Every year Sarah & I go to Mexico Beach, FL (it’s on the pan-handle, a little too close to Panama City Beach) with a select group of our undergraduate friends, and mountains of work will not stop us from attending this year.
What better way to prepare for our beach vacay than to remind ourselves of why we put on sunscreen? Also, I want to go over why it’s better to tan outside rather than inside a tanning bed. I remember being told that tanning beds were evil, and that the sun wasn’t nearly as bad - we’re usually told things when we’re younger that we just believe, but this actually has very interesting science behind it!
UV radiation & DNA
UV-B radiation (280-320nm) in sunlight & tanning lights can cause distortions in the DNA double helix that interfere with proper replication and transcription. Exposure to UV light causes adjacent cytosine (C) and thymine (T) bases to cross-link (pic right, down, via). This cross-link forms a pyrimidine dimer and disrupts the normal base pairing and creates a “bulge” in the DNA (pic left, via). Because these dimers cannot effectively base pair with other nucleotides they can cause DNA polymerase (needed for replication & transcription) to slow down or completely stop – stalling cellular life. “Any living tissue, even one in which cell division does not occur, has to be able to either avoid or repair UV-induced damage if it is to survive”.
DNA repair systems
After the initial break of the DNA, exonucleases excise the pyrimidine dimer (pic below, via). The action of cutting out damaged DNA happens frequently in DNA damage and is quickly repaired by DNA polymerase, which fills in the gap by synthesizing new DNA - using the bottom, intact strand as a template. After this, DNA ligase seals the remaining gap and joins old and new DNA.
Memorial Break Vacay Lesson #2: Don’t go to tanning beds. Aside from the above point, there’s nothing more unattractive than an over-tanned raisin.