Since Taq polymerase cannot function without free magnesium ions (Mg++)and many chemical species can bind Mg++, a gross excess of Mg++ must always be added to any PCR reaction mixture.

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Quizplus · Accepted Answer

While it's true that Taq polymerase requires free magnesium ions to function and that various substances can bind Mg++, adding a gross excess of Mg++ is not always necessary. The optimal concentration of Mg++ varies depending on the specific reaction conditions and components, and too much Mg++ can actually reduce the specificity and yield of the PCR by increasing nonspecific amplification.

Since Taq Polymerase Cannot Function Without Free Magnesium Ions (Mg++)and