It is important to have extra dNTPs and magnesium so the reaction does not run out of components.
dNTPS
- dNTPs are the nucleotide bases added to the growing DNA strand by the DNA polymerase.
MgCl2
- The concentration of MgCl2 influences the stringency of the interaction between the primers and the template DNA.
Salt and buffers
- Stabilize enzyme function and formation of primer template hybrids. Buffers often contain Tris HCl, KCl, and sometimes MgCl2.