Question

A small linear chromosome has a single origin of replication, which is located at the exact center of the chromosome. If the origin was located at one of the ends of the chromosome instead, what effect would this have to the length of time it takes to complete the duplication of this chromosome?

Answer 1

When the origin of replication is at the center of the DNA fragment, for each strand, half of the DNA synthesied is in the direction of the lagging strand and half in the leading strand. Thus, it takes an equal amount of time per strand. However, when the origin of replication is at the end of the fragment, one strand is replicated entirely by the lagging strand, which takes longer than the leading stand. Overall, because of the longer time taken by the synthesis of the lagging strand, the latter takes longer to complete the duplication.