The Effects of Radiation on DNA Mutations

Radiation, or more specifically, X and gamma “ionizing” radiation can wreak havoc on the molecules of your DNA—the genetic blueprint of your body. A strong dose of radiation can kill cells, the effect of which can be immediately apparent. Non-lethal doses are another matter. According to the Department of Energy’s (DOE) website, “The effect of the radiation may not be to kill the cell, but to alter its DNA code in a way that leaves the cell alive but with an error in the DNA blueprint.” This “error” is known as a mutation.

Mutation and DNA

• According to the DOE, “DNA molecules are enormously long chains of atoms wound around proteins and packed into structures called chromosomes within the cell nucleus.” Ionizing radiation pushes the electron out of its orbit around the nucleus of an atom. If this electron is from a DNA or neighboring molecule and “directly strikes and disrupts the DNA molecule,” the effect is known as direct action. Indirect action, the process responsible for most DNA damage caused by x-rays, occurs when the displaced electron ionizes a water molecule, creating a free radical. As the free radical drifts, trying to restore “a stable configuration of electrons,” it may disrupt a DNA molecule. Whether the action is direct or indirect, if it damages a DNA molecule, a mutation may occur.

  Radiation’s effect on neutrons, however, can cause a neutron to directly strike an atomic nucleus--usually carbon or oxygen nuclei--knocking out fragments of the nucleus. These particles then ionize nearby electrons, creating the free radicalization process described above.

Somatic Cells

• When radiation creates mutation in non-germ cells, it can eventually lead to loss of the affected cell’s ability to control its division. Though the effect may not appear for a number of years, the eventual, uninhibited cell division may cause cancerous growth. Because cancers due to radiation exposure are no different than other cancers, science has no way of figuring the rate of radiation-caused cancer. However, the DOE points out that certain parts of the body are more “radiosensitive” than others. “For example, bone marrow is more sensitive than skin cells to radiation-induced cancer,” says the DOE.

Germ Cells

• Mutations caused in germ cells—sperm and ova—are called “genetic or inheritable” effects. The DOE makes it clear that radiation-caused mutation does not result in the “visual monstrosities of science fiction.” Rather, the mutation produces a “greater frequency” of the types of mutations--positive and negative--that occur naturally through evolution. Research in this area is limited to animal studies and studies of Japanese survivors of the atomic bombs dropped on Hiroshima and Nagasaki. There is debate among researchers over the extent and consequences to humans from radiation-induced, inheritable mutation. Studies have shown great differences between species of animals in their susceptibility to genetic mutation. For example, fruit flies’ large chromosomes seem to be particularly sensitive to genetic mutation, while humans “may be less vulnerable than previously thought,” according to the DOE.