Thymine Cyclobutane Dimer (TCD) is a specific type of DNA damage that occurs when two adjacent thymine nucleotides on the same DNA strand covalently bond together, forming a cyclobutane ring. TCD is primarily induced by exposure to ultraviolet (UV) radiation, particularly in the shorter wavelength range of UVB.
This type of DNA damage is significant as it can disrupt the normal structure and function of DNA molecules. TCDs cause bending or kinking of the DNA double helix, leading to structural distortions. These distortions can impede DNA replication, transcription, and DNA repair processes.
The formation of TCDs is a result of a photochemical reaction triggered by UV radiation. When two adjacent thymine bases absorb UV energy, the photons cause a rearrangement of chemical bonds within the DNA molecule, resulting in the formation of a four-membered cyclobutane ring. This covalent bond formation between the two thymines creates a dimer, which interrupts the normal hydrogen bonding patterns in DNA strands.
If left unrepaired, TCDs can lead to genetic mutations, which can have detrimental effects on an organism's health. However, cells have evolved various repair mechanisms to correct TCDs, such as nucleotide excision repair (NER) that removes and replaces the damaged DNA segments.
In summary, a thymine cyclobutane dimer refers to a specific form of DNA damage caused by UV radiation, where two adjacent thymine nucleotides form a covalent cyclobutane ring.
