What Is DNA?
DNA is present in the cells of every life form, whether it is a bacterium or
Hi, I'm Jim Shields for About.com, and today I'm going to teach you about DNA. When a baby is conceived in its mother's womb, it starts as the union of a male sperm cell and a female egg cell. The fertilized egg began growing into a fetus, which, in turn, is born as you and you just continued to grow. These initial two cells, the sperm and egg, continue to replicate, which we call "growth." But how does each cell know what to become? Why do some cells know to become eye cells and others ear cells, and still others hair cells? The key is DNA.DNA, which is short for deoxyribonucleic acid, is like an instruction manual contained within every cell in your body. Each cell in our bodies has the instructions for every cell. The DNA particle is formed in strands made up of four different molecules. Each strand is entwined in a pair called a "double helix" which looks kind of like a long sprial staircase.And it has a unique arrangement of these four molecules: guanine, adenine, thymine and cytosine. This unique arrangement of the 4 molecules determines what instructions the DNA will give to the cell about what to kind of cell to become and about what kinds of proteins to produce to help it work with other cells. DNA is present in the cells of every life form, whether it is a bacterium, a plant or a mammal. It might surprise you to know that if we were to remove a coiled strand of DNA from one of your cells and stretch it to its full length, it would be over 6 feet long. But when coiled within the cell, it is less than a tenth of a millimeter. Thanks for watching. To learn more about biology, visit us on the web at About.com.