Free radicals are produced as a result of radiolysis. Which interaction is responsible?

Free radicals are produced as a result of radiolysis. Which interaction is responsible?

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

Answer: (D)

The key idea is that most radiation damage in biology comes from the indirect effect, produced by radiolysis of water. When ionizing radiation passes through a cell, it preferentially ionizes and excites water molecules, which are abundant in the cytoplasm and nucleus. This radiolysis creates reactive free radicals such as hydroxyl radicals and hydrogen atoms. These radicals diffuse and attack DNA and other critical biomolecules, causing breaks and base damage without the radiation having to hit the DNA directly. Because water is so plentiful, the indirect route accounts for the majority of the initial chemical damage from many types of radiation, especially low LET radiation. Direct effect would require the radiation to interact with DNA itself, which is less likely in a water-rich environment, and the other terms refer to different concepts (not the chemical process producing radicals).

The key idea is that most radiation damage in biology comes from the indirect effect, produced by radiolysis of water. When ionizing radiation passes through a cell, it preferentially ionizes and excites water molecules, which are abundant in the cytoplasm and nucleus. This radiolysis creates reactive free radicals such as hydroxyl radicals and hydrogen atoms. These radicals diffuse and attack DNA and other critical biomolecules, causing breaks and base damage without the radiation having to hit the DNA directly. Because water is so plentiful, the indirect route accounts for the majority of the initial chemical damage from many types of radiation, especially low LET radiation. Direct effect would require the radiation to interact with DNA itself, which is less likely in a water-rich environment, and the other terms refer to different concepts (not the chemical process producing radicals).