Answer:
- First, the DNA double helix must be unwound and separated by an enzyme called helicase, creating two separate strands of DNA. These single strands serve as templates for the new DNA strands that will be built.
- DNA polymerase then begins building new DNA strands by adding nucleotides to the template strands. The nucleotides contain a sugar molecule, a phosphate group, and a nitrogenous base, which can be adenine (A), thymine (T), cytosine (C), or guanine (G).
- Importantly, DNA polymerase can only add nucleotides to the new strand in the 5' to 3' direction, meaning that nucleotides are added to the 3' end of the strand. This is because the phosphate group at the 5' end of the nucleotide must bond with the hydroxyl (OH) group at the 3' end of the previous nucleotide in the strand.
- The process of adding nucleotides to the new strand requires complementary base pairing, where each nucleotide added must pair with a nucleotide on the template strand. Adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G).
- As DNA polymerase adds new nucleotides to the new strand, it proofreads its work to ensure that the correct nucleotides are added and that any mistakes are corrected. This process of proofreading helps to maintain the accuracy of DNA replication.