The process of making an exact copy of DNA before the cell divides is called DNA Replication. Before the division, all cells must go through this process to make sure that the genetic information they contain is available for the production of proteins when needed.
The field for the DNA replication process is different for eukaryote cells and prokaryote cells. For earlier ones, it mostly happens within the nucleus, however for the latter ones, the location is cytoplasm. No matter what be the location, the activities are very much alike and the reason is the same, i.e. the cell (parent) has to make an exact copy of DNA to transfer its all characteristics and information to the new cell (daughter).
DNA replication happens all the time in our body but significantly important is that, life begins and depends on it as an embryo uses DNA and RNA (similar structure as DNA with small difference) instructions to grow and become an organism. This new organism has all the characteristics of its parents, for this reason a human has a human baby and a plant produces seeds.
Before going deeper into the precise details of DNA replication, it is very important to learn some basics about DNA Structure. However, since we have covered it in another article, we are not going to repeat it here. Instead, we are going to present a bird eye-view of the DNA replication process.
Prior to cell division, double helix splits up, exposing the bases to RNA in the cytoplasm. RNA starts attaching with bases. This process is bi-directional as it happens on both ends of the replication fork (a notch where DNA replication starts) simultaneously in different directions. In one strand it pairs up in fragments called Okazaki fragments.
When the replication is done, fragments start joining. Finally they re-coil into double helix. As two strands of DNA are copied simultaneously, so the original DNA makes two copies of itself by each strand. The replicated DNA in new cells is considered as semi-conservative, because it has 50% of the original genetic matter taken over from its parent.
Changes in DNA replication cause minor or fatal results. Once the DNA is mutated, it would copy itself as truly as the original one so the mutated organism would transfer its defects to its offspring. Consequently some heredity diseases transfer from generation to generation, and some diseases like cancer spreads in the infected body only.