AP BIOLOGY

Detailed explanation-1: -DNA replication takes place at a Y-shaped structure called a replication fork. A self-correcting DNA polymerase enzyme catalyzes nucleotide polymerization in a 5′-to-3′ direction, copying a DNA template strand with remarkable fidelity.

Detailed explanation-2: -DNA is always synthesized in the 5’-to-3’ direction, meaning that nucleotides are added only to the 3’ end of the growing strand. As shown in Figure 2, the 5’-phosphate group of the new nucleotide binds to the 3’-OH group of the last nucleotide of the growing strand.

Detailed explanation-3: -New DNA is made by enzymes called DNA polymerases, which require a template and a primer (starter) and synthesize DNA in the 5’ to 3’ direction. During DNA replication, one new strand (the leading strand) is made as a continuous piece.

Detailed explanation-4: -Replication occurs only in the 5’ to 3’ direction as the incoming nucleotide undergoes nucleophilic attack by the 3’ hydroxyl group of the growing strand at the alpha phosphorus of the 5’ phosphate group. DNA polymerase can therefore only add nucleotides to the growing chain and cannot initiate the replication.