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DNA is short for deoxyribonucleic (dee-ox-ee-rye-bo-new-clay-ick) acid. (Try saying that 3 times real fast!) It is the genetic blueprint, or recipe, for making all living things. Almost every cell in your body contains DNA and all the information needed to make you what you are, from the way you look to which hand you write with.
DNA is shaped like a long ladder that's twisted into a spiral. If all the DNA in just one of your cells was unpacked and stretched out straight, it would be two yards long. Since you have about five trillion (5,000,000,000,000) cells in your body, the total length of DNA packed into you would stretch from here to the sun and back 30 times!
DNA is wound and coiled into structures called chromosomes (crow-mo-somes). In animals, plants, fungi and protists, these chromosomes are enclosed in a compartment within their cells called a nucleus (new-klee-us). In bacteria and archaea, the chromosome is not enclosed in a nucleus and floats free in their cytoplasm (sigh-toe-plazm), the fluid inside cells.
The sides of the DNA ladder are long chains of sugars and phosphates (fahs-fates). The rungs of the ladder are four chemical bases: adenine (add-n-een), guanine (gwa-neen), cytosine (sigh-tuh-seen) and thymine (thigh-meen). Adenine (A) always pairs with thymine (T) and guanine (G) always pairs with cytosine (C).
It's the sequence of these bases that makes up the genetic code or blueprint that determines all of the traits of living things. It may be hard to believe at first—how can things as different as grasshoppers and elephants be built from the arrangement of just four chemical bases?
The genetic code is like a musical score. In music, the instructions for all songs and tunes are created from just eight different notes. These eight notes have been arranged and rearranged in a wide variety of combinations to create the scores for every piece of music ever produced, from a Beethoven symphony to a Beastie Boys rap.
Similarly, the four chemical bases of DNA have been arranged and rearranged in numerous combinations to create the scores, or genomes (gee-nomes), of almost every creature that has ever lived.
Some viruses don't have DNA. Instead, their genetic blueprint is RNA, or ribonucleic (rye-boh-new-clay-ick) acid.
RNA looks like one half of the DNA ladder. It has a single long chain of sugars and phosphates and four chemical bases, though not in pairs. Instead of thymine, RNA has uracil (your-uh-sill) (U).
When RNA viruses infect cells, they first have to use the host cell's machinery to turn their RNA into DNA before they can begin reproducing.