Mg2 Dna Polymerase Asp

DNA polymerase

DNA polymerase

MECHANISM FIGURE 25-5 Elongation of a DNA chain. (a) DNA polymerase I activity requires a single unpaired strand to act as template and a primer strand to provide a free hydroxyl group at the 3' end, to which a new nucleotide unit is added. Each incoming nucleotide is selected in part by base pairing to the appropriate nucleotide in the template strand. The reaction product has a new free 3' hydroxyl, allowing the addition of another nucleotide. (b) The catalytic mechanism likely involves two Mg2+ ions, coordinated to the phosphate groups of the incoming nucleotide triphosphate and to three Asp residues, two of which are highly conserved in all DNA polymerases. The top Mg2+ ion in the figure facilitates attack of the 3'-hydroxyl group of the primer on the a phosphate of the nucleotide triphosphate; the lower Mg2+ ion facilitates displacement of the pyrophosphate. Both ions stabilize the structure of the pentacovalent transition state. RNA polymerases use a similar mechanism Nucleic Acid Synthesis

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Essentials of Human Physiology

Essentials of Human Physiology

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