Solution Preparation Techniques in Molecular Biology
Common Conversions in Molecular Biology
1 gram (g) = 1 X 103 milligrams (mg) 1 liter = 1 X 103 milliters (mL)
1 gram (g) = 1 X 106 micrograms (mg) 1 liter = 1 X 106 microliters (mL)
1 gram (g) = 1 X 109 nanograms (ng) 1 liter = 1 X 109 nanoliters (nL)
1 gram (g) = 1 X 1012 picograms (pg) 1 liter = 1 X 1012 picoliters (pL)
1 molar solution = 1 mole/liter
Preparation of Molecular Biology Solutions
A. Making working solutions from stock solutions
Many solutions used in molecular biology are contained as stock solutions. Stock solutions typically must be diluted with distilled water (dH2O) making 1X working solutions
For example, TBE buffer widely used in agarose gel electrophoresis comes many times as a 100X stock solution. TBE buffer is used in electrophoresis runs as a 1X working solution. Suppose you want to make 1 liter of a 1X TBE solution using a 100X stock solution. How would you do it?
Use the algebraic equation C1V1 = C2V2 where C = concentration of solution and V = volume of solution.
To make 1 liter of a 1X TBE solution, C2 = 1X TBE, V2 = 1 liter and C1 = 100X TBE. The concentration of the 100X TBE solution is V1.
V1 = 1X TBE(C2) x 1 liter (V2) / 100X TBE (C1).
V1 = 0.01 liters or 10 milliters. Add 10 mLs of 100X TBE to 0.990 liters or 990 milliliters of distilled water. Mix and now you have 1 liters of a 1X TBE solution.
B. Making Molar Solutions.
Many molecular biology solutions are made as molar
solutions. Remember that 1 molar = 1 mole/liter.
To make this solution, you need to know the molecular weight of Sodium Chloride (NaCl). The molecular weight should be written somewhere on the container containing NaCl powder. The molecular weight of NaCl is 58.44 grams/mole.
To determine how much NaCl one needs to make up 500 mLs of a 1 molar solution do the following.
58.44 grams /mole X 1 mole/liter X 0.5 liter = 29.22 grams of NaCl. Note that the moles and liters cancel out.
Weigh out this many grams of NaCl and mix with distilled water in a beaker up to the 500 mL line. Stir by mixing. Now you have 500 mLs of a 1 M NaCl solution.
Working solution exercises.
1. Many restriction enzyme buffers come as 10X stock solutions. How much of a 10X restriction enzyme buffer is needed for a 50 mL DNA-enzyme digestion?
Note that 1 molar = 1000 mMolar.
The molecular weight of NaHCO3