DNA or deoxyribonucleic acid is the genetic material of humans and most other organisms. Almost all cells withinside the human frame have identical DNA. Most of the DNA is present in the nucleus (where it is called nuclear DNA), but a small amount is also present in the mitochondria (called mitochondrial DNA or mtDNA). Mitochondria are structures within cells that convert energy from food into a form that the cell can use. Information in DNA is stored as a code made up of four chemical radicals: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA is made up of about 3 billion bases and more than 99% of these bases are common to all people. The order or sequence of these bases determines the information that can be used to build and maintain an organism. This is much like how the letters of the alphabet appear in a particular order to form words and sentences. DNA bases are paired with A and T, C and G to form units called base pairs. Each base is also bound to a sugar molecule and a phosphate molecule. Bases, sugars, and phosphates together are called nucleotides. Nucleotides are organized in lengthy strands that shape a helix referred to as a double helix. The structure of the double helix resembles a ladder, with base pairs forming the steps of the ladder and sugar and phosphate molecules forming the vertical sides of the ladder. An important property of DNA is its ability to replicate or copy itself. Each DNA strand of the double helix acts as a template for replicating the base sequence. This is very important when cells are dividing.