Search results
Results from the WOW.Com Content Network
Indirect DNA damage occurs when a UV-photon is absorbed in the human skin by a chromophore that does not have the ability to convert the energy into harmless heat very quickly. [2] Molecules that do not have this ability have a long-lived excited state .
Nucleotide excision repair (NER) is a particularly important excision mechanism that removes DNA damage induced by ultraviolet light (UV). UV DNA damage results in bulky DNA adducts — these adducts are mostly thymine dimers and 6,4-photoproducts. Recognition of the damage leads to removal of a short single-stranded DNA segment that contains ...
In human cells, oxidative DNA damage occurs about 10,000 times a day and DNA double-strand breaks occur about 10 to 50 times a cell cycle in somatic replicating cells (see DNA damage (naturally occurring)). The selective advantage of DNA repair is to allow the cell to survive in the face of DNA damage.
Melanoma cells are commonly defective in postreplication repair of DNA damages that are in the form of cyclobutane pyrimidine dimers, a type of damage caused by ultraviolet radiation. [ 11 ] [ 12 ] A particular repair process that appears to be defective in melanoma cells is homologous recombinational repair. [ 12 ]
This process of absorption works to reduce the risk of DNA damage and the formation of pyrimidine dimers. UVA light makes up 95% of the UV light that reaches earth, whereas UVB light makes up only about 5%. UVB light is the form of UV light that is responsible for tanning and burning. Sunscreens work to protect from both UVA and UVB rays.
Photolyase is particularly important in repairing UV induced damage in plants. The photolyase mechanism is no longer working in humans and other placental mammals who instead rely on the less efficient nucleotide excision repair mechanism , although they do retain many cryptochromes . [ 11 ]
The AP endonucleases also participate in 3' end processing. Besides opening AP sites, they possess 3' phosphodiesterase activity and can remove a variety of 3' lesions including phosphates, phosphoglycolates, and aldehydes. 3'-Processing must occur before DNA synthesis can initiate because DNA polymerases require a 3' hydroxyl to extend from.
The system can also inhibit cell division and cell respiration. [1] The SOS response has been proposed as a model for bacterial evolution of certain types of antibiotic resistance. [2] The SOS response is a global response to DNA damage in which the cell cycle is arrested and DNA repair and mutagenesis are induced.