The synthesis of DNA is called replication. DNA replication is the process by which DNA makes a copy of itself during cell division. Replication starts at a particular DNA sequence called an origin of replication or ORI. In prokaryotic cells, the origin is at one site. In eukaryotic cells, the origin is at many sites. There are 3 main stages of DNA replication namely initiation, elongation and termination DNA replication is semi-conservative which means each strand in the double helix acts as a template for synthesis of a new, complementary strand. The key enzyme for DNA replication id DNA polymerase besides this process requires many other enzymes and proteins.