What causes thymine dimers to form?

Thymine dimers are specific types of DNA damage that occur when two adjacent thymine bases in a DNA strand bond together due to exposure to ultraviolet (UV) light. This process involves the formation of covalent bonds between the carbon atoms of the two thymine bases, leading to a distortion in the DNA structure.

The critical aspect of this formation is the energy provided by UV light, which initiates the reaction that causes the two thymine molecules to covalently link. This can impede DNA replication and transcription, potentially leading to mutations if not repaired. The repair mechanism typically involves nucleotide excision repair, which recognizes the distortion and removes the dimer to allow for correct DNA synthesis.

The other options presented do not lead to the formation of thymine dimers in the same way. For instance, heat exposure may cause other forms of DNA damage, ionizing radiation can lead to different types of DNA lesions such as double-strand breaks, and replication errors typically refer to mistakes made during DNA synthesis rather than the specific covalent bonding between bases triggered by UV light.