What is DNA?
DNA (deoxyribonucleic acid) is the hereditary material in almost all organisms. In 1953 the structure of the DNA was enlightened for the first time by the researchers J. Watson and F. Crick. They proposed that DNA consists of two long strands that are built up chain-like. There are four chain links (nucleotides), each consisting of three subunits: a sugar (desoxyribose), a phosphate group and a chemical base (adenine, guanine, cytosine or thymine). The nucleotides only differ in the base from each other and are arranged pairwise in the middle of the DNA. Adenine (A) only binds to thymine (T) and cytosine (C) only to guanine (G). Due to the specific matching of the bases, it is sufficient to list the initial letter of particular bases for stating the chromosomes sequence.
The structure of the DNA is comparable to a ladder, with the sugar and phosphate molecules forming the vertical sidepieces and the base pairs forming the rungs. The DNA is screwed in that way, that it forms a spiral called double helix. The order (sequence) of the bases is in particular interesting for researchers, because they determine the biological information available for building and maintaining an organism.
An important property of the DNA is that it can replicate. This means that each strand of DNA double helix can serve as a pattern for making an exact copy of the sequence of bases, which is critical for cell division.
In eukaryotes (animals with a nucleus in their cells), most DNA is located in the cell nucleus. But a small amount of DNA can also be found in the mitochondria (mtDNA).
Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are alike in all humans. The total length of DNA in a single somatic cell is approximately two meters. This is amazing when you think about the small size of one cell. If you make a point on the surface of your hand with a pen, you mark about 1.000 cells. The human body consists of more than 50 trillion cells and thus of more than 100 billion kilometers of DNA!
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