DNA molecules are extremely large (the molecular weight is generally at least one million), and the main components are adenine deoxynucleotides, guanine deoxynucleotides, cytosine deoxynucleotides and thymine deoxynucleotides. DNA exists in the nucleus, mitochondria and chloroplasts, and can also exist in the cytoplasm of some cells in a free state. Most known phages, some animal viruses and a few plant viruses also contain DNA.
Except RNA and phage, DNA is the genetic material basis of all living things. The similarity and inheritance between parents and children of living things, that is, the so-called genetic information, are all stored in DNA molecules. 1953, james watson and francis crick described the structure of DNA: a pair of polynucleotide chains are intertwined to form a double helix. Therefore, they shared/kloc-with Frederic Wilkins, a physicist at National Institute of Technology in London.