As you well know, DNA molecules consist of two long polynucleotide chains that coiled around each other to form a double helix. The two strands of DNA run in opposite directions to each other and therefore are antiparallel. While direction of one strand is 3’-5’, the other’s is 5’-3’. However, DNA polymerase can only add free nucleotides to the 3’-OH end of primer, to synthesize new strand in a 5’-3’direction. To solve this problem, replication process on 2 strands is performed in a semi-discontinuous manner. On the 3’-5’ parent strand, nascent strand is synthesized continuously, requires only one primer to form leading product. The 3’-5’ template strand therefore called leading template. On the 5’-3’ parent strand, new strand is synthesized discontinuously, requires many primers, resulting short fragments known as Okazaki fragment. Finally, the primer sequences in this newly strand will be removed, and the gap will be filled by polymerase I, and the nick will be fixed by ligase. The 5’-3’ template is called lagging template and its product is lagging product.