This is a four stage process, during which a double-stranded DNA molecule is copied in order to produce two identical DNA molecules. During the first stage, the replication fork is formed, so the DNA molecule can be 'unzipped'. The second stage consists of a short piece of RNA called a primer binding to the 3' end of the strand and it always binds as the starting point for replication. After this, DNA polymerases create the new strand via elongation. 5 different known types of DNA polymerases exist in bacteria and human cells. Replication proceeds in the 5' to 3' direction on the leading strand and that's why the newly formed strand is continuous. When the continuous and discontinuous strands are formed, exonuclease removes all RNA primers from the original strands. These primers are then replaced with appropriate bases. Furthermore, different exonuclease examines the newly formed DNA to check, remove and replace any errors. Once completed, the parent strand and its complementary DNA strand coils into the double helix shape. Finally, replication produces two DNA molecules, each with one strand from the parent molecule and one new strand.