DNA stand for deoxyribonucleic acid. DNA is the hereditary material in humans and almost ever other living organism. DNA can be found in the nucleus of cells and in the mitochondria. Most of the DNA is in the nucleus and is called nuclear DNA. A small amount of DNA is in the mitochondria and is called mitochondrial DNA.
One of DNA’s most important properties is its ability to make copies of itself, or replicate. Each strand of DNA serves as the pattern for duplicating its sequence. When cells divide, this replication is important because new cells need to have an exact copy of the DNA from the old cell.
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.