ciprofloxacin. Fluoroquinolones all contain the chemical structure highlighted in red.

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This figure shows the chemical structure of the fluorquinolone ciprofloxacin. The structure highlighted in red is common to all fluoroquinolones. N = nitrogen, O = oxygen, H = hydrogen.

Figure 12 The fluoroquinolone called ciprofloxacin. Fluoroquinolones all contain the chemical structure highlighted in red.

Another class of antibiotics – rifamycins – inhibit RNA synthesis by binding to and inhibiting an enzyme called RNA polymerase. This enzyme transfers the instructions carried by genes to the intermediary molecule, mRNA. Interference in this process ultimately stops new proteins being made. Rifampicin is a commonly used rifamycin.