I think the proactive stance is a better attitude to promote than after-the-fact worrying! When planning a long week of sunbathing on the beach, What type of DNA damage should sunbathers be aware of before hitting the beach?

Question

A.  photolyase-induced mutations
B.  decreased telomere length
C.  thymine dimers
D.  activation of uvr A, B, and C genes

Clarify Question
· What is the key concept addressed by the question?
  · What type of thinking is required?
  · What key words does the question contain?
 
Gather Content
· What do you already know about light-induced DNA damage?
 
Consider Possibilities
· Consider the different answer options. Which can you rule out?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
  Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  thymine dimers

Clarify Question
· What is the key concept addressed by the question?
    o This question addresses light-induced DNA damage.
  · What type of thinking is required?
    o Although you may not have seen this example before, you know enough about the concept to Apply your knowledge and understanding to this unfamiliar situation.
  · What key words does the question contain?
    o DNA damage refers to a defect in the structure of DNA, often caused by chemicals (mutagens) or UV light.
 
Gather Content
· What do you already know about light-induced DNA damage?
    o Sunlight includes UV radiation which can be damaging to DNA.
    o UV light damages DNA by causing formation of thymine dimers.
    o When two thymines are adjacent, they can become bound together, distorting the helix of the DNA. This can lead to a permanent mutation after DNA replication.
 
Consider Possibilities
· Consider the different answer options. Which can you rule out?
    o Two of the answer options refer not to DNA damage, but to DNA repair mechanisms: photolyase and the uvr genes act to repair DNA. We are looking for an example of UV-light induced DNA damage.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
    o Decreased telomere length would be damaging to DNA, but this is not a common result from UV-light.
    o Instead, formation of thymine dimers is the most common photoproduct of DNA damage.
    o It activates the photorepair pathway, involving recognition of the thymine dimer by photolyase. (So, photolyase is a “good guy”!)
  Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
    o This question required you to Apply your knowledge and understanding to this unfamiliar situation.
    o Did you remember that thymine dimers are a common result of DNA damage?     o Did you recognize that photolyase and the uvr genes help repair DNA?
    o Next time you plan a day in the sun, how can you reduce your risk of thymine dimer formation?