Direct effect occurs when radiation energy is deposited directly to which molecule?

Direct effect occurs when radiation energy is deposited directly to which molecule?

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

Answer: (A)

Direct effects happen when the radiation energy is deposited directly in a biomolecule, causing ionizations and breakage of its bonds. In cells, DNA is the critical target because damage to its structure—such as strand breaks, base damage, and cross-links—directly impairs replication and cell viability. While the abundant water in cells largely undergoes radiolysis to produce free radicals that cause indirect damage to DNA and other molecules, the direct effect specifically refers to energy deposited in DNA itself. Proteins and lipids can also be damaged, but the most characteristic direct interaction is with DNA.

Direct effects happen when the radiation energy is deposited directly in a biomolecule, causing ionizations and breakage of its bonds. In cells, DNA is the critical target because damage to its structure—such as strand breaks, base damage, and cross-links—directly impairs replication and cell viability. While the abundant water in cells largely undergoes radiolysis to produce free radicals that cause indirect damage to DNA and other molecules, the direct effect specifically refers to energy deposited in DNA itself. Proteins and lipids can also be damaged, but the most characteristic direct interaction is with DNA.