Jl

Deoxyribose

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

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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