You have purified total RNA from leaf cells of a maple tree. You dissolved all t

Question

You have purified total RNA from leaf cells of a maple tree. You dissolved all the RNA in 50 ul (microliters) of pure water to make an "RNA Sample." You need to determine the concentration (ug/ul) of this RNA sample, to do this you removed 2 ul from the sample and added these to 998 ul of water and put in a cuvette. You determined the absorbance of light at 260nm for this 1ml of RNA water solution in the cuvette and the A260 value was 0.058. A260 of 1.0 = 40 ug/ml for RNA.

i) what is the concentration (ug/ul) of the RNA in the cuvette?

ii) what is the concentration (ug/ul) of the RNA in the original RNA sample?

iii) How many ul of the RNA sample would you need to use in an experiment that required a total of 10ug RNA?

Explanation / Answer

2 L + 998 L = 1000 L = 1 mL

Since an absorbance of 1 = 40 g/mL 40 g/mL x 0.058 = 2.32 g/mL = 2.32 x 10-3 g/L

Since the only source of RNA was the original 2 L sample, then the RNA sample could be said to be 2.32 g/2 L = 1.16 g/L

Since there are 50 L in the original RNA sample, then 50 L x 1.16 g/L = 58 g of total RNA in the initial 50 L sample.

If a total of 10 g were required for an experiment, and the original sample was 1.16 g/L, then

10 g / 1.16 g/L = 8.62 L of RNA Sample would be required.

So, the answers are:

i) 2.32 x 10-3 g/L    

ii) 1.16 g/L

iii) 8.62 L of RNA Sample would be required

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