Lab 1 1. How is spectrophotometry used in measuring nucleic acids? Answer: The presence of aromatic rings in the purines and pyrimidines gives the intense absorption of light wiaves in the UV light. 2. How to calculate the final concentration of a nucleic acid sample Answer: Concentration: 50 μ g/1ml x 1 mg/1000 μ g x dilution of sample 1 x A260 Ex 2) 40 μ g/1 ml x 1 mg/1 μ g x A260 x dilution of sample 2 To calculate the concentrations of these nucleic acid samples you take the expected concentration, multiply it to be in terms of micrograms, then multiply that by the dilution (1:50, 1:200 etc) and finally multiply that number by the absorption at A260. (note: the “expected concentration” of DNA is 50 µg/mL RNA is 40µg/mL and oligonucleotides are 33 µg/mL 3. How is the purity of nucleic acid samples assessed? Answer: Absorbance’s at A 260 cannot discriminate between DNA and RNA: so using the ratio between the A 260
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