You have two fish named Fish and Fishy. Fish lives in a saltwater tank, and Fish
ID: 195007 • Letter: Y
Question
You have two fish named Fish and Fishy. Fish lives in a saltwater tank, and Fishy lives in a not saltwater tank. You are studying their DNA and have accidentally mixed up the DNA tubes and now you don't know which DNA is from Fish and which DNA is from Fishy (you can assume the DNA strands are all the same length). Luckily, you know there is a way to test which tube is from which fish. You monitor the absorbance of the DNA as a function of salt concentration, and obtain the graph below. Look at the graph below and analyze it to determine what it's telling you (it's a little bit different from the graphs we looked at in class) Tube B Tube A [Nacl] a. Which tube is from Fish and which tube is from Fishy? Use the graph above to justify your reasoning b. What interactions does the salt concentration affect in the DNA?Explanation / Answer
According to the question, Fish live in marine water body and Fishy lives in fresh water or low-salt water conditions.
(a) Tube-A has DNA of Fishy and Tube-B has DNA of Fish.
Explaination: Since Fishy lives in a tank with low salt concentration, it will readily cause the DNA to denature. After denaturation, double stranded molecule will be separated into 2 linear molecules (single strands) and when the absorbance is measured, the absorbance value will be higher for the single strands as compared to the double strands (also known as Hyperchromic Effect). If graph is analysed, it is concluded that-maximum value of absorbance is reached at lower salt concentrations than at higher salt levels. At higher salt concentrations, cations present in the salt will shield the negative charge on DNA molecule, thus, it will cause the molecule to stabilize and prevent it from getting denatured.
(b) Salt concentration disrupts the helix of the DNA molecule by breaking the hydrogen bonds between the base pairs.
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