Replication of DNA

        Assalamualaikum and hi everyone. Today, we will discuss how DNA can replicate themselves to form a new strand. Basically, DNA replication is a process of copying DNA molecules. During replication, the original strands serve as templates for synthesis the new DNA. Although this process will create new DNA strands, it is considered as semiconservative because one of the original strands is present in each new DNA helix. Each daughter DNA molecule consists of one new chain of nucleotides and one from the parents DNA molecules. The new daughter DNA molecule will be identical to the parent molecule.

          The picture above shows steps in DNA replication. Basically, there are three main steps in DNA replication such as initiation, elongation, and termination. In the first step, it starts at a point called oriC which certain initiator protein bind and start to unwind the DNA double helix structure. Besides that, the presence of an enzyme called as helicase also helps in the process of unwinding the DNA structure. This process is important as they will prepare the DNA for the next steps.
          Next, for elongation, new DNA strands will be synthesised from 5' - 3' end based on the direction of template strand which is 3' - 5' end by an enzyme called DNA polymerase III.  On each old DNA strands, the DNA replication occurs differ with each other. For leading strand, it was synthesised continuously from 5' - 3' and moving toward the replication fork as the template strand starts from 3' - 5' end. Meanwhile, for lagging strand, it will be synthesised semi-discontinuously as small fragments from 5' - 3' end but moving away from the replication fork. These small fragments are called as Okazaki fragments. First, RNA primer will be synthesised by primase then extended into Okazaki fragments before being linked together by DNA ligase.
           After all of the bases are matched up (A with T, C with G), termination will take place. An enzyme called exonuclease will strips away the primers. The gaps where the primers had left will be filled by yet more complementary nucleotides. The new strand is proofread to make sure that there are no mistakes in the new DNA sequence.The result of DNA replication is two DNA molecules consisting of one new strand and one parent strand. This is the reason why DNA replication described as semi-conservative as half of the chain is part of the original DNA molecule, half is brand new strand.