Radiation causes the bonds between atoms to break. This can create ions, which is why the term ionizing radiation is often used in this context. As bonds are broken, large complex molecules like proteins and DNA are damaged, which can have negative impacts on the cell's ability to function. Also, as molecules break, smaller molecules and ions (sometimes called free radicals) normally not found in the cell are produced, and they can create a variety of problems. Free radicals are quite chemically active, and can disrupt the bonds holding other nearby molecules together; for this reason, the effects of radiation may continue long after the actual radiation has stopped.
Far and away the biggest impact of radiation on cells is in the disruption of DNA. When DNA is disrupted, the cell loses the ability to create proteins needed for metabolism, and also loses the ability to repair itself. If the damaged DNA is passed on to daughter cells by mitosis or meiosis, you can end up with a whole group of cells that no longer function correctly.
Injury to living tissue results from the transfer of energy to atoms and molecules in the cellular structure. Ionizing radiation causes atoms and molecules to become ionized or excited. These excitations and ionizations can:
- Produce free radicals.
- Break chemical bonds.
- Produce new chemical bonds and cross-linkage between macromolecules.
- Damage molecules that regulate vital cell processes (e.g. DNA, RNA, proteins).
The cell can repair certain levels of cell damage. At low doses, such as that received every day from background radiation, cellular damage is rapidly repaired.
At higher levels, cell death results. At extremely high doses, cells cannot be replaced quickly enough, and tissues fail to function.
Prompt and Delayed Effects
Radiation effects can be categorized by when they appear.
- Prompt effects: effects, including radiation sickness and radiation burns, seen immediately after large doses of radiation delivered over short periods of time.
- Delayed effects: effects such as cataract formation and cancer induction that may appear months or years after a radiation exposure