The standard concentration for absorbance of 1 for ssDNA is 33 ug/ml, while for RNA it is 40 ug/ml. I can't find the reason for the difference in this value for these two macro-molecules. My professor was unable to answer either. Would really appreciate some hint towards finding its answer.

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    $\begingroup$ DNA and RNA have different extinction coefficients - i.e. they absorb different amounts of light - because they have different structures. $\endgroup$ – MelaGo Apr 18 at 7:40
  • $\begingroup$ This paper points out that uridine and thymine have different absorbances at 260, with uridine being higher. Perhaps that helps to explain the difference in absorbances? There seems to be very little difference between ribonucleotides and deoxyribonucleotides. $\endgroup$ – user137 Apr 18 at 7:50
  • $\begingroup$ Another possibility is the ribose-phosphate and deoxyribose-phosphate backbones force different conformations onto the bases, which affects the base stacking interactions. $\endgroup$ – user137 Apr 18 at 8:13
  • $\begingroup$ Thank you user137 for your response. However as you see in my question that actually ssDNA absorbs more than RNA. The paper points to the fact that at 260 nm the absorbance of uridine is higher than thymidine. It also shows that there is negligible difference in the absorbance between ribonucleotides and deoxyribonucleotides if the base is similar in both. So now I am more puzzled by the fact that uridine is absorbing more than thymidine at 260 nm. $\endgroup$ – Arnab Ray Apr 19 at 7:49

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