What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesised?
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 difference in how the leading and lagging strands of DNA molecules are synthesized is based on the fact that DNA polymerase can add new nucleotides only to the 3′ end of a pre-existing strand. Therefore, the leading strand, which runs in the 5′ to 3′ direction, can be continuously synthesized in the 5′ to 3′ direction, while the lagging strand, which runs in the opposite 3′ to 5′ direction, must be synthesized in short fragments called Okazaki fragments. These fragments are later joined together by DNA ligase to complete the lagging strand synthesis.

What Is the Basis for the Difference in How the Leading