Question

1. What are the sequences found in the origin of replication in a bacterial DNA?
2. Explain briefly how DNA polymerases lessen errors in DNA replication.
3. Why are there Okazaki fragments in the lagging strand during replication?

Answer 1

Origins in bacteria are either continuous or bipartite and contain three functional elements that control origin activity: conserved DNA repeats that are specifically recognized by DnaA, an AT-rich DNA unwinding element (DUE), and binding sites for proteins that help regulate replication initiation.

DNA polymerases have proofreading activity that reduces the errors in replication of DNA. Polymerase uses 3' to 5' exonuclease activity to remove the incorrect bases from the 3' end of the new strand. In bacteria, all three DNA polymerases (I, II and III) have the ability to proofread, using 3' → 5' exonuclease activity. When an incorrect base pair is recognized, DNA polymerase reverses its direction by one base pair of DNA and excises the mismatched base.

Okazaki fragments are formed on the lagging strand so that DNA can be synthesized in the essential 5' to 3' manner on the lagging strand. Because these are synthesized in fragments so these fragments lag behind in comparison to leading strand hence its name lagging strand.