Your DNA damage looks great, did you get just get back from the beach?

My students in Biology 101 are learning about DNA right now and one asked me how UV radiation causes damage to our genetic material. I know the basics, but was unfamiliar with the process. So I, of course, was intrigued, and had to look it up. Bear with me, I’ve tried to make this as simple and bare-bones as possible, so don’t let your eyes glaze over (like those of some of my students) when you see big scientific words.
DNA structure consists of a backbone molecule made up of sugar (a deoxyribose sugar, what the D in it’s name stands for) paired with phosphate molecules. Attached to each of those sugars is a nitrogenous base: adenine (A), thymine (T), guanine (G) or cytosine (C). It’s the complimentary pairing nature of these bases that allows for such perfect replication of our genetic material; A pairs with T, and G pairs with C, and that is what gives DNA it’s structure, chemical properties, and it’s ability to replicate so faithfully.
DNA replicates, or copies itself, in a process that is nothing short of amazing. The double-helix structure unwinds (with the help of an enzyme) and each parent strand is faithfully copied via complimentary base pairing. Throughout the process are “checkpoints” to prevent errors and proofreaders that won’t allow the DNA to code for protein unless things are correct.
Most DNA damage interferes with the ability to proofread or prevent incorrect proteins from being made, which is the case with UV radiation. UVB light causes one of the nitrogenous bases, thymine, to pair with itself instead of with adenine. These thymine base pairs next to each other in genetic sequences bond together into thymine dimers, an incorrect sequence which disrupts replication in the strand and which enzymes cannot read or copy. This leads to the production of melanin--a tan, or in severe cases, sunburn. Sunburn is the body’s way to get rid of cells damaged by UV radiation.
Direct DNA damage is reduced by sunscreen, which prevents sunburn; it won’t necessarily keep you from getting a tan. On the skin’s surface, sunscreen filters the UV-rays, decreasing their intensity. When sunscreen molecules penetrate the skin, they protect against direct DNA damage because the UV-light is then absorbed by the sunscreen and not by DNA.
So, that beautiful golden color you get when you lay out in the sun, the one you think makes you look so good? Yeah, not so good. That damage accumulates in your DNA, and over time can lead to skin cancer.
We do need some sun, so I’m not advocating staying inside on beautiful afternoons, just be careful and use sunscreen to decrease your risks of skin cancer.