Question 3 (1 point)
During DNA replication, one of the new strands of DNA is synthesized continuously.
The other strand is synthesized as a number of separate fragments of DNA that are
subsequently linked by DNA ligase. Why does this occur?

- RNA primers only anneal to one of the parental strands of DNA.

- DNA polymerase III only synthesizes DNA in the 3' - 5' direction.

- DNA polymerase III only synthesizes DNA in the 5'-3' direction.

- One of the parental strands is unwound slower than the other by helicase.

DNA replication is an important phenomenon for every living cell. It is the process whereby the double-stranded DNA is doubled to form two new separate double strands. In order for DNA replication to occur, the double strand of the DNA molecule must first be unwound by an enzyme called DNA HELICASE. This gives two separate single strands, which individually acts as a template for the newly synthesized strands.

DNA polymerase III is the enzyme responsible for synthesizing new DNA strand by pairing complementary nucleotides to the old strands it attaches to. However, one of the old strands called LEADING STRAND runs in the 3'-5' direction while the other strand called LAGGING STRAND runs in the 5'-3' direction.

DNA polymerase III only attaches to the 3' hydroxyll end of the DNA and synthesizes new strand of DNA in the 5'-3' direction. Since the lagging strand runs in 5'-3', it is synthesized in small separate fragments called OKAZAKI FRAGMENTS which are later joined together by an enzyme called LIGASE.

N.B: As DNA polymerase synthesizes DNA strand on the leading strand(5'-3'), it is moving in an opposite direction of the lagging strand. Hence, it has to detach and come back to synthesize on the lagging strand. This causes the lagging strand to be synthesized discontinuously.