Step 1 First Aid Rapid Practice Test

Which therapy causes DNA double-strand breaks via free radical formation?

Radiation therapy Antibiotic therapy Vitamin C Antiviral therapy

Correct Answer:

Radiation therapy

Explanation:

Ionizing radiation damages DNA by generating free radicals inside cells. When radiation interacts with water, it splits molecules to create reactive oxygen species, especially hydroxyl radicals, which then attack DNA and produce breaks in both strands. Double-strand breaks are highly lethal to cells, so this is a primary way radiation therapy kills cancer cells. The other options don't rely on free-radical–mediated DNA damage in this context: antibiotics target microbial processes, vitamin C mainly acts as an antioxidant (though high doses can be pro-oxidant but aren’t used to induce DNA double-strand breaks in therapy), and antivirals inhibit viral replication rather than causing host DNA breaks via ROS.

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