Atransposon inserts into a single origin of replication (ori) in a eukaryotic cell and prevents helicase from binding the ori. how does this affect replication at this particular ori and how is cell division affected?

In the given case, replication will not begin from the mentioned origin of replication, however, the overall rate of cell division will be quite normal. As mentioned, if helicase fails to bind with the ori, the unwinding of DNA would not take place, this further prevents the replication of DNA.  

However, the eukaryotic cells exhibit various origins of replication. Thus, the loss of a single origin of replication is unlikely to exhibit a huge influence on the overall rate of cell division.  

b brown mice / white sand dunes