Ionizing Radiation is very, very bad for DNA. There are two ways this radiation can alter DNA:
- Direct: Ionizing radiation can induce covalent linkages between nitrogenous bases, creating structures like thymine dimers.
- Indirect: Ionizing radiation can interact with water to create free radicals, which can interact with DNA and cause single or double-stranded breaks in the sugar-phosphate backbone.
A measure of the dose of radiation absorbed by an organism is the rad, which is defined as 1 erg/gram. 100 rads = 1 Grey (Gy) which is the normally used unit for radiation exposure.
It is interesting to note that bacteria have a much higher tolerance for radiation than most eukaryotes. For instance, 10 Greys is considered a lethal dose for humans; 200 Greys will barely decrease viability of Salmonella spp. by 10%. On the extreme end of the scale, 2,200 Greys will barely decrease Deinococcus radiodurans viability by 10%.