Model of E.coli replication fork

A replication fork is formed during the replication of the DNA and is initiated by the enzyme helicase which breaks the hydrogen bond formed between the nucleotides thus separating the strands. The two strands will act as a template for leading and lagging strand, during replication. In the leading strand, replication is carried out in 3’ to 5’ direction allowing the new strand to be synthesized 5’ to 3’. The DNA polymerase continuously reads and adds nucleotides to the growing strand. In the lagging strand, the replication fork moves in 5’ to 3’ direction and the growing strand is synthesized 3’ to 5’. Since DNA polymerase catalyzes the polymerization of dNTPs only in the 5′ to 3′ direction, therefore the enzyme primase reads the DNA and adds short segments of RNA to it. DNA polymerase lengthens the segments and Okazaki fragments are formed which are joined by DNA ligase. Thus with the help of leading and lagging strand the replication form moves forward till the total DNA is replicated.