Figure 2.

Chemistry of DNA synthesis. The 3’ OH terminus of the primer strand (top strand) is activated for nucleophilic attack on the alpha phosphate of an incoming dNTP, with release of PPi. The reaction involves two metal atoms (blue) that are bound within the active site of the polymerase (yellow). The metal atoms facilitate proton removal from the 3’ OH, and stabilize the pyrophosphate leaving group (see color version of this figure at www.informahealthcare.com/bmg).