Question

DNA strands are antiparallel and replication has adapted to accommodate this. If they were parallel, however, would leading and lagging strands be synthesized in the same way they are in antiparallel DNA? Explain. How would the role of DNA ligase change, if at all?

Answer 1

First of all if the strands of the DNA are parallel to each other then the double helical model of the DNA will not occur as the bases of the DNA that are nitrogen bases are in the opposite direction of each other because of which no hydrogen bond formation will take place and thus, the DNA will have only a single stranded structure. But, even though we consider the case of the mentioned situation then the path followed by the DNA polymerase for the polymerisation and replication of the DNA will be in a single direction than that of the double as the polarity of the strand will remain the same. Thus, the binding of an enzyme will take place on a single side and thus there will not the formation of an Okazaki fragments. However, due to the absence of Okazaki fragments the DNA ligase will only have a role to ligate the RNA primer region to be replaced by DNA and then with the polymerized strand. Here in this case the leading and lagging strand will have a same orientation and thus the two strands will always be the leading and not lagging one.