DNA Replication
We recommend at this point that you watch a video of DNA replication (3:30 minutes). The video will show you the process of DNA replication and describe the enzymes that do the work of DNA replication. We will describe DNA replication and the enzymes in the remainder of this lesson.
In 1953, J.D. Watson and F.H.C. Crick published a note in Nature; one of the world’s most widely read research journals. The note cited just six references (Fig. 8).
Figure 8. The reference list for an article by Watson and Crick in 1953.
Watson and Crick’s writing had limited chemistry details given the title of their note, “A Structure for Deoxyribonucleic Acid”. A later article would share more of the chemistry behind their proposed double helix structure for Deoxyribonucleic Acid (DNA). This note in Nature was written for a broader audience, including biologists who recognized that the structure of DNA was a prerequisite for understanding the function of the genetic material. They included a diagram to allow readers to visualize this unique double helix structure. To emphasize the structure determines function importance, Watson and Crick included this statement in their note…
“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”
Accurate replication prior to cell division is one of the three key functions of the genetic material. While later experiments would reveal the details of how cells replicate DNA, Watson and Crick were obviously impressed that the proposed double helix structure would fit with the concept that living cells are needed to produce more living cells and the transmission of a complete set of biological instructions. The genetic material must have a structure that lends itself to being copied. Using old to help build new leads to a proposed semiconservative model for replicating the double stranded DNA molecule (Fig. 9).
Figure 9. Watson and Crick predicted that the double helix molecule could be replicated in a living cell by the semi-conservative method. Each strand of the template (or old) double stranded molecule is read to build a new strand. Early experiments on replication confirmed this prediction and not the conservative or dispersive methods of replication. Reprinted from DNAreplicationModes by M. Jones, 2005. CC BY-SA 2.5.
Prior to both mitosis and meiosis cell division in multicellular organisms, and cell division in prokaryotes, the DNA inside the cell must be replicated (see lesson Mitosis and Meiosis and the Cell Cycle). This replication process generates the genetic information needed for two cells that are genetically identical to the original cell or, in sexually reproducing organisms, the genetic information to create four gamete cells with half of the original cell’s genetic information.