Contrast the various types of DNA repair mechanisms known to counteract the effects of UV radiation. What is the role of visible light in repairing UV-induced mutations?

Key Concepts

DNA Repair Mechanisms

DNA repair mechanisms are cellular processes that identify and correct damage to the DNA molecules that encode an organism's genome. These mechanisms are crucial for maintaining genetic stability and preventing mutations. Key types include nucleotide excision repair, which removes bulky DNA adducts, and photoreactivation, which directly reverses UV-induced damage.

Nucleotide Excision Repair (NER)

Nucleotide excision repair (NER) is a DNA repair mechanism that removes a wide range of DNA lesions, including those caused by UV radiation. In NER, damaged DNA is excised and replaced with the correct nucleotides, restoring the original sequence. This process is essential for preventing mutations that can lead to skin cancer and other diseases associated with UV exposure.

Photoreactivation

Photoreactivation is a light-dependent DNA repair process that specifically targets UV-induced pyrimidine dimers, which are covalent linkages between adjacent thymine or cytosine bases. This mechanism involves the enzyme photolyase, which, upon absorbing visible light, catalyzes the cleavage of these dimers, effectively reversing the damage without the need for excision and resynthesis.