Thymine dimer

Thymine dimer is a molecular lesion, or damage, that can occur in DNA due to exposure to ultraviolet (UV) radiation. It involves the formation of a covalent bond between two adjacent thymine bases in a DNA strand. This can distort the DNA molecule, interfering with normal replication and transcription processes.

Formation

Thymine dimers are primarily formed when DNA absorbs UVB radiation, which has a wavelength of 280 to 315 nm. The energy from the radiation is absorbed by the DNA, causing a photochemical reaction that results in the formation of a cyclobutane ring between the two thymines. This is known as a Cyclobutane Pyrimidine Dimer (CPD).

Effects

The formation of a thymine dimer distorts the DNA helix, interfering with normal base pairing and causing errors during DNA replication. This can lead to mutations, which can cause cell death or lead to the development of skin cancer, particularly melanoma and non-melanoma skin cancer.

Repair

Cells have mechanisms to repair thymine dimers and other DNA damage. The primary repair mechanism for thymine dimers is nucleotide excision repair (NER), which involves the removal of the damaged section of DNA and its replacement with correct nucleotides. Another repair mechanism is photoreactivation, which uses an enzyme called photolyase to reverse the formation of the dimer.

See also

• DNA repair
• UVB radiation
• Skin cancer

References

Thymine dimer Resources
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