DNA repair: Dynamic defenders against cancer and aging Page: 2 of 16
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You probably weren't thinking about your body's cellular DNA repair systems the last time you
sat on the beach in the bright sunshine. Fortunately, however, while you were subjecting your
DNA to the harmful effects of ultraviolet light, your cells were busy repairing the damage. The
idea that our genetic material could be damaged by the sun was not appreciated in the early
days of molecular biology. When Watson and Crick discovered the structure of DNA in 1953 ,
it was assumed that DNA is fundamentally stable since it carries the blueprint of life. However,
over 50 years of research have revealed that our DNA is under constant assault by sunlight,
oxygen, radiation, various chemicals, and even our own cellular processes. Cleverly, evolution
has provided our cells with a diverse set of tools to repair the damage that Mother Nature
DNA repair processes restore the normal nucleotide sequence and DNA structure of the
genome after damage . These responses are highly varied and exquisitely regulated. DNA
repair mechanisms are traditionally characterized by the type of damage repaired. A large
variety of chemical modifications can alter normal DNA bases and either lead to mutations or
block transcription if not repaired, and three distinct pathways exist to remove base damage.
Base excision repair (BER) corrects DNA base alterations that do not distort the overall
structure of the DNA helix such as bases damaged by oxidation resulting from normal cellular
metabolism. While BER removes single damaged bases, nucleotide excision repair (NER)
removes short segments of nucleotides (called oligonucleotides) containing damaged bases.
NER responds to any alteration that distorts the DNA helix and is the mechanism responsible
for repairing bulky base damage caused by carcinogenic chemicals such as benzo [a]pyrene
(found in cigarette smoke and automobile exhaust) as well as covalent linkages between
adjacent pyrimidine bases resulting from the ultraviolet (UV) component of sunlight. NER can be
divided into two classes based on where the repair occurs. NER occurring in DNA that is not
undergoing transcription (i.e., most of the genome) is called global genome repair (GGR or GG-
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Fuss, Jill O. & Cooper, Priscilla K. DNA repair: Dynamic defenders against cancer and aging, article, April 1, 2006; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc884361/m1/2/: accessed November 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.