DNA Polymerase

Copyright: Garland Science
06 1 DNA Polymerase

DNA polymerase faithfully replicates DNA by using the nucleotide sequence of the template strand, colored yellow, to select each new nucleotide to be added to the 3' end of a growing strand, colored gray. In this animation, the different domains of DNA polymerase are colored differently. Before a nucleotide can be incorporated into DNA at the 3' end of the growing strand, the blue finger domain of the polymerase moves inward to correctly position the nucleoside triphosphate. A pyrophosphate group is released when each nucleotide is added. In this view, the details of nucleotide selection at the active site are shown with the incoming nucleoside triphosphate and the template nucleotide in light blue. The growing strand is green, and the template strand is red. When the finger domain moves inward, the nucleoside triphosphate is tested for its ability to form a proper base pair with the template nucleotide. When a base pair forms, the active site residues catalyze the covalent addition of the new nucleotide to the 3' hydroxyl group on the growing strand, and the entire process repeats at speeds up to 500 nucleotides per second. On rare occasions, approximately once every 10,000 nucleotide additions, the polymerase makes an error and incorporates a nucleotide that does not form a proper base pair onto the end of the growing strand. When this occurs, the polymerase changes conformation, and transfers the end of the growing strand to a second active site on the polymerase, where the erroneous, added nucleotide is removed. The polymerase then flips back to its original conformation, allowing polymerization to continue. As a result, such a selfcorrecting DNA polymerase will make a mistake only about once every 107 to 108 nucleotide pairs.