How do fluoroquinolones block bacterial DNA replication?

Question

1. Fluoroquinolones inhibit the synthesis of precursor bases.
2. Fluoroquinolones bind to enzymes of bacterial DNA replication, blocking the relaxation and migration processes.
3. Fluoroquinolones inhibit topoisomerase I so that DNA cannot be repaired.
4. Fluoroquinolones bind with the enzyme DNA polymerase, blocking the replication of the DNA process.

Answer 1

Correct Answer: 2
Rationale 1: Cytarabine and fluorouracil (chemotherapeutic agents) resemble nucleotides and are mistakenly incorporated into newly formed DNA strands.
Rationale 2: Fluoroquinolones bind to enzymes gyrase and topoisomerase, blocking the relaxation and migration processes of bacterial DNA replication.
Rationale 3: Certain antineoplastic agents work by inhibiting the repair of DNA. Fluoroquinolones bind to enzymes DNA gyrase and topoisomerase IV, preventing bacterial DNA replication.
Rationale 4: Acyclovir inhibits the DNA polymerase, preventing replication of DNA into two daughter strands.
Global Rationale: The fluoroquinolone antibiotics act on two enzymes in the DNA replication process. First, they bind to DNA gyrase, inhibiting its ability to relax the supercoiling of the bacterial DNA. When the replication enzymes reach an area still in a supercoiled state, replication terminates. A second mechanism is binding to topoisomerase IV. When this occurs, the two daughter DNA strands cannot migrate to opposite sides of the cell, and division cannot be completed. They do not inhibit synthesis of precursor bases, bind with the enzyme DNA polymerase or block repair as is the mechanism of action of some other classes of drugs.