Complete Answer

DNA replication begins with the enzyme helicase unwinding the double helix by breaking hydrogen bonds between complementary base pairs. Each separated strand then serves as a template for the synthesis of a new strand. DNA polymerase adds free nucleotides to the new strands, following complementary base pairing rules (Adenine with Thymine, Guanine with Cytosine). Nucleotides are added to the 3′ end, meaning synthesis occurs in a 5′ to 3′ direction. This process is semi-conservative, as each resulting DNA molecule consists of one original (template) strand and one newly synthesized strand.