Question

You and your lab partners have been given an unknown sample and have determined that its absorbance at 280 nm, in a 1 cm cuvette, is 0.77. (a) Because protein molecules are known to absorb at 280 nm, lab mate A argues that the sample, with its relatively high absorbance at this wavelength, must contain protein. But your other lab mate, B, thinks that the sample is just as likely to contain nucleic acid. What do you think? Explain your reasoning. (b) Describe two experiments that would enable you to resolve this question. Carefully explain how you would interpret the results of these experiments. (c) After holding out for a while, the instructor finally confirms that the sample contains a pure protein sample, with a concentration of 22 µM. Calculate the molar extinction coefficient of the protein, with units of M^-1cm^-1. (d) Next, you are told that the molecular weight of the protein is 45,000 Da. Calculate the protein concentration in units of mg/ml. (e) What is the value of ε for this protein?

          You and your lab partners have been given an unknown sample and have determined that its absorbance at 280 nm, in a 1 cm cuvette, is 0.77.
(a) Because protein molecules are known to absorb at 280 nm, lab mate A argues that the sample, with its relatively high absorbance at this wavelength, must contain protein. But your other lab mate, B, thinks that the sample is just as likely to contain nucleic acid. What do you think? Explain your reasoning. (b) Describe two experiments that would enable you to resolve this question. Carefully explain how you would interpret the results of these experiments. (c) After holding out for a while, the instructor finally confirms that the sample contains a pure protein sample, with a concentration of 22 µM. Calculate the molar extinction coefficient of the protein, with units of M^-1cm^-1. (d) Next, you are told that the molecular weight of the protein is 45,000 Da. Calculate the protein concentration in units of mg/ml. (e) What is the value of ε for this protein?

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