The bacterium Bacillus anthracis, known as anthrax, causes an often fatal disease that is also called anthrax. On November 7, 2001, the Senate Majority Leader's office received an anthrax-tainted letter. More than 30 Senate workers showed signs of exposure. The U. S. Centers for Disease Control and Prevention (CDC) recommends that anyone who might have been exposed to anthrax begin treatment with the antibiotic ciprofloxacin, a DNA-synthesis inhibitor.
Ciprofloxacin inhibits DNA gyrase, a bacterial topoisomerase that cuts DNA ahead of the replication fork, winds the DNA in a direction that relieves the twists added during DNA synthesis, and then reseals the DNA. In ciprofloxacin-treated bacteria, newly synthesized DNA is found in fragments. Based on this evidence, what activity of DNA gyrase is likely to be inhibited by ciprofloxacin?

Ciprofloxacin inhibits DNA gyrase, a bacterial topoisomerase that cuts DNA ahead of the replication fork, winds the DNA in a direction that relieves the twists added during DNA synthesis, and then reseals the DNA. In ciprofloxacin-treated bacteria, newly synthesized DNA is found in fragments. Based on this evidence, what activity of DNA gyrase is likely to be inhibited by ciprofloxacin?

a. DNA polymerase activity
b. ligase activity
c. primase activity
d. helicase activity