How Does DNA Replication Work?

There are four main steps in the replication of DNA. The steps include replication of fork formation, primer binding, elongation and termination. 

Step 1 

Before the replication process of the DNA starts, there is a need to have the strands unzipped from each other. The unzipping of the strands leads to the formation of two strands of the DNA. There are four bases in each of the strands. The bases include adenine, thymine, cytosine, and guanine between the two strands, each of the bases forms pairs. The adenine is only in a position to pair with thymine, and cytosine only binds with guanine. For unwinding to occur, there is a need for the interaction between the pairs to be broken (Aze and Maiorano, 2018). The process takes place with the assistance of helicase, which is an enzyme. The enzyme interferes with the hydrogen bonding that exists between the pairs. The separation of the bases forms a Y-shaped replication fork. After the separation of the bases, the replication process cannot take place. 

Step 2 

The leading strands are the simplest to go through the replication process. After a successful separation of the DNA strands, and RNA is introduced, referred to as primer. The primer connects itself to the three ends of the strand and creates the binding process's starting point. The DNA primase enzyme does the generation of the primers. After the attachment of the RNA to the strands, the elongation process starts to take place. 

Step 3 

The DNA polymerase is responsible for creating new strands through a process known as the elongation. Five types of DNA are present in the human and bacteria cells. There is the E. coli, Polymerase III, which forms the central part of the enzyme in the bacteria. Other polymerases, including polymerase I, II, IV, V, whose primary responsibility is to check for errors and make repairs in the elongation process (Simion, 2018). Polymerase III connects with the strand when the primer has attached itself and starts to add new bases are making the strand longer and thus the name elongation stage. In eukaryotic cells, there are the polymerases alpha and delta that are also a part of the replication process. The formation of the new DNA strand is continuous. There is a lagging phase in step three, where the lagging strands start taking place through a binding process that involves several strands. Each of the primers will have several bases apart from each other. The DNA polymerase will then add the Okazaki fragments to all the strands but in between the primers. The process then comes to a halt; the new fragments are disconnected from each other. 

Step 4 

Once there is the discontinuation of the process, the exonuclease enzyme comes into play. The role of the enzyme is to remove the primers from the original strand. Bases then replace the spaces which were occupied by the primers. Proofreading of the new forms of DNA takes place to check if the bases match each other and remove any errors that might have taken place (Simion, 2018). Enzyme DNA ligase combines with the fragments and forms a single strand that is unique and uniform. Telomerase then catalyzes the creation of telomere at the end of the DNA strands. Once the process is incomplete, the two strands coil each other and create a double helix shape. At the end of the replication process, there are two DNA molecules, each having a strand from the parent molecule and one new strand created in the process. 

References 

Aze, A., & Maiorano, D. (2018). Recent advance in understanding DNA replication: Cell type-specific adaptation of the DNA replication program. F1000 Research, Article Review, 7, 1351. 

Simion, T. (2018). DNA replication. Current Trends in Biomedical Engineering and Bioscience, 16(4), 1-7.