DNA polymerase binds to the leading strand and then ‘walks’ along it, adding new complementary nucleotide bases (A, C, G and T) to the strand of DNA in the 5’ to 3’ direction.The primer acts as the starting point for DNA synthesis. A short piece of RNA called a primer (produced by an enzyme called primase) comes along and binds to the end of the leading strand.Image credit: Genome Research Limited Leading Strand: As a result of their different orientations, the two strands are replicated differently:Īn illustration to show replication of the leading and lagging strands of DNA. The other strand is oriented in the 5’ to 3’ direction (away from the replication fork), this is the lagging strand. One of the strands is oriented in the 3’ to 5’ direction (towards the replication fork), this is the leading strand.The two separated strands will act as templates for making the new strands of DNA. The separation of the two single strands of DNA creates a ‘Y’ shape called a replication ‘fork’.This is carried out by an enzyme called helicase which breaks the hydrogen bonds holding the complementary bases of DNA together (A with T, C with G).The first step in DNA replication is to ‘unzip’ the double helix structure of the DNA molecule.
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