After Watson and Crick's discovery of the structure of DNA, the mechanism by which it was copied before cell division was investigated.
Watson and Crick proposed that DNA consists of two
strands, and that these two strands could be separated to allow each one to act as a template for a new strand. Each new DNA molecule would, therefore, contain one original strand and one newly synthesized strand, a model known as
replication. This model was later shown to be correct by an experiment conducted by
In 1963, John Cairns studied the replication of the DNA in the chromosome of the bacterium E. coli. He showed the chromosome is
, that replication begins at
, and that replication proceeds
from each origin.