1. Forty micoliters of a stock solution of RNA is diluted with water to give a f

Question

1. Forty micoliters of a stock solution of RNA is diluted with water to give a final volume of 1000 microliters. The diluted sample has an absorbance at 260nm of 0.142. What is the concentration of the concerntration of the RNA stock solution in micro grams/milliliter.

2. from a small culture, you have purified the DNA of a rocombinant plasmid. You have resuspended the DNA in a volume of 50 microliter. You dilute 20 of the purified DNA sample into a total volume of 1000 microliter distilled water. You measre the absorbance of this diluted sample at 260 nm and 280 nm and obtain the following readings.

A260=0.550

A280=0.324

a. What is the DNA concentration of the 50microliter plasmid prep?

b. How much total DNA was purified by the plasmid preparation?

c. What is the A260/A280 ratio of the purified DNA?

Explanation / Answer

(1) :- Since 40 microliters of RNA is diluted with water giving the final volume of 1000 microliter, so the dilution factor is 1000/40=25.

Now RNA concentration can be calculated by the formula:

RNA concentration (ug/mL) = absorbance reading at 260nm * dilution factor * OD260 unit

OD260 unit value for ssRNA is 40ug/mL

SO RNA concentration can be calculated as:

=0.142*25*40

=142 ug/millilitre

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