|MadSci Network: Genetics|
Hello! In order to answer your question, let's start with what DNA looks like. DNA is a molecule that resembles a long string with differently shaped tabs attached along the length of it. There are four shapes to these tabs, called adenosine, guanine, cytosine and thymine. The proper name for these four tabs is "bases". Think of the order of bases along the DNA string as the words to the instruction manual for the cell. A molecule (called RNA polymerase) rolls along the DNA and reads the bases, then makes a copy which gets sent out to the rest of the cell. Ultraviolet light damages DNA by changing the shape of the thymine base. If two thymines are attached side by side along the DNA molecule, ultraviolet light will stick the two bases together and warp the DNA strand. This makes it impossible for the RNA polymerase to read the instructions so it makes a bad copy that gets sent out to the cell, and as a result, the cell acts abnormally, or it may even die. There are repair systems in every cell to fix damaged DNA, but it can get overpowered if there is too much damage. Any cell can have its DNA damaged by ultraviolet light, be it from your heart, your liver or your lungs. Fortunately for us, the skin absorbs ultraviolet light and so protects our inside organs. Aside from the skin, our eyes and hair get damaged by ultraviolet light. It isn't the damage to the DNA that is important with our eyes and hair- in this case, the ultraviolet light creates very energetic molecules called free radicals which destroy the proteins in the lens of your eye (where you see out from), and in your hair, which is why you get streaks in your hair from being out in the sun. All in all, enjoy going out in the sun, but keep in mind the ultraviolet light and dress appropriately! Evelyne here are my references: 1. Molecular Cell Biology. 2nd ed. 1990. J. Darnell, H. Lodish, and D. Baltimore. pub: Scientific American Books, Inc., New York. 2. Solar Protection. 1998. R. Souccar. pub: Actualité Santé, Paris.
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