Answer:
The impact of radiation on living tissue is complicated by the type of radiation and the variety of tissues but let´s try to understand how it would affect DNA.
Ionizing radiation, by definition, "ionizes" that means that it can remove electrons from an atom. When ionizing radiation interacts with a cell, several things can happen:
1) The radiation could pass through the cell without damaging the DNA
2) It could damage cell´s DNA but the DNA repairs itself
3)It could prevent the DNA from replicating
4) It could damage the DNA so badly that the cell dies. This is called apoptosis.
Alpha particles, beta particles and X-rays can directly affect a DNA molecule in different ways:
-Changing the chemical structure of bases
-Breaking the sugar-phosphate backbone
-Breaking the hydrogen bonds conncecting the base pairs
Direct action can lead to either DNA damage or DNA mutations (changes to the sequence of base pairs that are not repaired).
Radiation can also interact indirectly with DNA: it can affect other molecules creating free radicals (hydrogen (H+) and hydroxyls (OH-) ions). Free radicals are highly reactive, they can react with hydrogen atoms inside a DNA molecule to form hydrogen peroxide (H2O2). This can cause the types of DNA damage we talked about earlier.