Ans. DNA Replication
Before a cell divides, its DNA
is replicated (duplicated). It is done to make the copies of
the chromatids of chromosomes. During replication, the DNA double helix is unwound and the two strands are separated, much like the two sides of a zipper. Each strand acts as a template to produce another strand. Its N bases, (nitrogenous bases) make pairs with the N-bases of new nucleotides. In this way, both template strands make new
polynucleotide strands in front of them. Each template and its new strand together then form a new DNA double helix, identical to the original. Figure 15.3