2) If a sample has A280= 0.5 and A260= 0.04, what would be the protein concentra

Question

2) If a sample has A280= 0.5 and A260= 0.04, what would be the protein concentration (mg/ml)?

3) Two tubes, tube 1 containing 0.1 ml of a unknown protein sample and tube 2 containing 0.1 ml of 2 mg/ml BSA standard were subjected for protein concentration by the Biuret method. Absorbance were 0.25 and 0.2 for tube 1 and tube 2, respectively. What is the concentration of protein in the unknown sample in mg/ml?

4) A 20 L diluted sample (1:15) of protein was added to 2 ml of Bradford reaction assay tube. The absorbance at 595 was 0.75 and according to a BSA standard curve corresponding to 0.025 mg protein on the x-axis. What is the protein concentration (mg/ml) of the original protein?

5) What is the theoretical absorbance at 340 nm of a 0.02 M solution of NADH, assuming a 1 cm pathlength (Extinction Coefficient of NADH is 6220 M-1 cm-1 at 340 nM).

Explanation / Answer

Beer-Lambert law which relates absorbance to concentration using the path length of the measurement and an extinction coefficient as follows

          A = c l

Where A = absorbance, = molar extinction coefficient, c = concentration and l = light path length

A = c l

0.41 = 8.2x103M-1cm-1 * c*1 cm

c= 5.0*10^-5 M

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