Radiolysis induces production of hydrogen peroxide in the cytoplasm. This is a consequence of which interaction?

• A. Target theory
• B. Direct effect
• C. Doubling dose
• D. Indirect effect

Answer: (D)

The key idea is indirect action: most radiation damage in cells comes from radiolysis of water rather than direct hits on DNA. When ionizing radiation passes through the cytoplasm, it breaks apart water molecules to form reactive species such as hydroxyl radicals, hydrogen atoms, and hydrated electrons. These short-lived radicals can diffuse and react with various cellular components, producing stable products like hydrogen peroxide. Hydrogen peroxide itself can diffuse and oxidize proteins, lipids, and nucleic acids, contributing to damage away from the original radiation track. So, the appearance of hydrogen peroxide in the cytoplasm is a classic result of indirect effects, driven by water radiolysis. The direct effect would be damage caused by the radiation depositing energy directly into DNA or other critical targets, while other terms like doubling dose relate to dose-response concepts and aren’t describing this molecular mechanism.