What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?
A) The origins of replication occur only at the 5′ end.
B) Helicases and single-strand binding proteins work at the 5′ end.
C) DNA polymerase can join new nucleotides only to the 3′ end of a pre-existing strand, and the strands are antiparallel.
D) DNA ligase works only in the 3′ → 5′ direction.

Question

Quizplus · Accepted Answer

The leading and lagging strands are synthesized differently because of the antiparallel nature of DNA strands and the requirement for DNA polymerase to add nucleotides only to the 3′ end of a pre-existing strand.

Answer: D 
 DNA ligase can work in both the 3′ → 5′ and 5′ → 3′ directions, so it does not account for the difference in how the leading and lagging strands are synthesized. Choices A and B are also incorrect, as they do not accurately describe the mechanisms for DNA replication.

What Is the Basis for the Difference in How the Leading