Which UV type is known for causing photochemical damage to cellular DNA due to its energy?

• A. Infrared
• B. UVA
• C. UVB
• D. UVC

Answer: (C)

Different UV wavelengths carry different photon energies, which determines how they interact with DNA. Direct photochemical damage happens when DNA absorbs UV photons and the energy creates chemical changes, like thymine dimers. UVB, with wavelengths around 280–315 nm, has enough energy to be absorbed directly by DNA, producing these direct lesions. UVA has lower energy and tends to cause damage mainly through reactive oxygen species rather than direct DNA photochemistry. Infrared is not UV and doesn’t cause this kind of DNA photochemistry. UVC has even higher energy and can damage DNA directly as well, but it is largely blocked by the atmosphere and not a typical environmental exposure, making UVB the best match for photochemical DNA damage due to energy in common exposure contexts.