It has been a while since biology...but if there is one thing I definitely remember, it is the replication process of DNA.
Once the cell is ready to commence the process of replication, it begins by unzipping the double helix. This task is completed by an enzyme called the DNA Helicase. Then a DNA Polymerase takes half of the unzipped DNA strand and creates corresponding deoxyribonucleotides.
Hope I could help! Have a good one.