Question

You do a series of incubations to compare the properties of E. coli DNA polymerase I and III. After incubating DNA template prepared from bacteriophage T7 with one or the other polymerase for 20 min, you add an excess of a second template, phage T3 DNA and continue the reaction for a further 40 min. You compare the amounts of T3 synthesized to the amount of T7. Most of the DNA synthesized in the polymerase I incubations is found to be T3 DNA, but almost all of the DNA in the polymerase III incubation is T7 DNA. Can you explain these results?

Answer 1

DNA polymerases are specially designed enzymes which help in formation of DNA molecules by assembling tiny building blocks of DNA called as nucleotides. DNA polymerase helps in splitting of the DNA molecule into two identical DNAs. This process of DNA splitting is called as DNA replication. DNA polymerase act as a catalyst in DNA replication and hence is very essential. DNA polymerase helps in reading the already existing DNA strands to create two new strands that match the original existing DNA. In this way, the genetic information is forwarded into the daughter cells and transmitted from one generation to another.

DNA polymerase 1 functions helps in DNA replication. It is used for molecular biology research. During the process of replication, an RNA primer is filled in the lagging strand of the DNA. DNA polymerase 1 removes the RNA primer and fills in the nucleotides which are necessary for the formation of the DNA in the direction- 5’ to 3’. It also helps in proof reading to see if there is any mistake done while replication and while matching base pairs. The fact that must be remembered is that this DNA polymerase 1 only adds the nucleotides but does not join them. DNA joining is done by another enzyme called as ligase which forms continuous strands of DNA. The main function of DNA polymerase 1 is DNA labeling by nick translation and second strand synthesis of cDNA. DNA polymerase 1 also catalyzes 5’ to 3’ synthesis of DNA. DNA polymerase 1 reads the shape and polarity of the incoming dNTP. DNA polymerase 1 has 3 activities like polymerase, 3’ to 5’ exonuclease and 5’ to 3’ exonuclease. DNA polymerase 1 is a template dependent DNA polymerase.

DNA polymerase 1 aslo called as taq polymerase which is use in PCR technique and it isolated thermus aquaticus which is a thermeal bacteria so it is resistant polymerase having three types of activities such as 3' to 5' exo nad endonuclease activity and 3'to 5'polymerasd activities also present so

The Pol 3 catalytic centre has tightly bound subunits called alpha, epsilon and theta. The alpha subunit is responsible for the DNA polymerase activity, the epsilon subunit has proof reading exonuclease activity and the theta subunit is the smallest of all and helps in enhancing the proof reading properties of epsilon. A Replisome is located at the replication fork. DNA polymerase 3 is a component of the replisome and hence helps in replication.

The plymerase in distinct organisms contains different types of work in distinct way so in case of T3 andT7 bactriophage have different polymerase activity in case of T3 DNA POLYMERASE 1 and the incubation period also matter so that different amounts of DNA synthesized in bactriophage have been seen