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Quantifying DNA 2

Quantifying DNA 2 — Concentration to Molarity

 
Starting with a concentration of an oligonucleotide in µg/l, convert this to a molar concentration (molarity) using the length of the oligonucleotide to calculate its molecular weight.

Molarity: nM   
 
You should aim to do these calculations in your head or on a scrap of paper (i.e. without a calculator). The following logic may be helpful:
  • The molecular weight of the oligonucleotide is calculated by multiplying its length by 300.
  • To convert a concentration in g/l to moles/l (M) we divide by the molecular weight. Hence dividing the concentration in µg/l by the molecular weight gives us the concentration in µmole/l (µM).
  • This is multiplied by 1000 to convert from µM to nM.
  • The molarity of the solution is therefore:
    (Concentration x 1000) ÷ (oligo length x 300)
Always do a ‘sanity check’ on your answer. Is it the right order of magnitude? Be suspicious of very high or very low values.