Question

Q5: (2) DNA quantitation. You measure the absorption spectrum for a sample of DNA and obtain the values listed below. The DNA had been diluted 10 fold. Remember that a solution of DNA that is 50μg/ml (or 50ng/μl) has an absorbance of 1.0 at a wavelength of 260 nm. What is the concentration of the DNA in this sample (In this question DO NOT ignore the problem of dust in the sample and give answer in ng/ul).

A₂₆₀ = 0.80                  A₂₈₀ = 0.40                  A₃₂₀ = .05        A₂₃₀ = 0.40

Answer 1

Nanodrop takes the measurement at 260nm.

The ratio of 260/280 gives us details about the DNA quality.

If the ratio is between around 1.8, DNA is considered pure. Below 1.8 ratio DNA has the contamination of protein and phenol.

Given that A₂₆₀ = 0.80 and A₂₈₀ = 0.40     

Ratio of 260/280 is 2. So DNA is not pure.

Absornace at 260 is 0.8.

So the concentration of DNA is 0.8*50 = 40ng/ul,

DNA was diluted 10 times before taking the reading on Nanodrop.

So DNA concentration in the original DNA sample is 10*40 = 400ng/ul.