This model of DNA structure suggested a template mechanism for DNA replication. Watson and Crick proposed that genes on the original DNA strand are copied by a specific pairing of complementary bases, which creates a complementary DNA strand. The complementary strand can then function as a template to produce a copy of the original strand. The two DNA strands separate. Each strand is a template for assembling a complementary strand.
Enzymes link the nucleotides together at their sugar-phosphate groups.
Watson and Crick's model is a semiconservative model for DNA replication. They predicted that when a double helix replicates, each of the two daughter molecules will have one old or conserved strand from the parent molecule and one newly created strand. In the late 1950's, Matthew Meselson and Franklin Stahl provided the experimental evidence to support the semiconservative model of DNA replication. A brief description of the experimental steps is shown in Campbell, Figure 15.8. The helical molecule must untwist while it copies its two antiparallel strands simultaneously.