Molecular Evolution and Information

DNA Replication

In order to replicate, the DNA molecule must be untwisted, and the chemical bonds between the base pairs must be broken. This process is controlled by many different proteins. In the first step, a protein binds to the DNA targeting the site to be replicated, another protein untwists the DNA breaking the chemical bonds between the base pairs, other proteins keep the base pair bonds from reforming, and a protein called DNA polymerase replicates the untwisted sections. The two original strands serve as templates (solid lines in figure 3.6) for the growing strands (dashed lines). Figure 3.6 shows how DNA polymerase replicates each strand, creating two DNA molecules from one. Figure 3.6 is simplified in that most of the proteins involved in DNA replication are not shown.


Figure 3.6: DNA Replication







   During DNA replication, sometimes the bases pair incorrectly. That is sometimes adenine pairs with guanine, and thymine pairs with cytosine. Proofreading corrects most of these errors. Thus, DNA replication is very accurate and mistakes are rare, but mistakes happen. Most mistakes just create variability, but some can create information. Mistakes during DNA replication are called mutations.

            

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