Question

What is the difference between direct and indirect action of radiation on DNA?

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Answer 1

Direct ionization occurs when charged particles such as electrons or alpha particles with appropriate kinetic energy reacts with atoms and molecules to liberate electrons and also create free radicals. This process is known as direct due to the fact that no intermediary step is required here.

Indirect ionization occurs when non-charged particles such as photons and neutrons interact with atoms and molecules. The term indirect means that the uncharged particles themselves are not creating the free radicals which results in biological damage to the cell and it also requires the intermediate step for the creation of charged particles.

Direct and indirect action of radiation on the DNA molecules results in damage to the cell. In direct action, the radiation hits the DNA molecule directly and thus disturbing the molecular structure of DNA. This type of structural change leads to cell damage or even cell death. Damaged cells that survive may later induce carcinogenesis or other abnormalities.

In the indirect action, the radiation hits the water molecules and other organic molecules present in the cell and produce free radicals ( unpaired electron or highly reactive species) such as hydroxyl (HO•) etc in the cell.