Molecular Basis of Cellular Information:
The Structure of DNA and its Replication

Reproduction is one of the fundamental characteristics of living organisms. The process of reproduction can be viewed at different levels: organisms can duplicate themselves by asexual and/or sexual reproductions; cells can duplicate themselves by cell divisions; and genetic materials can duplicate themselves by replications.

In 1953, Watson and Crick proposed the structure of DNA as two strands of helix intertwine each other, which are held by hydrogen bonds between their bases. Since these bonds are weak and readily broken, Watson and Crick envisioned that DNA replication can be occurred by gradual separation of the strands of the helix, much like the separation of two halves of a zipper. In addition, since the two strands are complementary to each other, each strand contains enough information for the reconstruction of the other strand. Therefore, once the strands are separated, each strand can serve as a template to direct the assembly of nucleotides needed for forming the complementary strand, and restoring the original double-stranded state (semiconservative replication).

As evolution progressed, DNA molecules had replaced RNA molecules as the primary storehouse of genetic information. The process of replication became considerably more complex, and required a large number of auxiliary components in order to make the process to proceed not only more efficiently but also more accurately.