Semidiscontinuous DNA replication

O As the helix unwinds, the other parental strand (the 5 — 3 strand) is copied in a discontinuous fashion through synthesis of a series of fragments 1000 to 2000 nucleotides in length, called the Okazaki fragments the strand constructed from Okazaki fragments is called the lagging strand. 

This universal nature of synthesis presents a problem for the cell because as the DNA synthesis proceeds along a rephcation fork, the two strands are going in opposite directions. 

How can replication proceed along the DNA if the two strands are going in opposite directions  

The first DNA polymerase discovered was found in E. coli. DNA polymerase catalyzes the successive addition of each new nucleotide to the growing chain. 

A nucleoside derivative that has been very much in the news is 3 -azido-3 -deoxythymidine (AZT). This compound has been widely used in the treatment of AIDS (acquired immune deficiency syndrome), as has 2 -3 -dideoxyinosine (DDI). Propose a reason for the effectiveness of these two compounds. Hint How might these two compounds fit into a DNA chain  

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