Question

Recall that dilution factors can be used with concentrations of solutions as well as with titers of cell suspensions. A molecular biologist sets up a PCR reaction containing 5.0 µl of primer mixture, 1.0 µl of dNTPs, 1.0 µl of Taq polymerase, 10.0 µl of 5X buffer, 20.0 µl of extracted DNA solution, 3.0 µl of 25 mM MgCl2 and 10.0 µl of sterile water. What would be the final concentration in mM of MgCl2 after the components are mixed?

Answer 1

Answer:

1.5 mM

Explanation:

PCR mix

• 5 µL Primers
• 1.0 µL dNTPs
• 1.0 µl Taq pol
• 10.0 µl of 5X buffer
• 20.0 µl DNA
• 3.0 µl MgCl₂ 25mM

• 10.0 µl H₂O

Total volume = 50 µL

We can use the dilution factor (df) to calculate the final concentration of MgCl₂

$\frac{Initial\ concentration}{dilution\ factor}  = final\ concentration$

The dilution factor can be calculated as the final volume divided by the sample volume.

• Final volume = 50 µL of PCR mix
• Sample volume = 3 µL of MgCl₂
• Dilution factor = 50 µL / 3 µL = 16,67

The final concentration of MgCl₂ in the mix will be:

$\frac{25\ mM}{16.67} = 1.5\ mM$