The discovery that DNA was the carrier of genetic information was a process that required many earlier discoveries. The existence of DNA was discovered in the mid 19th century. However, it was only in the early 20th century that researchers began suggesting that it might store genetic information. This gained almost universal acceptance after the structure of DNA was elucidated by James D. Watson and Francis Crick in their 1953 Nature publication. Watson and Crick proposed the central dogma of molecular biology in 1957, describing the process whereby proteins are produced from nucleic DNA. In 1962 Watson, Crick, and Maurice Wilkins jointly received the Nobel Prize for their determination of the structure of DNA.
DNA consists of a pair of molecules, organized as strands running start-to-end and joined by hydrogen bonds along their lengths. Each strand is a chain of chemical "building blocks", called nucleotides, of which there are four types: adenine (abbreviated A), cytosine (C), guanine (G) and thymine (T). (Thymine should not be confused with thiamine, which is vitamin B1.) These allowable base components of nucleic acids can be arranged in the polymer in any order, giving the molecules a high degree of uniqueness.
DNA contains the genetic information that is inherited by the offspring of an organism; this information is determined by the sequence of base pairs along its length. A strand of DNA contains genes, areas that regulate genes, and areas that either have no function, or a function as yet unknown. Genes can be loosely viewed as the organism's "cookbook" or "blueprint".
Each base on one strand forms a bond with just one kind of base on another strand, called a "complementary" base: A bonds with T and C bonds with G. Therefore, the whole double-strand sequence can be described by the sequence on one of the strands, chosen by convention. Two nucleotides paired together are called a base pair. On rare occasions, wrong pairing can happen, when thymine goes into its enol form or cytosine goes into its imino form.
The double-stranded structure of DNA provides a simple mechanism for DNA replication: the two strands are separated, and then each strand's complement is recreated by exposing the strand to a mixture of the four bases. An enzyme makes the complement strand by finding the correct base in the mixture and bonding it with the original strand. In this way, the base on the old strand dictates which base appears on the new strand, and the cell ends up with an extra copy of its DNA.