Leading strand refers to a process by which one of the new strand is synthesised by adding nucleotides one by one using a parent strand as template,whereas in lagging strand sysnthesis,nuclotides are added as chunks.Replication can occur easily in leading strand as the enzyme moves along in 3' to 5' direction continously,whereas the lagging strand synthesis is discontinous and takes place in the direction opposite to that the leading strand.
Anyone understanding these feautures think why lagging strand synthesis appears so nonsensical,while there is easy continous way to synthesise strands.
Lagging strand synthesis takes place with a purpose.The need for error correction during DNA replication.A good explanation is given inKleinsmith, LJ. and Kish, VM. Principles of Cell and Molecular Biology, 2nd ed.
Given the complexity of this model, one may wonder why cells don't simply produce an enzyme that synthesizes DNA in the 3' to 5' direction. One possible answer is related to the need for error correction during DNA replication. About one out of every 10,000 nucleotides incorporated during DNA replication is incorrectly base-paired with the template DNA strand. Such mistakes are usually corrected by a proofreading mechanism, which utilizes the same DNA polymerase molecule that catalyzes DNA synthesis. Proofreading is made possible by the fact that the DNA polymerase exhibits a 3'-exonuclease activity, which catalyzes the removal improperly base-paired nucleotides from the 3' end of the polynucleotide chain. This proofreading capability improves the fidelity of DNA replication to the point where an average of only one error occurs for every billion base pairs replicated. If cells did contain an enzyme capable of synthesizing DNA in the 3' to 5' direction, proofreading would not work because a DNA chain growing in the 3' to 5' direction would contain a nucleotide triphosphate at its 5' end. If this 5' nucleotide were an incorrect base that needed to be removed during proofreading, its removal would eliminate the triphosphate group that provides the free energy that allows DNA polymerase to add nucleotides to a growing DNA chain. Hence no further elongation of the DNA chain could take place.
It was Bruce Alberts who gave explanation of how DNA polymerase can replicate both the leading and lagging DNA strands simultaneously. (My next post will be on Bruce Alberts)
Everything has a purpose.