DNA replicates in order for cells to divide, withy a parent cell divides giving each daughter cell the full DNA string in each nucleus. Without cell division, an organism cannot grow into a plant, a human or an animal. DNA replication allows all cells to contain the full genetic code for the body.
It replicates by unraveling each of the strands of DNA that make up the double helix. Because each of the four nucleotides can only connect to one other, each of the single halves of DNA act as a template to build the other half. The nucleotide thymine can only bond with adenine using two hydrogen bonds, and guanine can only bond with cytosine using three hydrogen bonds.