DNA and Double-Stranded Oligonucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 346

Fig. 12.1a-i Schematic representation of some types of DNA damage in dsDNA caused by ionizing
radiation: a base damage; b AP site; c SSB; d DSB from two close-by SSBs; e tandem lesion; f clus-
tered lesion with two damaged bases at opposite strands; g SSB with damaged base on opposite
strand; h clustered lesion with three damaged bases; i clustered lesion with a DSB (from two close-
by SSBs) and two damaged bases. Upon enzymatic treatment, a, b and e may turn into a SSB, while f
and g may give rise to a DSB. The complex lesion h may not be recognized by the enzyme at all, nor
would an enzyme treatment of i be detectable, since it already contains a DSB

Table 12 .1. Some of the damage in a mammalian cell nucleus from 1 Gy of low-LET radia-
tion. (Ward 1988; Goodhead 1994)

Initial physical damage

Ionizations in the cell nucleus

∼ 100,000

Ionizations directly in DNA ∼ 2000

Excitations directly in DNA ∼ 2000

Selected biochemical damage

SSBs 1000

8-oxo-A (a typical single-base damage) 700

DSBs 40

DNA − protein cross-links 150

Selected cellular effects

Lethal events ∼ 0.2-0.8

Chromosome aberrations ∼ 1

∼ 10 -5

Hprt mutations