Photolyase

Definition

Photolyase is an enzyme that plays a crucial role in the DNA repair process by specifically recognizing and repairing UV-induced damage, particularly pyrimidine dimers. This enzyme uses the energy from light to catalyze the cleavage of these dimers, thereby restoring the DNA to its normal structure and function. Photolyase is a key player in the cellular mechanisms that maintain genetic stability by preventing mutations caused by environmental factors such as UV radiation.

5 Must Know Facts For Your Next Test

1. Photolyase is found in many organisms, including bacteria, plants, and some animals, but is absent in mammals.
2. The enzyme requires a chromophore, such as FADH\2, to absorb light energy, which is then used to repair damaged DNA.
3. Photolyase can repair DNA damage in a light-dependent manner, meaning it is most effective when exposed to UV or blue light.
4. There are two types of photolyase: one that repairs cyclobutane pyrimidine dimers and another that repairs (6-4) photoproducts.
5. The action of photolyase helps prevent mutations that could lead to diseases such as skin cancer in organisms exposed to UV radiation.

Review Questions

• How does photolyase specifically target and repair UV-induced DNA damage?
  • Photolyase targets UV-induced DNA damage by recognizing pyrimidine dimers formed from adjacent thymine or cytosine bases. Once the enzyme binds to the damaged site, it absorbs light energy, which enables it to cleave the bonds between the dimerized bases. This repair process restores the normal structure of the DNA, effectively reversing the mutation that could have been caused by UV exposure.
• Compare and contrast photolyase with nucleotide excision repair in terms of their mechanisms for repairing DNA damage.
  • Photolyase and nucleotide excision repair are both vital for maintaining DNA integrity but differ in their mechanisms. Photolyase directly repairs specific UV-induced lesions by using light energy to break apart pyrimidine dimers. In contrast, nucleotide excision repair involves a more complex process where damaged nucleotides are recognized and removed from the DNA strand, followed by synthesis of new nucleotides to fill in the gaps. While photolyase operates primarily in response to UV damage, nucleotide excision repair addresses a broader range of lesions.
• Evaluate the significance of photolyase in protecting organisms from UV-induced mutations and its implications for cancer prevention.
  • The significance of photolyase lies in its ability to directly reverse UV-induced DNA damage, thus playing a crucial role in preventing mutations that can lead to cancer. By efficiently repairing pyrimidine dimers before they can cause replication errors during cell division, photolyase helps maintain genetic stability. This function is particularly important for organisms frequently exposed to sunlight, as it reduces the risk of developing skin cancers and other UV-related diseases. Understanding how photolyase works could lead to advances in cancer therapies or protective strategies against UV exposure.

Related terms

Pyrimidine dimers: DNA lesions formed when two adjacent thymine or cytosine bases bond together due to UV light exposure, leading to distortions in the DNA structure.

Nucleotide excision repair: A DNA repair mechanism that removes damaged nucleotides and replaces them with the correct ones, often used for various types of DNA damage, including bulky adducts.

Cryptochrome: A protein related to photolyase that also absorbs light and plays roles in circadian rhythms and plant growth, though it does not have DNA repair functions.