Practice question

PCR buffer typically contains Tris-HCl, potassium chloride, and magnesium chloride adjusted to pH 8.3-8.8 at 25°C, which shifts to approximately 7.2 at extension temperature due to temperature coefficient of Tris. This system stabilizes pH against proton changes from dNTP hydrolysis, maintains ionic strength required for enzyme activity, and supports polymerase conformation. It does not hydrolyze DNA, dissolve template, or cool reaction, as thermal cycling is mediated by instrument block. Stable pH environment maximizes enzyme processivity, fidelity, and reproducibility across cycles.