Asymmetry of Replication

While biologists will feel at home with the following description of DNA replication, computer scientists may find it overloaded with new terms. If it seems too biologically complex, then feel free to skim this section, as long as you believe us that the replication process is asymmetric, i.e., that forward and reverse half-strands have very different fates with respect to replication.

Movement direction of polymerase

Since a DNA polymerase can only move in the reverse (3′ → 5′) direction, it can copy nucleotides non-stop from ori to ter along reverse half-strands. However, replication on forward half-strands is very different because a DNA polymerase can’t move in the forward (5′ → 3′) direction. On these half-strands, a DNA polymerase must replicate backward toward ori.

Take a look at the figure given below to see why this must be the case.