DNA is a molecule made up of strands. Each strand is made up a sequence of four chemical bases that are: , , and . The two strands are . The first step in DNA replication is to both strands. This unzipping is done by an enzyme called and results in the formation of a replication . The separated strands each provide a template for creating a new strand of DNA. An enzyme called makes a small piece of RNA called a that marks the starting point for the construction of the new strand of DNA. An enzyme called [?] binds to the primer and will make the new strand of DNA. DNA polymerase can only add DNA bases in one direction, from the end to the end. One of the new strands of DNA is made continuously, but the other one, called the strand, cannot be made continuously because it runs in the opposite direction. So the DNA polymerase can only make this strand in a series of small chunks called fragments. Each fragment is started with a and DNA polymerase adds a short row of DNA bases in the 5' to 3' direction. The next primer is then added further and the process is repeated until all the lagging strand is completely copied. Once the new DNA has been made the enzyme removes all the RNA primers from both strands of DNA and another DNA polymerase enzyme then fills in the gaps that are left behind with DNA. Finally, the enzyme [?] seals up the fragments of DNA in both strands to form a continuous double strand. DNA replication is described as [?] because each DNA molecule is made up of one old, conserved strand of DNA and one new one.