Indirect effect occurs when the initial ionizing event occurs on which type of molecule?

Indirect effect occurs when the initial ionizing event occurs on which type of molecule?

• A. DNA
• B. Water molecule
• C. Another molecule
• D. Lipids

Answer: (C)

Indirect effect happens because the radiation’s first ionization typically hits a molecule other than DNA, and in biological tissue that molecule is usually water. When water is ionized, it undergoes radiolysis and splits into highly reactive free radicals, especially the hydroxyl radical and solvated electrons. These reactive species diffuse through the cellular environment and subsequently attack DNA, causing strand breaks and base damage. Because water is so abundant in cells, most radiation-induced DNA damage from low-LET radiation stems from this indirect pathway. If the initial ionization occurred directly on DNA, you’d have a direct effect, but the dominant starting point is water molecule ionization leading to indirect damage.

Indirect effect happens because the radiation’s first ionization typically hits a molecule other than DNA, and in biological tissue that molecule is usually water. When water is ionized, it undergoes radiolysis and splits into highly reactive free radicals, especially the hydroxyl radical and solvated electrons. These reactive species diffuse through the cellular environment and subsequently attack DNA, causing strand breaks and base damage. Because water is so abundant in cells, most radiation-induced DNA damage from low-LET radiation stems from this indirect pathway. If the initial ionization occurred directly on DNA, you’d have a direct effect, but the dominant starting point is water molecule ionization leading to indirect damage.