<unk>  can occur when<unk> <unk> ly absorbs a UVB photon, or for numerous other reasons. UVB light causes thymine base pairs next to each other in genetic sequences to bond together into pyrimidine dimers, a disruption in the strand, which reproductive enzymes cannot copy. It causes sunburn and it triggers the production of melanin. Other names for the<unk> " are: *thymine dimers *pyrimidine dimers *Cyclobutane Pyrimidine Dimers (CPDs) *UV-endonuclease-sensitive-sites (ESS) Due to the excellent photochemical properties of<unk> , this nature-made molecule is damaged by only a tiny fraction of the absorbed photons.<unk>  transforms more than 99.9% of the photons into harmless heat (but the damage from the remaining < 0.1% is still enough to cause sunburn). The transformation of excitation energy into harmless heat occurs via a photochemical process called internal conversion. In<unk> , this internal conversion is extremely fast, and therefore efficient. This ultrafast (subpicosecond) internal conversion is a powerful photoprotection provided by single nucleotides. However, the Ground-State Recovery is much slower (picoseconds) in G·C−DNA duplexes and hairpins. It is presumed to be even slower for double-stranded<unk>  in conditions of the nucleus. The absorption spectrum of<unk>  shows a strong absorption for UVB radiation and a much lower absorption for UVA radiation. Since the action spectrum of sunburn is indistinguishable from the absorption spectrum of<unk> , it is generally accepted that the<unk> s are the cause of sunburn. While the human body reacts to<unk> s with a painful warning signal, no such warning signal is generated from indirect<unk>  damage.
Direct DNA damage
Indirect DNA damage
DNA replication stress
DNA condensation
DNA fragmentation
Viral interference
DNA laddering
DNA adduct