The DNA polymerase Mechanism

DNA polymerases have a common mechanism for DNA chain synthesis. During replication, both strands of the duplex DNA molecule serve as templates. The DNA strands are separated, and each of the DNA strands is copied. This process results in two identical copies of the original duplex DNA molecule being produced for the two cells. The DNA polymerase uses the nucleoside triphosphates form of the deoxynucleotides to build the DNA polymer. The monophosphate form of the deoxynucleotide is incorporated into the growing DNA chain, and a pyrophosphate molecule released. The DNA polymerase can add nucleotides only to the 3′-OH end of the growing DNA chain. Therefore, DNA polymerization occurs in only one direction. Some DNA polymerases are highly possessive, means they can add many nucleotides to the 3′ end of the DNA chain before falling off the DNA template. Other DNA polymerases are distributive in nature means incorporating just one nucleotide and then falling off the DNA template.
Like other proteins, the DNA polymerases are encoded by certain genes. Analysis of this sequenced human genome shows that there may as many as fifteen different DNA polymerase genes in the human genome. A similar analysis of the Escherichia coli genome shows that there are five different DNA polymerase genes present in this bacterium. This indicates that number of DNA polymerases increases with increasing complexity ans specialization of each polymerase for a peculiar role in various aspects of DNA replication and repair . The overall catalytic subunits of DNA polymerases is very conserved from species to species Which indicate their irreplaceable functions in the cell, the maintenance of which provides evolutionary advantages. The DNA polymerases range in size from just over three hundred amino acids in length to more than two thousand amino acids in length. DNA polymerases are found in the regions where the enzyme contacts the DNA molecule.