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DNA is the carrier of genetic information, so DNA in the cell must be duplicated and passed down to the daughter cellsaccurately. Thus, the DNA in the cell duplicates through the process of DNA replication.

In a replicating DNA molecule, the two strands are antiparallel (5’ to 3’ and 3’ to 5’) at the replication fork. The strand with its 3’OH oriented toward the fork is elongated by the sequential addition of new nucleotides to this end. This strand is called the leading strand or continuous strand and is synthesized in the 5’ to 3’ direction.

The other strand is called the lagging strand because this strand grows by synthesizing short fragments or Okazaki fragments and the subsequent joining of these fragments.

A group of enzymes that are involved in the synthesis of DNA molecules is called DNA polymerases.There are three types of DNA polymerases involved in DNA replication: DNA pol I, II, and III. However, DNA polymerase III is the main enzyme involved in DNA replication.

DNA pol III is the polymerase that catalyzes the synthesis of a new strand of DNA using the template strand of the old DNA molecule.

In the replication fork, primase adds RNA primer complementary to the template strand. After adding RNA primer, DNA pol III attaches to the DNA strand and starts adding nucleotides to the RNA primer.

It then continuously adds nucleotide to the growing strand using the parental template strand, thereby synthesizing the continuous strand of the DNA molecule. Similarly, it adds nucleotide to the RNA primer of the lagging strand.

To synthesize the lagging strand in the 5’ to 3’ direction, it works opposite to the replication fork strand. Thus, the polymerizing activity of DNA is referred to as 5’ to 3’ polymerization as it directs the synthesis of the strand in a 5’ to 3’ direction.