Direction of DNA Polymerase Activity

Steps:

• In semi-conservative replication, each parental strand templates a new strand.
• DNA polymerase adds nucleotides exclusively to the 3' end of the growing chain.
• This results in synthesis of new DNA in the 5' to 3' direction for both leading and lagging strands.
• The leading strand forms continuously, while the lagging strand forms discontinuously via Okazaki fragments, but both follow the same polarity.

Why D is correct:

• DNA polymerase synthesizes DNA by forming phosphodiester bonds in the 5' to 3' direction, as dictated by the enzyme's active site mechanism.

Why the others are wrong:

• A: Hydrogen bonds form via base complementarity during unwinding; DNA polymerase links nucleotides via covalent bonds.
• B: Polymerase moves 5' to 3' relative to the new strand on the lagging template, not 3' to 5'.
• C: New bases are added to the 3' end of the leading strand, synthesizing in the 5' to 3' direction.

Final answer: D