You have four tubes containing the same sample of DNA at the

You have four tubes containing the same sample of DNA at the same concentration and at pH 7.5, but under different environmental conditions (listed below). The TM for this DNA molecule is 78°C at physiological salt conditions (~100 mM NaCl):

1.) DNA in an aqueous solution that has been digested completely to nucleotides with DNAse I enzyme.

2.) DNA in aqueous solution containing no salt and has been heated to 78°C.

3.) DNA in an aqueous solution containing physiological concentrations of salt and heated to 78°C.

4.) DNA in an aqueous solution containing physiological concentrations of salt and is heated only to 37°.

Match the samples above with their corresponding OD260 readings

OD60 = 0.271

OD260 = 0.475

OD260 = 0.620

OD260 = 0.960

a. DNA in an aqueous solution that has been digested completely to nucleotides with DNAse I enzyme.

b. DNA in aqueous solution containing no salt and has been heated to 78°C.

c. DNA in an aqueous solution containing physiological concentrations of salt and heated to 78°C.

d. DNA in an aqueous solution containing physiological concentrations of salt and is heated only to 37oC.

Solution

Answer:

As DNA gets dentured due to temperature, OD₂₆₀ goes on increasing. Addition of salt causes the Tm to increase.

(a) DNA in an aqueous solution that has been digested completely to nucleotides with DNAse I enzyme = 0.960

(b) DNA in aqueous solution containing no salt and has been heated to 78°C = 0.620

(c) DNA in an aqueous solution containing physiological concentrations of salt and heated to 78°C = 0.475

(d) DNA in an aqueous solution containing physiological concentrations of salt and is heated only to 37° = 0.271