Why DNA Polymerase III Holoenzyme can synthesize DNA with very high processivity?

While Polymerase III core with the polymerase activity resides on the α subunit can only synthesize DNA with 10–20 nucleotides per binding event, replicative DNA synthesis by pol III holoenzyme is highly processive. This rapid increment in processivity of Pol III Holoenzyme is enhanced by β subunit. The β subunit is a doughnut-shaped dimer that can form a ring around DNA and functions as a sliding clamp that inhibits dissociation of pol III core from DNA during chain elongation. By this, Pol III Holoenzyme can synthesize more than 5 Continue Reading →

DNA Polymerase III Holoenzyme

Pol III Holoenzyme is a big molecule that consists of 10 different subunits. Three subunits alpha, epsilon and theta form the core and there are 2 cores in a Pol III Holo enzyme complex that linked by tau subunit. Each core is responsible for leading and lagging synthesis. The gamma complex (clamp loader) is composed of gamma, delta, delta prime, chi and psi subunits; take in charge in loading beta clamp onto primed DNA. The complex consist of two cores and the gamma complex is called as Polymerase III*. When beta clamp is added to each Continue Reading →

Overview of 5 DNA polymerases in E. coli cell

So far, there are 5 distinct DNA polymerases have been found in E. coli cell: Pol I, Pol II, Pol III, Pol IV, and Pol V. While Pol III (Pol III Holoenzyme) is a primary polymerase involved in DNA replication, the others take part in other processes such as DNA repair, translesion synthesis … rather than in chromosome replication. Pol I is encoded by polA gene and belongs to the A family. During DNA replication, PoI synthesizes the gap between Okazaki fragments to complete lagging product synthesis by its 5′-3′ polymerase activity. Continue Reading →

Why DNA replication is semi-conservative?

DNA replication is a complicated biological process which generates two identical copies of DNA from an original one. During DNA replication, double stranded DNA molecule is unwound by enzyme helicase, and each separated single strand will be used as template (parental strand) for the synthesis of a new strand (daughter strand). Synthesis of each daughter strand is done by the addition of free nucleotides complementarily to the parental strand. As the result,  two new double stranded DNA molecules will be formed, in which, in each molecule, one strand is the Continue Reading →

What is replication fork?

During DNA replication, double stranded DNA is unwound by enzyme helicase. This unwinding process generates a Y-shape structure which exposes 2 separated single strands after helicase movement. Each separated single stranded DNA is used as template (leading and lagging template) for DNA synthesis by polymerase. The junction between the newly separated template strand and the double stranded DNA in front of helicase is called Replication Fork (RF). Based on the replisome structure, replication fork is also defined by the point where both unwinding activity of helicase Continue Reading →

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