Describe how DNA is copied through DNA replication

ASAP TEST REVIEW FOR TOMORROW

DNA replication occurs in the nucleus of the cell inside what are known as replication bubbles. The two DNA strands are separated by an enzyme called Helicase and held apart by another enzyme called Topoisomerase. Whilst held open, a third enzyme, DNA polymerase, slides along one strand of DNA in a 5' to 3' direction - this is the direction that DNA replication must always follow - placing nucleotides to build a matching copy. Similarly the second strand of DNA, known as the lagging strand, is copied by DNA polymerase in the 5' to 3' direction. In order to achieve this, the DNA polymerase must build small sections at a time. These small sections known as Okazaki fragments are then joined together by a final enzyme called DNA ligase.