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[3] [4] Later, by characterizing the phenotypes of mutagenised E. coli, she and post doctoral student Miroslav Radman detailed the SOS response to UV radiation in bacteria. [3] [5] The SOS response to DNA damage was a seminal discovery because it was the first coordinated stress response to be elucidated. [6]
UV can also be used to remove chlorine and chloramine species from water; this process is called photolysis, and requires a higher dose than normal disinfection. The dead microorganisms are not removed from the water. UV disinfection does not remove dissolved organics, inorganic compounds or particles in the water. [102]
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.
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 ...
Photolyase is a phylogenetically old enzyme which is present and functional in many species, from the bacteria to the fungi to plants [9] and to the animals. [10] Photolyase is particularly important in repairing UV induced damage in plants.
UV exposure induces pili formation and cellular aggregation. [93] Cells with the ability to aggregate have greater survival than mutants lacking pili that are unable to aggregate. The frequency of recombination is increased by DNA damage induced by UV-irradiation [96] and by DNA damaging chemicals. [97]
These reactive chemical species can reach DNA by diffusion and the bimolecular reaction damages the DNA (oxidative stress). Unlike direct DNA damage which causes sunburn, indirect DNA damage does not result in any warning signal or pain in the human body. The bimolecular reactions that cause the indirect DNA damage are illustrated in the figure:
Bacterial bioluminescence has also been proposed to be a source of internal light in photoreactivation, a DNA repair process carried out by photolyase. [37] Experiments have shown that non-luminescent V. harveyi mutants are more sensitive to UV irradiation, suggesting the existence of a bioluminescent-mediated DNA repair system. [23]