Spectroscopy is a useful tool to determine the concentration of DNA in a solution by measuring the UV absorbance at a wavelength of 260nm. When analyzing the purity of a DNA sample, an additional measurement of UV absorbance at 280nm is often taken to determine if proteins are is present as well. The ratio of 260/280 is then taken, and the closer this value is to 2 the more pure your DNA sample. a) Given that the aromatic rings present in the nitrogenous bases of DNA cause DNA to absorb UV light at 260nm, predict what might be responsible for proteins absorbing UV light at 280nm. b) You purify two DNA samples and measure the absorbance at 260nm and 280nm. For the first sample (Sample A) the absorbance at 280nm is 0, and for the second sample (Sample B) the absorbance at 260nm is 0.5. You are skeptical that Sample A is really that pure, and upon further testing you identify contaminating protein sequences (shown below) in both samples! Sample A contaminating protein: MSTSILEGAASTL Sample B contaminating protein: MLYSWAFEWEYSFWL Explain why the contaminating protein in Sample B does have an absorbance at 280nm, while the contaminating protein in Sample A does not. c) The energy gap between the relevant electronic levels for DNA absorbance at 260nm is (bigger/smaller) than the gap for protein absorbance at 280nm by ____________.
Spectroscopy is a useful tool to determine the concentration of DNA in a solution by measuring the UV absorbance at a wavelength of 260nm. When analyzing the purity of a DNA sample, an additional measurement of UV absorbance at 280nm is often taken to determine if proteins are is present as well. The ratio of 260/280 is then taken, and the closer this value is to 2 the more pure your DNA sample.
a) Given that the
b) You purify two DNA samples and measure the absorbance at 260nm and 280nm.
For the first sample (Sample A) the absorbance at 280nm is 0, and for the second sample (Sample B) the absorbance at 260nm is 0.5. You are skeptical that Sample A is really that pure, and upon further testing you identify contaminating protein sequences (shown below) in both samples!
Sample A contaminating protein: MSTSILEGAASTL
Sample B contaminating protein: MLYSWAFEWEYSFWL
Explain why the contaminating protein in Sample B does have an absorbance at 280nm, while the contaminating protein in Sample A does not.
c) The energy gap between the relevant electronic levels for DNA absorbance at 260nm is (bigger/smaller) than the gap for protein absorbance at 280nm by ____________.
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