REPLICATION

Definition of Replication in DNA

DNA replication is the biological process of producing two identical replicas of DNA from one original DNA molecule. This process occurs in all living organisms and is the basis for biological inheritance. The cell possesses the distinctive property of division, which makes replication of DNA essential.

Process of Replication in DNA

1. The first step in DNA replication is to unzip the double helix structure of the DNA molecules. This is carried out by an enzyme called helicase which breaks the hydrogen bonds and holding the complimentary bases of DNA together.

2. The separation of the two single strands of DNA creates a "Y" shape called a replication "fork" and The two separated strands will act as templates for making the new strands of DNA.

3. One of the strands is oriented in the 3’ to 5’ direction (towards the replication fork), this is the leading strands. The other strand is oriented in the 5’ to 3’ direction (away from the replication fork), this is the lagging strand.

As a result of their different orientations, the two strands are replicated differently:

Leading Strand

1. A short piece of RNA called primer (produced by an enzyme called primase) comes along and binds to the end of the leading strand. The primer acts as the starting point for DNA synthesis.

2. DNA polymerase binds to the leading strand and then ‘walks’ along it, adding new complimentary and nucleotide bases (A, C, G and T) to the strand of DNA in the 5’ to 3’ direction.

3. Sort of replication is called continuous.

Lagging Strand

1. Numerous RNA primers are made by the primase enzyme and bind at various points along the lagging strand.

2. Chunks of DNA, called Okazaki fragments, are then added to the lagging strand also in the 5’ to 3’ direction.

3. This type of replication is called discontinuous as the Okazaki fragments will need to be joined up later.