Ionizing radiation breaks

Chromosome aberrations. Ionizing radiations break chromosomes presumably through DNA double-strand breakage (2, 3) and are capable of inducing aberrations in all phases of the cell cycle. 3AB potentiates the induction of chromosome aberrations by sparsely ionizing radiations, such as X- and y-rays (4-7), but does not affect the yields induced by densely ionizing fast neutrons (4). This indicates that poly(ADP-ribose) plays a different role in response to these types of radiation. 

Doublestrand break repair Ionizing radiation, chemotherapy, oxidative free radicals Synapsis, unwinding, alignment, ligation... 

Growing tissues are most sensitive to ionizing radiation. DNA synthesis is inhibited, yet the action of x-rays is indirect. They produce free radicals, which in turn react with DNA and thus produce point mutations or chromosomal breaks. 

Ion pairs created by ionizing radiation eventually produce free radicals that disrupt the biochemistry of cells, break chemical bonds, and otherwise produce cell damage. Free radicals are highly reactive atoms that scavenge electrons from other atoms or molecules, causing a chain reaction that can produce cell and tissue damage. 

Several studies have reported the influence of nitroimidazole derivatives on biological systems. Thus the influence of Misonidazole, l-(2-nitro-l-imidazoyl)-3-methoxy-propan-2-ol, on strand breaking in calf thymus DNA under ionizing radiation conditions has been assessed70. Pulse-radiolysis studies of nitroheterocyclic compounds have examined... 

The formation of J/-H2A.X occurs rapidly after the production of double strand breaks by ionizing radiation with detectable amounts present in seconds and maximal levels reached in about 10 min [57]. y-H2A.X disappears with kinetics consistent with the repair of the double stranded break. Western blots with antibodies that specifically recognize the phosphorylated SQ motif indicate that phosphorylation of this motif occurs in response to double breaks in many organisms, including Drosophila and S. cerevisiae [58]. 

Boubnov NV, Hall KT, Wills Z, et al. Complementation of the ionizing radiation sensitivity, DNA end binding, and V(D)J recombination defects of double-strand break repair mutants by the p86 Ku autoantigen. Proc Natl Acad Sci USA 1995 92(3) 890-894. 

Ionizing radiation, such as gamma rays and x-rays, causes complex types of DNA damage that are difficult to repair. Including double-strand and single-strand breaks and cross-links that may lead to leukemia and cancers of many organs. 

Injury to cell plasma membrane can activate acid sphingomyelinase to break down membrane lipid sphingomyelin and generate the second messenger ceramide, a complex lipid, to initiate the apoptosis (HI). Ceramide, perhaps through intracellular mitogen-activated protein kinases (MAPK), can alter cellular susceptibility to TNF-a, FasL, and ionizing radiation-induced apoptosis (HI, Wll). 

The primary target of biological effects appears to be the DNA (see Chap. 15), although effect on the cytoplasmic membrane may also play a role [8]. Ionizing radiation affects DNA in a number of ways. It causes chemical changes in specific nucleotide bases it causes single-strand breaks and it causes double-strand breaks in a dose-dependent manner. 

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