The same DNA strand is added to three tubes. Each tube contains environmental co
ID: 142896 • Letter: T
Question
The same DNA strand is added to three tubes. Each tube contains environmental conditions that are
similar to the other tubes with the exceptions listed below.
Tube 1 and 2 are incubated at 35°C while tube 3 is incubated at 90°C.
Tube 2 is at pH 6 while tubes 1 and 3 are at pH 13.
Tube 3 contains 10mM KCl while tubes 1 and 2 contains 1mM KCl.
Question: You then add the DNA solutions to cuvettes and stick them in a spectrophotometer set to 260nm. For which
tube do you expect to see the highest absorbance value?
The answer is tube 3. I just want a full explanation of why the tube with the most extreme conditions shows the most absorbance at 260nm. What is behind this causal relationship? Please explain in full details.
Explanation / Answer
The KCl acts by neutralising the charge present on the backbone of the DNA. All the adverse environmental conditions like high pH and high temperature which create positive charge on the DNA will be neutralised by KCl. The tube 3 contains higher concentration of KCl than the other tubes. Therefore, the highest absorbance was observed in the tube 3.
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