What kind of mutation is usually caused by non-ionizing radiation (ultraviolet light)?
The correct answer and explanation is:
The mutation most commonly caused by non-ionizing radiation, such as ultraviolet (UV) light, is a point mutation that leads to thymine dimers. These are the result of UV light causing two adjacent thymine bases in DNA to bond inappropriately, forming a dimer. This distorts the DNA helix and can lead to errors during DNA replication if not repaired.
Thymine dimers are a type of pyrimidine dimer, which is a DNA lesion. UV radiation causes the formation of these dimers when the energy from UV light excites the electrons in the thymine bases, leading to covalent bonding between them. Normally, thymine bases pair with adenine in the DNA double helix. However, when UV radiation causes thymine dimers, the DNA structure is altered, and the cell’s repair mechanisms must intervene.
If these dimers are not properly repaired, they can result in mutations during DNA replication. Specifically, when DNA polymerase encounters the dimer during replication, it can either skip the dimer or insert the wrong base in place of the thymine bases. This can lead to substitution mutations, where one base is replaced by another, potentially causing changes in the protein coding sequence. In some cases, frameshift mutations can also occur if the repair mechanisms result in the deletion or insertion of bases.
In response to UV-induced damage, cells have repair mechanisms like nucleotide excision repair (NER), which can recognize and remove the dimers, allowing the DNA to be restored to its normal state. However, if the repair process fails or is overwhelmed by high levels of UV exposure, the mutations can accumulate, potentially leading to skin cancers like melanoma and basal cell carcinoma. The link between UV radiation and these cancers underscores the importance of protecting the skin from excessive UV exposure.