The much more energetic gamma rays and X rays, like ultraviolet rays, can interact directly with the DNA molecule. However, they cause most of their damage by ionizing the molecules, especially water, surrounding the DNA. This forms free radicals, chemical substances with an unpaired electron. These free radicals, especially those containing oxygen, are extremely reactive, and they immediately attack neighboring molecules. When such a free radical attacks a DNA molecule, it can change a base, but it frequently causes a single- or double-stranded break. Single-stranded breaks are ordinarily not serious because they are easily repaired, just by rejoining the ends of the severed strand, but double-stranded breaks are very difficult to repair properly, so they frequently cause a lasting mutation. Because ionizing radiation can break chromosomes, it is referred to not only as a mutagen, or mutation-causing substance, but also as a clastogen, which means "breaker."
feedback form |
permissions |
international |
locate your campus rep |
request a review copy
Copyright ©2001 The McGraw-Hill Companies.
digital solutions |
publish with us |
customer service |
mhhe home
Any use is subject to the
Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of the
The McGraw-Hill Companies.