The structure of DNA

Soon afterward, in 1953, James Watson and Francis Crick, from Cambridge University, presented their theory for the three-dimensional structure for DNA, a giant milestone in science. They proposed that DNA consists of two chains that wind around each other in a helical orientation (refer to Figure 2.2 in Chapter 2) and are held together by weak bonds between hydrogen atoms located on the four nucleotides. These bonds held the strands in place but also permitted them to separate for the next round of replication.

Proof for the unzipping process of DNA replication, as suggested by Watson and Crick, came five years later with the elegant work of Meselson and Stahl (see the following sidebar).